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Diseases of the Nose, Sinuses, and Skull Base David W. Kennedy, MD Rhinology Professor Department of OtorhinolaryngologyHead and Neck Surgery Perelman School of Medicine University of Pennsylvania Philadelphia, Pennsylvania
Peter H. Hwang, MD Professor and Chief Division of Rhinology and Endoscopic Skull Base Surgery Department of OtolaryngologyHead and Neck SurgeryStanford University School of Medicine Stanford, California
Foreword by Heinz R. Stammberger, MD, Hon. FRCS (Ed.), Hon. FRCS (Eng), Hon. FACS Professor and Head Department of General ENTHead and Neck Surgery Medical University Graz Graz, Austria
Christine Gralapp, MA, CMI Medical Illustrator ThiemeNew York Stuttgart Copyright 2012 by Thieme Medical Publishers, Inc.
Foreword Preface Acknowledgments Contributors
I. Sinonasal Anatomy and Physiology
Chapter 1 Sinonasal Development and AnatomySarah K. Wise, Richard R. Orlandi, and John M. DelGaudio Chapter 2 Sinonasal PhysiologyDavid A. Gudis, Bradford A. Woodworth, and Noam A. Cohen Chapter 3 Radiologic Imaging of the Paranasal Sinuses and Skull BaseLaurie A. Loevner and Igor Mikityansky Chapter 4 Olfaction and TasteErin K. OBrien, Jose G. Gurrola II, and Donald A. Leopold Chapter 5 Objective Measures of Nasal FunctionJohn F. Pallanch
II. Medical Aspects of Sinonasal Disease
Chapter 6 Allergic and Nonallergic Rhinitis Marie-Nolle Corriveau and Claus Bachert Chapter 7 Principles of Allergy Skin Testing and Immunotherapy Daniel L. Hamilos Chapter 8 Unified Airway DiseaseElina Toskala Chapter 9 The Diagnosis of RhinosinusitisVictoria A. Epstein and Donald C. Lanza Chapter 10 Sinonasal Manifestations of Systemic DiseaseShaun J. Kilty, Reza Alizadehfar, and Martin Desrosiers Chapter 11 Infectious RhinitisJayant M. Pinto, Fuad M. Baroody, and Robert M. Naclerio Chapter 12 Acute RhinosinusitisJoseph K. Han and Stephen M. Wold Chapter 13 Etiologic Factors in Chronic RhinosinusitisAndrew P. Lane and Justin H. Turner Chapter 14 Nasal PolyposisRakesh K. Chandra, David B. Conley, and Robert C. Kern Chapter 15 Microbiology of Rhinosinusitis and Antimicrobial ResistanceKevin C. Welch, James N. Palmer, and Alexander G. Chiu Chapter 16 Fungal RhinosinusitisMatthew W. Ryan and Bradley F. Marple Chapter 17 Medical Therapies for Rhinosinusitis: Anti-InfectiveHoward S. Moskowitz and Berrylin J. Ferguson Chapter 18 Medical Therapies for Rhinosinusitis: Anti-InflammatoryRajiv K. Bhalla and Erin D. Wright Chapter 19 Management of Recalcitrant Chronic Rhinosinusitis Following Endoscopic Sinus SurgeryNathan B. Sautter and Timothy L. Smith Chapter 20 Pediatric RhinosinusitisJanaki Emani, Dana L. Suskind, and Fuad M. Baroody
Chapter 21 Complications of RhinosinusitisIan J. Witterick and Allan D. Vescan
III. Surgical Aspects of Sinonasal Disease
Chapter 22 Office Rhinology and Surgical BiomaterialsRichard R. Orlandi and Peter H. Hwang Chapter 23 Surgical Navigation and Intraoperative ImagingMartin J. Citardi Chapter 24 Instrumentation in Sinus SurgeryTroy D. Woodard and James A. Stankiewicz Chapter 25 Functional Endoscopic Sinus Surgery: Concepts, Surgical Indications, and TechniquesDavid W. Kennedy and Vijay R. Ramakrishnan Chapter 26 Revision Functional Endoscopic Sinus Surgery Francis T.K. Ling and Stilianos E. Kountakis Chapter 27 Endoscopic Frontal SinusotomyYvonne Chan, Christopher T. Melroy, and Frederick A. Kuhn Chapter 28 Advanced Frontal Surgery TechniquesKaren Anne Bednarski and Brent A. Senior Chapter 29 Complications of Endoscopic Sinus Surgery: Prevention and ManagementRalph B. Metson and Michael P. Platt Chapter 30 Congenital Sinonasal DisordersMan-Kit Leung, Paul R. Krakovitz, and Peter J. Koltai Chapter 31 Benign Sinonasal TumorsKristin Seiberling and Peter-John Wormald Chapter 32 Malignant Sinonasal TumorsValerie J. Lund Chapter 33 Endoscopic Applications in Orbital SurgeryTodd T. Kingdom and Vikram D. Durairaj Chapter 34 Surgery of the Septum and TurbinatesParul Goyal and Peter H. Hwang Chapter 35 Functional RhinoplastySam P. Most Chapter 36 Sinonasal TraumaE. Bradley Strong and Travis T. Tollefson Chapter 37 EpistaxisWinston Vaughan, Manish Khanna, and Karen Fong Chapter 38 Rhinologic Aspects of Sleep-Disordered BreathingShannon S. Sullivan, Oscar Carrillo, and Robson Capasso Chapter 39 External Approaches to the Paranasal SinusesAndrew H. Murr and Andrew N. Goldberg Chapter 40 Evidence-Based Medicine in Rhinology and Skull Base SurgeryMichael G. Stewart
IV. Surgical Aspects of Skull Base Disease
Chapter 41 Endoscopic Anatomy of the Skull Base and Parasellar RegionLuigi Maria Cavallo, Paolo Cappabianca, Felice Esposito, Isabella Esposito, Domenico Solari, and Manfred Tschabitscher Chapter 42 Pathology of the Sinonasal Region and Anterior and Central Skull BaseMichael J. Kaplan, Griffith R. Harsh IV, Benzion Joshua, Deborah J. Chute, and Gerald J. Berry Chapter 43 The NasopharynxDharmbir S. Sethi and Hin Ngan Tay Chapter 44 Cerebrospinal Fluid Leaks and EncephalocelesBradford A. Woodworth and Rodney J. Schlosser
Chapter 45 Endoscopic Approaches to the Anterior Cranial FossaJean Anderson Eloy, Belachew Tessema, and Roy R. Casiano Chapter 46 Endoscopic Approaches to the Sella and Suprasellar Region Anne E. Getz, Edward R. Laws, and Peter H. Hwang Chapter 47 Endoscopic Approaches to the Petrous Apex and Cavernous SinusPaolo Castelnuovo, Andrea Pistochini, and Piero Nicolai Chapter 48 Endoscopic Approaches to the Clivus and Posterior FossaAldo C. Stamm, Leonardo Balsalobre, and Larry Hilton Kalish Chapter 49 Endoscopic Approaches to the Pterygopalatine and Infratemporal FossaeAmeet Singh, Vijay K. Anand, and Theodore H. Schwartz Chapter 50 Transnasal Endoscopic Approach to the Craniocervical JunctionJayakar V. Nayak and Stefan A. Mindea Chapter 51 Extended Applications of Endoscopic Skull Base SurgeryCarl H. Snyderman, Paul A. Gardner, and Daniel M. Prevedello Chapter 52 Endoscopic Skull Base ReconstructionAdam M. Zanation, Mihir R. Patel, Ricardo L. Carrau, and Daniel M. Prevedello Chapter 53 Complications of Endoscopic Skull Base SurgeryErnesto Pasquini and Giorgio Frank Chapter 54 Cranial and Combined ApproachesMichael J. Kaplan, Nancy J. Fischbein, and Griffith R. HarshIV Index
It is rare in the history of medicine that a new diagnostic and surgical concept has had such a decisive and ongoing impact on a specialty as the advent of the endoscope and endoscopic sinus surgery has had on rhinology. The ability to look into the most remote corners and niches of the nose and sinuses has led to improved understanding of pathophysiology, which in turn triggered the curiosity of many clinicians and scientists to further explore the infective, inflammatory, allergic, and immunologic backgrounds of many of the diseases encountered. Transnasal endoscopic surgery developed from its humble beginnings in the early 1970s to a degree of sophistication unimaginable 20 or even 10 years ago. In interdisciplinary cooperation, rhinologists and neurosurgeons have started to go for and through the skull base, toward the pituitary, clivus, petrous apex, and well beyond toward intracranial lesions. Rhinology, over the last few decades, has developed from a field of interest only for idiosyncratic researchers into one of the most exciting and attractive rapidly developing and expanding topics of modern medicine.This fascinating development and its achievements are documented in a masterly fashion in this book and MCC, for which David W. Kennedy and Peter H. Hwang have to be congratulated. Its plain title Rhinology: Diseases of the Nose, Sinuses, and Skull Base does not at first glance reveal the true treasures hidden inside: David and Peter have managed to bring together many of the best experts in their respective fields to contribute chapters the contributors names read like the whos who of the opinion leaders globally. This book reflects the devel opments of the last 30 years, and the interdisciplinary nature of rhinology brings together anatomists, physiologists, allergologists, immunologists, radiologists, endocrinologists, basic researchers, rhino-and neurosurgeons, and more. Whereas normally books and their chapters lag behind the latest advances and journal publications, with this book it is different. Here, the contemporary experience of the worlds top experts is one of the books core values; one can clearly feel the editors work throughout the chapters, highlighting work and research in progress whenever appropriatethere is no dogmatic approach anywhere in this book! That Thieme Medical Publishers has taken extra effort by providing the great medical illustrator Christine Gralapp, who has created unique and clear color drawings throughout the volume, adds to the overall outstanding quality of this book. The accompanying MCC is of high quality, illustrative, and very educational. The fact that though the videos are by various experts David Kennedy personally narrates all of them provides a welcome consistency for the viewer.There has never been a book on rhinology that is as complete and up-to-date as this oneit will be a benchmark for the decades to come! Heinz R. Stammberger, MD, Hon. FRCS (Ed.),Hon. FRCS (Eng), Hon. FACS Professor and Head, Department of General ENTHead and Neck Surgery Medical University Graz Graz, Austria
1 Sinonasal Development and Anatomy
Sarah K. Wise, Richard R. Orlandi, and John M. DelGaudio
Sinonasal Development
Understanding the anatomy of the paranasal sinuses and surrounding structures is integral to performing safe and appropriate sinus surgery through endoscopic and open techniques. In addition, knowledge of the embryologic development of the paranasal sinuses allows for better comprehension of the spatial involvement of disease processes affecting the sinuses. Because the nasal and paranasal sinus structures develop from multiple bones, rather than a single bone, understanding the developmental relationship between these bones allows the surgeon to better evaluate and treat certain disease processes that affect the sinonasal cavities. The primary bones from which the paranasal sinuses develop are the maxillary, ethmoid, sphenoid, and frontal bones. There are also lesser contributions to paranasal sinus development from the lacrimal and zygomatic bones. Development of the four sets of paired paranasal sinuses is discussed in detail here. The nasal septum develops from four sources: the perpendicular plate of the ethmoid bone, the maxillary bone (crest), the vomer, and the quadrangular cartilage.
Nasal Cavity Development
Early development of the sinonasal cavity begins during the 8th week of fetal life. At this time, the nasal septum can be seen dividing the right and left sides of the future nasal cavity. At 8 weeks gestation, the nasal septum is a mesenchymal structure that is partially differentiated into cartilage.1 Also beginning at 8 weeks, several ridges begin to develop along the lateral nasal wall.2 These lateral nasal wall ridges are the earliest signs of the developing turbinates. Surrounding the embryologic nasal cavity a cartilaginous capsule forms, and at 9 to 10 weeks the cartilaginous capsule contributes finger-like projections to the developing turbinates.2 Also between 9 and 12 weeks gestation, a separate cartilaginous and soft tissue bud forms between the developing middle and inferior turbinates.1,2 This bud will become the uncinate process (Fig. 1.1). The ridges along the lateral nasal wall, which will ultimately develop into the turbinates, have been reported to be of different origin by various authors throughout history. In 1895, Killian described the inferior turbinate as originating from the maxillary process and termed this developing structure the maxilloturbinal.3 Killian further described the more superiorly located ethmoturbinals as forming the middle and superior turbinates, with a small nasoturbinal forming the agger nasi region. Stammberger supports the maxilloturbinal origin of the inferior turbinate, but notes some subtle differences in the ultimate development of the five described ethmoturbinals, with approximately four of the ethmoturbinals remaining throughout development and eventually forming the agger nasi region (superior portion of first ethmoturbinal or nasoturbinal), middle turbinate (second ethmoturbinal), superior turbinate (third ethmoturbinal), and supreme turbinate (fourth and fifth ethmoturbinals).4 In contrast to Killian and Stammberger, Bingham et al. have described the inferior turbinate as arising from the cartilaginous nasal capsule along with the middle and superior turbinates and they do not support separate maxilloturbinal terminology.2
At 15 to 16 weeks gestation, the inferior, middle, and superior turbinates are clearly formed and easily visible in embryologic sections.2 As seen from developmental histologic sections, the middle and superior turbinates arise from precursors of the ethmoid bone, whereas the inferior turbinate bone is independent, receiving contributions of its final adult structure from the cartilaginous nasal capsule and the bone of the maxilla.2 Between the ethmoturbinal ridges are primary furrows, which will form the recesses and meatuses that separate the adult turbinates.46 The first and second ethmoturbinals are separated by the first primary furrow, which becomes the middle meatus, ethmoid infundibulum, hiatus semilunaris, and part of the frontal recess in the adult. The superior and supreme meatuses are derived from the second and third primary furrows, respectively. The extent of adult paranasal sinus pneumatization and development differs greatly from person to person. This is thought to result from the extent of invagination and evagination between the developing turbinates and their intervening furrows.5
Sinonasal Mucosa and Olfactory Development
In a histologic study of human fetal heads, Wake et al.1 have elegantly described the development of the sinonasal mucosa. In summary, as the nasal cavity begins to develop at 8 we eks gestation, a hypercellular mesenchymal capsule forms around the developing nasal structures. Although the majority of the nasal cavity contains undifferentiated cells or stratified cuboidal cells, the nasal septum is partially differentiated into cartilage at this time, and olfactory epithelium can be seen in the superior aspect of the nasal cavity. By 9 to 10 weeks, the cartilaginous nasal capsule has fully differentiated, ciliated pseudostratified columnar or cuboidal epithelium is seen on the septum and inferior turbinate, and primitive blood vessels are present. At 11 to 12 weeks, the septal epithelium has differentiated into characteristic ciliated respiratory epithelium and secretory goblet cells are present, but the lateral nasal wall mucosa continues to be less differentiated. The cribriform plate is present in cartilaginous form at 14 to 16 weeks, with neurovascular bundles penetrating it, and olfactory epithelium is present throughout the superior portion of the nasal cavity. Also at 14 to 16 weeks, stratified squamous epithelium with hair follicles can be seen in the nasal vestibule. The mucosal lining of the developing paranasal sinuses remains spherical or cuboidal with few cilia and glands. By 17 to 18 weeks, the lateral nasal wall and ethmoid sinus mucosa has matured to respiratory epithelium, with higher concentrations of goblet cells anteriorly and ciliated cells posteriorly. At 20 to 24 weeks, secretory cells are more evenly
distributed and vascular structures are present throughout the lamina propria, resembling postnasal development. Postnatally, there is partial regression of the olfactory epithelium such that it occupies only the area of the cribriform plate and superior turbinate.
Ethmoid Sinuses
The ethmoid sinus is the first to develop into detectable pneumatized cells in the fetus. Early anterior ethmoid cells, including the cartilaginous beginnings of the ethmoid bulla, form as a result of budding from the middle meatus around 11 to 12 weeks of fetal life.1,7 At 14 to 16 weeks some anterior ethmoid cells are well formed.1 Wake et al.1 report that, by 17 to 18 weeks, the posterior ethmoid buds begin to develop from the superior meatus. Ossification of the ethmoid sinuses and lamina papyracea has occurred by 20 to 24 weeks gestation.1,7At birth the ethmoid sinuses are the most mature of the paranasal sinuses, being completely developed in the number of cells but not in size.8 In the newborn, the ethmoid complex is 8 to 12 mm long, 1 to 3 mm wide, and 1 to 5 mm in height. The ethmoid sinuses undergo significant growth during the first decade of life. Wolf et al.8 note the most rapid expansion of the ethmoid complex between 1 and 4 years of age, whereas Shah et al.9 have demonstrated the most rapid anteroposterior expansion of the ethmoid sinuses occurs between 3 and 8 years of age. By age 12, the ethmoid sinuses have essentially reached their adult dimensions.8,9 The ethmoid cells can, however, expand beyond the boundaries of the ethmoid bone to extend into the frontal recess (frontal cells, suprabullar cells, and frontal bullar cells), sphenoid bone (sphenoethmoid [Onodi] cell), and maxillary bone (infraorbital ethmoid [Haller] cell). The ethmoid bone contains more than the ethmoid sinuses. Other structures that are derived from the ethmoid bone include the middle turbinate, superior turbinate, supreme turbinate, cribriform plate, and the posterosuperior portion of the nasal septum (perpendicular plate of the ethmoid).
Maxillary Sinus
The maxilla begins to ossify at 11 to 12 weeks gesta tion, as the early anterior ethmoid sinuses are developing.1 The maxillary infundibulum becomes evident at week 14 to 16 of fetal life as an invagination of the maxillary bone, found lateral to the uncinate ridge. At this point there is still no true maxillary sinus cavity. By 17 to 18 weeks gestation, an air space is clearly seen lateral to the developing uncinate process, protruding toward the woven bone of the maxilla.2 The developing maxillary sinus can be differentiated from the nasolacrimal duct at this stage as well.2 Thereafter, as the cartilaginous capsule resorbs or ossifies, dependent on location, the maxillary sinus grows larger.2,5,7,10 Over the second and third trimesters the maxillary sinus continues to enlarge from the maxillary infundibulum. At birth the maxillary sinus measures ~10 mm long, 4 mm wide, and 3 mm in height.8 By age 4 the maxillary sinus has expanded laterally to the level of the infraorbital nerve and inferiorly to the level of the inferior turbinate attachment. At 8 years old, growth of the maxillary sinus typically extends laterally past the infraorbital canal and inferiorly to the middle of the inferior meatus. By age 12 the maxillary sinus extends laterally into the zygomatic recess, medially to the nasolacrimal duct, and inferiorly to the level of the floor of the nasal cavity (Fig. 1.2). Shah et al.9 have noted that the transverse diameter of the maxillary sinus expands most rapidly between 1 and 8 years of age, and the maxillary sinus vertical height increases rapidly between 1 and 5 years of age. The infants midface is very small, which results in significant differences in the maxillary sinus between the infant and the adult. In the infant and young child, the roof of the maxillary sinus slopes inferolaterally, as the orbit occupies a large portion of the midface. At this stage, the floor of the maxillary sinus lies at a level above the level of the nasal floor due to the presence of unerupted teeth. With midfacial growth and eruption of permanent teeth in childhood, the sinus continues to aerate, resulting in a more horizontal orientation of the orbital floor and inferior growth of the maxillary sinus floor to a level at or below the nasal floor. The development and ultimate size of the maxillary sinus can be influenced by many factors. Rarely, the maxillary sinus fails to develop, with cancellous bone ultimately filling the maxilla. Early childhood trauma can result in hypoplasia, possibly due to inadequate aeration of the sinus to permit expansion. Failure of eruption of the permanent dentition can result in shortening of the inferior vertical growth of the sinus. Hypoplasia of
the maxillary sinus can also occur in the absence of any other factors such as unerupted teeth or trauma. Patients with cystic fibrosis frequently have hypoplastic maxillary sinuses, possibly related to physiologic obstruction of the ostium, reduced aeration, and impaired pneumatization of the maxilla.11
Sphenoid Sinus
Development of the sphenoid sinus begins in the third to fourth month of fetal life as an invagination of the nasal cavity mucosa into the cartilaginous nasal capsule, termed the cartilaginous cupolar recess of the nasal cavity.12 At this time the nasal cavity invagination that will become the sphenoid sinus is not actually in contact with the sphenoid bone, but rather comes from the area of the posterior ethmoid via the ossiculum Bertini or Bertini bone.5,8 At this stage, the sphenoid bone has two ossification centers, separated by the canalis pharyngeus.8 Over the first few years of life, the cartilage that separates the ossiculum Bertini from the sphenoid bone will be resorbed and pneumatization of the sphenoid sinus will progress into the sphenoid bone itself. Although Shah et al.9 were able to identify minimally developed sphenoid sinuses in 33% of newborns radiographically, in most instances only the sphenoid ostium can be identified at birth. Pneumatization of the sphenoid sinus begins at age 1, with the most rapid growth reported between age 3 months and 5 years.9 Various authors have noted that by approximately age 12, adult size of the sphenoid sinus is reached.8,12 Wolf et al.8 have commented that beyond age 12 the sinus may continue to change shape, although the size remains fairly constant. Interestingly, in a study of sphenoid sinus aeration over the lifespan, Yonetsu et al.13 report that pneumatization of the sphenoid sinus does not reach its maximum until the end of the third decade of life. Following the third decade, these authors note that sphenoid aeration may actually decrease, with possible causes being loss of small vessels, hypoxia, and mucosal atrophy leading to bone deposition.13 Surrounding the sphenoid sinus are multiple important neurovascular structures, including the pituitary gland and optic chiasm in the superior medial position, internal carotid arteries and cavernous sinuses in the superior lateral position, and vidian nerves inferolaterally. The degree of sphenoid pneumatization with respect to the sella is often described by visualization in the sagittal plane. Vidic reported that sellar (including postsellar)
pneumatization was most common (83.6%), defined as sphenoid pneumatization extending posterior to a vertical line drawn through the tuberculum sella.12 Further delineating sphenoid pneumatization in the sagittal plane, Batra et al. note that postsellar pneumatization (extending beyond the posterior wall of the sella) is actually found in 65% of cases.14 Pneumatization of the sphenoid sinus may also occur in surrounding bony processes, such as the pterygoid process, greater and lesser sphenoid wings, anterior clinoid processes, and palatine bone, among others. The greater the aeration, the greater the likelihood that the neurovascular structures that are adjacent to the sphenoid sinus will appear in bony relief on the lateral wall or roof of the lateral extensions (Fig. 1.3). In addition, arachnoid granulations often occur in the proximity of the second branch of the trigeminal nerve in the pterygoid recess of well aerated sphenoid sinuses.15 These areas may ultimately result in spontaneous cerebrospinal fluid leaks or meningoencephaloceles in patients with benign intracranial hypertension. The degree of postnatal development of the sphenoid sinus may be affected by chronic disease or possibly genetic factors. For example, patients with cystic fibrosis (CF) tend to have hypoplastic sphenoid sinuses (Fig. 1.4A). Furthermore, CF patients homozygous for the delta-F508 mutation have a greater incidence of sphenoid hypoplasia than those with other CF genotypes.11 Whether this is related to the effect of genetic factors on sinus development or postnatal mucosal pathophysiology is unclear.
Frontal Sinus
The frontal sinuses are the last paranasal sinuses to begin developing and the last to complete development. There are various potential interpretations of the exact development of the frontal sinus, with some common themes. In 1916, Schaeffer described several (one to four) frontal furrows or pits being present during embryologic development that ultimately form the frontal sinus and various anterior ethmoid cells.6 Kasper further delineated these frontal furrows as forming the agger nasi cell (first furrow), frontal sinus (second furrow), and anterior ethmoid cells as they aerate into the ethmoid bone or the orbital portion of the frontal bone (third and fourth furrows) in the majority of specimens dissected.16 Kasper also notes that the frontal sinus may originate from frontal anterior ethmoid cells and frontal furrows (57%), infundibular anterior ethmoid cells (34%), extension of the ethmoid infundibulum (4%), direct extension of the frontal recess (3%), or least commonly by expansion of a suprabullar cell (2%).16 Both Schaeffer and Kasper discuss multiple variations of frontal sinus and frontal recess pneumatization, confirming that early anatomists appreciated the distinct variability of this region.6,16 Finally, Stammberger supports the development of the frontal recess at the superior aspect of the groove between the first and second ethmoturbinals.4 As endorsed by Bolger, it is easy to imagine that, given the highly complex anatomy of the frontal recess and frontal sinus, these invaginations or furrows may ultimately pneumatize to varying degrees.5 Contributing to the intricacy of this area, the actual origin of the frontal sinus proper may form from any of the furrows, and multiple furrows may ultimately aerate the frontal bone as well.5,16
At birth the frontal sinus is not visible in most individuals, with only 12% of newborn computed tomography (CT) scans demonstrating minimally developed frontal sinuses.9 The frontal sinus is present by the age of 4, at 4 to 8 mm in length, 6 to 9 mm in height, and 11 to 19 mm in width.8 By age 12, the frontal sinus has achieved tetrahedral shape and continues to aerate until early adulthood (Fig. 1.2).8 As in the sphenoid sinus, the frontal sinus develops mostly in the postnatal period. Because of this, the frontal sinus is also subject to the same developmental issues, such as hypoplasia in cystic fibrosis patients (Fig. 1.4B).
Clinical Implications of Paranasal Sinus Development
An example of the importance of understanding sinonasal developmental anatomy as it relates to disease processes can be seen with monostotic fibrous dysplasia. The abnormal bone formation and expansion seen in monostotic fibrous dysplasia does not cross bony suture lines. Therefore, analysis of bony areas involved in this type of fibrous dysplasia can provide information about the embryologic derivation of various parts of the sinonasal cavities, such as the ethmoid and sphenoid bones (Fig. 1.5). In addition, mucoceles that obstruct the frontal recess can originate from multiple sources. Mucoceles involving the frontal recess may derive from agger nasi cells, frontal cells, suprabullar cells, and frontal bullar cells, or from the frontal sinus itself. Understanding the developmental origins of these various frontal recess cells may aid the otorhinolaryngologist and radiologist in evaluating imaging studies to determine the boundaries of the expanded bony walls and planning the location and extent of surgery necessary to adequately treat the pathology. As a final example, diseases such as CF often result in incomplete development of the sinuses. The maxillary and ethmoid sinuses are present at birth, whereas the sphenoid and frontal sinuses develop after birth. In many patients with CF, the sphenoid and frontal sinuses are rudimentary or absent.11 This paranasal sinus underdevelopment in CF patients may result from the underlying pathophysiological process in CF, in which thick secretions obstruct the sinuses and inhibit aeration, resulting in possible stunting of the development of the sphenoid and frontal sinuses (Fig. 1.4A,B).
Sinonasal Anatomy
This section focuses on sinonasal anatomy, beginning with schematic construction of the ethmoid complex. For many paranasal sinus surgeons, initial understanding of the ethmoid sinuses proves challenging. Simplified methodological construction of the ethmoid sinuses and surrounding structures will provide the framework for understanding the anatomy of the maxillary, frontal, and sphenoid sinuses as well.
Ethmoid Sinus
The ethmoid complex is just thatcomplex. Yet a thorough understanding of its anatomy and inherent variations is the key to safe and thorough surgery. Although the anatomy of the ethmoid sinuses can be as individual as a fingerprint, common landmarks and relationships guide its effective dissection. Stepwise construction of complex structures often aids in understanding them. For that reason, the construction of a simplified ethmoid sinus complex follows, along with anatomic descriptions and highlights.
Ethmoid Bulla
Schematic construction of the anterior ethmoid sinuses starts with a sphere. This sphere is then sectioned by a plane, and the smaller portion of the sphere is discarded. The thin sectioning plane or layer represents the
lamina papyracea. The partial sphere attached to the lamina papyracea represents the ethmoid bulla (Fig. 1.6A). As implied from our basic construction of the ethmoid complex, the ethmoid bulla is typically a rather large anterior ethmoid air cell that takes origin from the lamina papyracea along the medial wall of the orbit. Although ethmoid anatomy is often quite complicated, the ethmoid bulla is the most consistent and recognizable of the ethmoid cells. As the remainder of the ethmoid anatomy is added to the diagram, the relationship of the ethmoid bulla to surrounding structures will become evident: medial to the lamina papyracea, posterior to the uncinate process, anterior to the vertical basal lamella of the middle turbinate, and posteroinferior to the frontal recess. Stammberger describes minimal ethmoid bulla pneumatization or absence of ethmoid bulla occurring in ~8% of patients, referred to as a torus lateralis.4
Uncinate Process, Ethmoid Infundibulum, and Hiatus Semilunaris
A crescent-shaped line is added anterior to the ethmoid bulla and parallel to it. From this line, an outgrowth is then extended posteriorly and slightly away from the lamina papyracea and lateral nasal wall. This hookshaped outgrowth thus forms a trough with a vertical plane that parallels the anterior surface of the sphere (or ethmoid bulla). The term for this hook-shaped outgrowth is the uncinate process. As seen in Fig. 1.6B, the uncinate process conforms to the anterior and inferior aspects of the ethmoid bulla, and has a free edge without bony attachments posteriorly. At its anterior superior aspect, the uncinate process attaches to the ethmoidal crest of the maxilla and the posterior portion of the lacrimal bone, near the agger nasi region.5 At its posterior inferior aspect, the uncinate process fuses to the ethmoidal process of the inferior turbinate bone. The superior and posterior attachment of the uncinate process deserves special attention, as this attachment can have implications for the configuration of the frontal recess and frontal sinus outflow tract. Publications in the early 20th century, based on frontal recess anatomic dissections by Schaeffer6 and Kasper,16 indicate that the developmental origins of the frontal sinus and surrounding frontal recess structures are varied. Due to such variations, the frontal sinus outflow tract may drain directly into the superior aspect of the ethmoid infundibulum (less common), or into the middle meatus without a direct connection to the superior aspect of the ethmoid infundibulum (more common).6,16 The uncinate process most commonly inserts laterally onto the lamina papyracea, resulting in frontal sinus drainage that occurs medial to the uncinate process insertion and directly into the middle meatus between the superior aspect of the uncinate process and the middle turbinate attachment to the skull base.5,17 Less frequently, the uncinate process may insert onto the superior aspect of the middle turbinate or directly onto the skull base. In both of these cases, the frontal sinus drainage pathway will be lateral to the uncinate process and into the ethmoid infundibulum, which is described later. Finally, the posterior superior aspect of the uncinate process may have multiple attachments to the lamina papyracea, skull base, and middle turbinate.17 It is important to recognize that, due to the extreme variability of pneumatization of the frontal recess, these descriptions of the frontal sinus outflow tract are quite simplified and serve only as a framework for a basic understanding of this region.
The trough that is formed lateral to the uncinate process, within the anterior ethmoid complex, is called the ethmoid infundibulum. The ethmoid infundibulum is bounded medially by the lateral aspect of the uncinate process, laterally by the lamina papyracea, and posterosuperiorly by the ethmoid bulla.5,17 In addition, the frontal process of the maxilla and the lacrimal bone may also contribute to the anterior and superior boundaries of the ethmoid infundibulum.5,17 The importance of the superior attachment of the uncinate process and its relationship to the frontal sinus outflow tract have already been described. Of note, in the most common scenario of uncinate attachment to the lamina papyracea, the superior aspect of the infundibulum that is formed by the uncinate process attaching laterally to the lamina papyracea is a blind-ended configuration called the recessus terminalis.17 Access to the three-dimensional ethmoid infundibulum is through a two-dimensional semilunar-shaped gap or opening between the free margin of the uncinate process and the ethmoid bulla, called the hiatus semilunaris. Although commonly referred to simply as the hiatus semilunaris, Grunwald further classified this entrance to the ethmoid infundibulum as the hiatus semilunaris inferior.18 The hiatus semilunaris superior is then defined as the two-dimensional entrance to the sinus lateralis (described later) that is formed by the space between the posterior aspect of the ethmoid bulla and the anterior aspect of the middle turbinate basal lamella.
Agger Nasi Region
Within the anterior portion of the lateral nasal wall, a mound of bone that is often pneumatized is present. The term for this nasal mound is the agger nasi. When this area is pneumatized, it is called an agger nasi cell (Fig. 1.7A). The agger nasi region or cell is found anterior and inferior to the frontal sinus and frequently forms a portion of the anteromedial floor of the frontal sinus. The boundaries of the agger nasi cell are the frontal sinus superiorly and frontal recess superiorly and posteriorly, the frontal process of the maxilla anterolaterally, the nasal bones anteriorly, the lacrimal bones inferolaterally, and the uncinate process inferomedially.5 In the surgical treatment of frontal sinus disease, the agger nasi cell is important to recognize and remove, as it may contribute significantly to narrowing of the frontal recess and frontal sinus outflow tract. In cases of revision frontal sinus surgery, retained remnants of unopened agger nasi cells may also be identified narrowing outflow from the frontal sinus.19
Middle Turbinate
The addition of the middle turbinate completes the construction of the anterior ethmoid complex (Fig. 1.7A). The middle turbinate provides a medial and posterior boundary to the anterior ethmoid complex. The middle turbinate is a complex, three-dimensional structure, whose shape may not be intuitive initially. The portion of the middle turbinate that is initially visible on anterior rhinoscopy or nasal endoscopy is oriented in the parasagittal plane, with a free mucosal edge anteriorly and inferiorly. This portion of the middle turbinate may be pneumatized, forming a concha bullosa air cell. Bony attachment of the parasagittal portion of the middle turbinate occurs anterosuperiorly at the crista ethmoidalis of the maxilla, in the region of the agger nasi cell.4,17 The middle turbinate attachment to the skull base in the parasagittal plane occurs adjacent to the lateral lamella of the cribriform plate of the ethmoid bone. The portion of the middle turbinate that runs in the coronal plane and attaches to the skull base superiorly and the lamina papyracea laterally is called the vertical portion of the middle turbinate basal lamella (Fig. 1.7A D). The basal lamella of the middle turbinate separates the anterior and posterior ethmoid complexes. Although the concept of the vertical portion of the middle turbinate basal lamella may now be easy to grasp via simplified diagrams (Fig. 1.7A), in reality the middle turbinate basal lamella is rarely a smooth structure. The middle turbinate basal lamella is frequently indented from both anterior and posterior aspects by the ethmoid complexes on either side, adding to the intricacy of its shape.4,17 The vertical portion of the middle turbinate basal lamella may also be pneumatized, forming an interlamellar cell.4,5,18 Pneumatization of an interlamellar cell has been described as originating from the superior meatus.4Posteriorly, the middle turbinate basal lamella is oriented in a more axial plane, forming the horizontal portion of the middle turbinate basal lamella. The posterior bony attachment of the middle turbinate to the lateral nasal wall occurs at the crista ethmoidalis of the perpendicular process of the palatine bone, which is often used as an anatomic marker anterior to the sphenopalatine foramen.5,17
With the middle turbinate now visualized, the term ostiomeatal complex or ostiomeatal unit may be addressed. A functional rather than truly anatomic term, the ostiomeatal unit refers to the conglomerate of structures and sinuses that surround or drain into the middle meatus.20 Included are the anterior ethmoid, maxillary, and frontal sinuses; the uncinate process; and the ethmoid infundibulum. Due to the confluent anatomy of this region, and potentially narrow middle meatus drainage pathway, a relatively minor blockage in this important area may lead to obstruction of the frontal, anterior ethmoid, and maxillary sinuses.
Retrobullar and Suprabullar Recesses (Sinus Lateralis)
Situated between the bulla ethmoidalis and the middle turbinate basal lamella are the retrobullar and suprabullar recesses, which lie posterior and superior to the bulla ethmoidalis, respectively (Fig. 1.8). Sometimes referred to collectively as the sinus lateralis, these spaces are not actually sinuses but instead are potential spaces, or recesses, that are bounded by the ethmoid complex structures. The two-dimensional entrance to the sinus lateralis from the middle meatus is the hiatus semilunaris superior, situated between the posterior aspect of the ethmoid bulla and the anterior aspect of the middle turbinate basal lamella, as described previously. The sinus lateralis may be pneumatized to varying degrees, and at times, bony partitions may divide the suprabullar and retrobullar recesses. The sinus lateralis is bounded by the lamina papyracea laterally, the ethmoid bulla anteriorly, the middle turbinate basal lamella posteriorly, and the skull base superiorly.
Frontal Recess
Typically there is a superior projection from the bulla toward the roof of the ethmoid cavity which attaches to the skull base. This attachment is called the bulla lamella (Fig. 1.7A). The space anterior to the bulla lamella, which is bounded by the agger nasi cell anteriorly, the lamina papyracea laterally, and the middle turbinate medially, leads toward the frontal sinus ostium. This space is the frontal recess (Fig. 1.8). If a bulla lamella is not present connecting the ethmoid bulla to the skull base, the frontal recess may communicate with the suprabullar recess posterior to the ethmoid bulla.4,17 The frontal recess is described in more detail in the Frontal Sinus section of this chapter and in other chapters in this text specifically devoted to the anatomy and surgery of the frontal sinus.
Posterior Ethmoid Complex
The posterior ethmoid complex is now added (Fig. 1.9A C). The posterior ethmoid sinus has as its boundaries: the parasagittal portions of the superior and supreme turbinates medially, the anterior face of the sphenoid sinus posteriorly, the lamina papyracea laterally, the middle turbinate basal lamella anteriorly, and the skull base superiorly. There are approximately one to five air cells that occupy this posterior ethmoid space.5 It is important to recognize the critical structures that may be encountered around the posterior ethmoid sinuses. A highly pneumatized posterior ethmoid cell can aerate posteriorly over the superolateral aspect of the true sphenoid sinus21; this anatomic variant is commonly referred to as an Onodi cell. The term sphenoethmoid cell is now preferred over Onodi cell, as it is more illustrative of the anatomy in this area.17 When a sphenoethmoid cell is present, the posterior aspect of the lamina papyracea, optic nerve, and occasionally carotid artery may be seen as bony reliefs on the superolateral aspect of the posterior ethmoid wall, rather than in the sphenoid sinus. The prevalence of sphenoethmoid cells on imaging has been reported to be 28.1%.22 A sphenoethmoid cell may often be recognized on CT scan imaging by its position in the superolateral aspect of what initially appears to be a septated sphenoid sinus on a coronal CT scan (Fig. 1.10A,B). By tracing this cell in axial, coronal, and sagittal images, the surgeon will often realize the true origin of the cell is from the posterior ethmoid, rather than the sphenoid sinus. In such images, the true sphenoid sinus is most commonly located in the medial inferior position on coronal imaging.
Fig. 1.9 (A) Ethmoid complex schematic with the superior turbinate (ST), the posterior ethmoid area, and the sphenoid sinus ostium (SO) shown. The anterior ethmoid is bounded medially by the middle turbinate, whereas the posterior ethmoid is bounded medially by the superior turbinate. The vertical basal lamella of the middle turbinate separates the anterior and posterior ethmoid complexes. (B) Sagittal cadaver dissection demonstrating the position of superior, middle, and inferior turbinates and their respective meatuses with respect to the sphenoid sinus and skull base. (C) Oblique orientation of a sagittal cadaver dissection revealing a turbinate position with respect to the sphenoethmoid recess, the sphenoid sinus ostium (metal probe), and the nasopharynx. U, uncinate process; L, lamina papyracea; ST, superior turbinate; SM, superior meatus; MT, middle turbinate; MM, middle meatus; ST, superior turbinate; IT, inferior turbinate; IM, inferior meatus; SO, sphenoid sinus ostium; Sph, sphenoid sinus; Pit, pituitary gland; Cl, clivus; ET, eustachian tube orifice; SER, sphenoethmoid recess; NP, nasopharynx.
Paranasal Sinus Drainage Patterns
The anterior ethmoid complex is bounded medially by the middle turbinate. Likewise, the superior turbinate forms the medial boundary of the posterior ethmoid cells. Note that the middle and superior turbinates share a common skull base attachment and run in the same parasagittal plane. The vertical portion of the middle turbinate basal lamella is oriented in the coronal plane, dividing the anterior from the posterior ethmoid cells. Following the addition of the middle and superior turbinates, the middle and superior meatuses may be visualized as well. The superior, middle, and inferior meatuses lie in the space inferior and lateral to their respective turbinates (Fig. 1.9B). A supreme turbinate may be present in some patients as well, with its meatus inferior and lateral to the turbinate. Due to their developmental origin from the precursors of the middle meatus, the anterior ethmoid, frontal, and maxillary sinuses drain into the middle meatus. The posterior ethmoid sinuses drain into the superior meatus and the supreme meatus, if present. In examining a partial sagittal dissection of the ethmoid complex, one may appreciate multiple lamellae that lie in an oblique, roughly parallel plane (Fig. 1.11).5,23 From anterior to posterior, the first lamella visualized is the uncinate process, followed by the ethmoid bulla. The third and fourth lamellae are the basal lamellae of the middle turbinate and superior turbinate, respectively. These lamellae may also be seen during endoscopic surgical dissections as work progresses in an anterior to posterior direction. Addition of the nasal septum completes the construction (Fig. 1.12A,B). The sphenoid sinus drains into the sphenoethmoid recess, which lies medial to the superior and supreme turbinates, lateral to the posterior nasal septum, inferior to the skull base, and superior to the nasopharynx.
Ethmoid Roof and Skull Base
The roof of the ethmoid sinuses is formed by the orbital plate of the frontal bone laterally and the lateral lamella of the cribriform plate of the ethmoid bone medially.5 Whereas the lateral aspect of the ethmoid roof is thicker (0.5 mm), the medial aspect of the ethmoid roof at the cribriform plate lateral lamella is only 0.2 mm thick. The thinnest point in the ethmoid roof is found along a groove in the cribriform plate lateral lamella at the site of the anterior ethmoid artery (0.05 mm thick), representing the most common site for iatrogenic cerebrospinal fluid leak during sinus surgery.24 The thin medial aspect of the ethmoid roof must be observed during any endoscopic sinus surgery. However, Keros further delineated olfactory sulcus depth classifications that can highlight the potential for iatrogenic injury to the cribriform plate lateral lamella.25 Keros type 1 is defined as an olfactory sulcus depth of 1 to 3 mm, and Keros type 2 is an olfactory sulcus depth of 4 to 7 mm. Finally, Keros type 3 represents an olfactory sulcus depth of 8 to 16 mm, and leaves a significant amount of thin cribriform plate lateral lamella along the medial aspect of the ethmoid roof. With increasing Keros type, there is lesser contribution from the thick frontal bone forming the ethmoid roof, with more of the ethmoid roof being formed by the thin cribriform plate lateral lamella. Therefore, as Keros type increases, there is an increased risk of cerebrospinal fluid leak during sinus surgery.5 Recent radiologic analysis of cribriform plate lateral lamella dimensions performed by Solares et al.26 has revealed that Keros type 1 was the most common type identified (83%), which differs from Keros original report of type 2 being the most common (70%).25
When studying the anatomy of the ethmoid roof preoperatively, the surgeon must also recognize asymmetries between sides. Due to differences in development, ethmoid roof height may be considerably lower on one side of a patient in comparison to the other, and Keros classifications may also differ between sides. Finally, the vertical orientation of the cribriform plate lateral lamella should also be assessed, as this area may range from truly vertical to obliquely oriented. In more oblique orientations of the cribriform plate lateral lamella, the medial aspect of the ethmoid roof will be quite thin and great care should be exercised in this area. The anterior ethmoid artery is another important surgical landmark associated with the ethmoid skull base. The anterior ethmoid artery runs in an anteromedial direction from the orbit to enter the skull base at the ethmoidal sulcus in the lateral lamella of the cribriform plate.24 The anterior ethmoid artery often runs along the skull base, but in well pneumatized ethmoid sinuses, it may be found 1 to 3 mm below the ethmoid roof in a mesentery. On coronal CT scan imaging, the anterior ethmoid artery may be seen leaving the orbit as a
projection medially. This anterior ethmoid artery projection can be identified on coronal imaging at the approximate location where the medial rectus and superior oblique muscles are in closest proximity within the orbit, or near the most anterior visualization of the optic nerve just posterior to the globe.
Within the ethmoid infundibulum trough is the opening into the maxillary sinus or maxillary ostium (Fig. 1.13A C). In anatomic descriptions of the maxillary sinus ostium, Van Alyea described the natural ostium of the maxillary sinus as lying in the posterior one-third of the infundibulum in 71.8% of cases.10 On the anterior and posterior aspects of the uncinate process attachment to the inferior turbinate bone lie the anterior and posterior fontanelles.5 Representing bony dehiscences of the medial wall of the maxillary sinus, the anterior and posterior fontanelles are made up of only mucosa of the middle meatus, connective tissue, and mucosa of the maxillary sinus. According to Van Alyea, ~23% of patients have defects in the mucosal covering of the medial wall of the maxillary sinus in the posterior fontanelle, resulting in accessory ostia.10 In the adult with normal maxillary sinus pneumatization, the boundaries of the maxillary sinus cavity are the alveolar portion of the maxilla inferiorly, the zygoma laterally, the orbital floor superiorly, the pterygopalatine fossa and infratemporal fossa posteriorly, and the inferior turbinate, uncinate process, and anterior and posterior fontanelles medially.5 As with the other paranasal sinuses, the maxillary sinus may exhibit varying degrees of pneumatization, and in some cases, may be hypoplastic. According to Eggesbo et al., five criteria have been proposed for deeming a maxillary sinus hypoplastic in CF, a common setting of hypoplastic sinuses.27 These criteria for maxillary hypoplasia include four of the following five: an oval-shaped sinus, an enlarged oval-shaped orbit, a lack of pneumatization of the maxillary sinus below the level of the nasal floor, the medial maxillary sinus wall lateral to a vertical line drawn tangential to the medial orbit, and the lateral extent of the maxillary sinus medial to a vertical line through the middle of the orbit at the level of the infundibulum in the coronal plane. Due to the increased ratio of orbital volume to maxillary sinus volume in cases of maxillary sinus hypoplasia, the paranasal sinus surgeon must exercise caution when operating in and around a hypoplastic maxillary sinus. In these cases, the uncinate process is typically displaced inferolaterally and lies in close proximity to the orbital wall. In addition, owing to the common developmental origins of the uncinate process, the ethmoid infundibulum, and the maxillary sinus, underdevelopment of the uncinate process may be associated with more significant degrees of maxillary sinus hypoplasia.28
Originally described in 1765, the Haller cell is the most frequent anatomic variation seen in the maxillary sinus.17 Now termed an infraorbital ethmoid cell to precisely describe its anatomic location, this cell is thought to pneumatize from the anterior ethmoid (88%) or posterior ethmoid (12%) sinuses.17,29 By virtue of its location along the inferomedial orbit contiguous with the natural drainage pathway of the maxillary sinus, the infraorbital ethmoid or Haller cell may narrow the maxillary sinus ostium and ethmoid infundibulum and may contribute to obstruction in this area (Fig. 1.14).
The most anterosuperior portion of the ethmoid region that connects with the frontal sinus defines the frontal recess.17 Although the anatomy of the frontal recess may vary greatly, the general boundaries of the frontal recess include the posterosuperior aspect of the agger nasi cell, the superior lateral aspect of the middle turbinate within the middle meatus, the anterior wall of the ethmoid bulla and bulla lamella, and the lamina papyracea (Fig. 1.15AC).5,17 As stated previously, if a bulla lamella is not present, the frontal recess may communicate directly with the sinus lateralis and the suprabullar recess.17
Previously termed the nasofrontal duct, the frontal sinus outflow tract does not form a true duct. Rather, the frontal recess forms an hourglass shape that is best appreciated in the parasagittal orientation, with the narrowest portion being the internal frontal sinus ostium (Fig. 1.16).17 Superior to the internal frontal sinus ostium, the frontal sinus aerates into the frontal bone. On parasagittal view, the anterior and posterior tables of the frontal sinus can be visualized, and their differing thicknesses may be appreciated. The frontal sinus anterior table (412 mm) is considerably thicker than the posterior table (0.1 4.8 mm).30
There is significant variation in frontal recess and frontal sinus anatomy. The anatomy of this region is covered in detail in later chapters in this text. However, a few common anatomic variations of the frontal recess and frontal sinus deserve mention (Fig. 1.17). The agger nasi cell frequently forms the anteromedial aspect of the
floor of the frontal sinus. Agger nasi cells are quite common and are demonstrated on imaging in ~89% of patients.31 With significant pneumatization of the agger nasi cell, the frontal sinus outflow tract may be narrowed.5 On coronal CT scan imaging, an air cell may periodically be seen extending laterally over the superior orbital rim, at times giving the appearance of a septation in the lateral aspect of the frontal sinus.31,32 This cell, pneumatizing superolaterally over the orbit, is a supraorbital ethmoid cell. It is formed by ethmoid air cell pneumatization of the orbital plate of the frontal bone, and has been reported to occur in up to 62% of cases.5,23,31 Descriptions of the origins of the frontal sinus by Kasper attributed the derivation of supraorbital ethmoid cells to the third and fourth frontal furrows.16 Stammberger described the supraorbital ethmoid cell as originating from the sinus lateralis or suprabullar recess and pneumatizing over the roof of the orbit.4 On endoscopic visualization of the frontal recess, the ostium of the supraorbital ethmoid cell is located posterior and lateral to the internal frontal sinus ostium.32 Although significant anatomic variation may occur in the region of the frontal sinuses, the right and left frontal sinuses are typically separated by a thin bony partition called the frontal intersinus septum. Frequently, the right and left frontal sinuses are asymmetric in size, with the frontal intersinus septum oriented toward one side. At times, the frontal intersinus septum may be pneumatized, forming an intersinus septal cell.31,33 By carefully tracing the drainage path of a frontal intersinus septal cell on preoperative imaging, the sinus surgeon will often be able to determine that these cells drain unilaterally into the right or left frontal sinus but occasionally may have a separate ostium that drains directly into the frontal recess.31
Fig. 1.17 Illustration of the frontal sinus and frontal recess anatomic variations. Coronal representation of various frontal sinus and frontal recess variations. M, maxillary sinus; F, frontal sinus; AN, agger nasi cell; 14, type 14 frontal cells; SOE, supraorbital ethmoid cell; I, frontal intersinus septal cell
Frontal cells were broadly described in 1941 by Van Alyea as cells that impinged on the frontal recess and frontal sinus ostium.34 Currently, the most widely accepted classification of frontal cells was delineated by Bent et al.35 According to this classification, a type 1 frontal cell is a single anterior ethmoid air cell located superior to the agger nasi cell, which does not pneumatize into the frontal sinus. Type 2 frontal cells are multiple tiered anterior ethmoid cells superior to the agger nasi cell, and a type 3 frontal cell is a single large anterior ethmoid cell superior to the agger nasi cell, which extends into the frontal sinus and has a connection to the frontal recess. Finally, a type 4 frontal cell is an anterior ethmoid cell that appears to be completely contained within the frontal sinus and attached to the anterior table of the frontal sinus. By definition, types 1 to 4 frontal cells have bony connections with the anterior frontal recess or anterior table of the frontal sinus; there are no bony connections to the posterior table of the frontal sinus or the skull base.31,35
The frontal recess and frontal sinus present some of the greatest challenges to the sinus surgeon. This chapter presents some of the basic anatomy and anatomic variations present in this intricate area. Knowledge of the frontal recess, agger nasi and supraorbital ethmoid cells, frontal intersinus septal cells, and frontal cells form the basis for understanding this complicated area. However, the varied pneumatization and complexity of the frontal recess and frontal sinus cannot be overstated and often remains challenging, even for the most experienced sinus surgeons. We direct the reader to later chapters in this text devoted to surgery of the frontal sinus for additional discussion of the complex anatomy of the frontal recess and frontal sinus.
Positioned in the most posterior medial location of all the paranasal sinuses, the sphenoid sinuses sit at the central skull base. The sphenoid sinus drains through its natural ostium into the sphenoethmoid recess. The sphenoid ostium is located on the face of the sphenoid sinus in an anterior superior location with respect to the sinus itself, and is traditionally taught to be 7 cm at a 30-degree angle from the nasal spine in the adult. On visualization of the face of the adult sphenoid sinus, the sphenoid ostium is typically located ~1.0 to 1.5 cm above the superior aspect of the posterior choana and sphenoid sinus floor, and lies between the nasal septum and the posterior insertion of the superior or supreme turbinate.36 The roof of the sphenoid sinus, comprising the sphenoid skull base, is termed the planum sphenoidale. In the posterior superior aspect of the sphenoid cavity, a rounded bony projection may be seen when the sphenoid sinus is well pneumatized. This area is the bony covering over the pituitary gland, called the sella turcica. Inferior to the sella turcica is the thick bone of the clivus that forms the posterior inferior wall of the sphenoid sinuses. The sphenoid rostrum forms the face and the floor of the sphenoid sinuses and articulates anteriorly with the vomer bone. In some cases, the inferior lateral aspects of the sphenoid sinuses will be pneumatized, forming lateral pterygoid recesses. In cases of spontaneous cerebrospinal fluid leak, skull base defects are often found in these pneumatized lateral recesses of the sphenoid sinus and specialized trans-pterygopalatine fossa surgical approaches may be needed to address cerebrospinal fluid leaks in this location.37 As seen in the frontal sinuses, a sphenoid intersinus septum divides the right and left sphenoid sinuses. It is quite common for the right and left sphenoid sinuses to develop asymmetrically and exhibit different size and pneumatization patterns in the adult. In planning and undertaking surgery of the sphenoid sinuses, the sphenoid intersinus septum must be carefully evaluated. The sphenoid intersinus septum may be deviated unilaterally, and in such cases, may insert in the vicinity of one of the surrounding vital structures, such as the internal carotid artery or optic nerve.5 In a similar manner to the frontal intersinus septum, the sphenoid intersinus septum may also have some degree of pneumatization. Incomplete sphenoid septations may be noted as well. The paranasal sinus surgeon must remain mindful of critical anatomic structures surrounding the sphenoid sinus (Fig. 1.3). The pituitary gland lies posterior and superior to the sphenoid cavity at the midline, just below the optic chiasm. The optic nerves and internal carotid arteries may be seen as bony impressions on the walls of the sphenoid sinus in the lateral, posterior, and superior position. In the well pneumatized sphenoid, a bony indentation representing the opticocarotid recess may be seen between the optic nerve and carotid artery impressions. The cavernous sinus is located lateral to the sphenoid sinus lateral wall, with the third through sixth cranial nerves and internal carotid artery traversing through it. The vidian nerve is located in an inferolateral position. In highly pneumatized sphenoid sinuses, the vidian canal may be seen running in an inferior lateral position along the sphenoid sinus floor toward the internal carotid artery. In radiologic analysis of the intrasphenoid optic canal, Batra et al. determined that the sphenoid most commonly pneumatized to the level of the optic canal (39.8%), with the optic nerve creating an indentation on the lateral wall of the sphenoid sinus.22 However, in up to 15.6% of sphenoid sinuses and 8.3% of sphenoethmoid cells, the optic nerve was seen freely traversing these air cells. In addition, in 30.5% of cases, the intersinus septum inserted directly onto the optic nerve canal, and in 12.5% of cases, optic nerves were frankly dehiscent of bony covering. In a similar study of the carotid canal, the retrosellar internal carotid artery segment was found to have 90 to 180 degrees of adjacent sphenoid sinus pneumatization in 50% of cases.14 Furthermore, in 37.5% of cases, the sphenoid intersinus septum inserted directly onto the bony carotid canal, and in 19.5% of cases, the internal carotid arteries were dehiscent. These findings highlight the
importance of careful preoperative planning and analysis of imaging studies, due to the proximity of critical structures surrounding the sphenoid sinus.
This chapter presents an overview of the prenatal and postnatal development of the paranasal sinuses, followed by a summary of sinonasal anatomy. Although an understanding of the anatomic principles and relationships outlined in this chapter will assist the sinus surgeon in approaching sinonasal pathology, sinus surgeons should bear in mind that paranasal sinus pneumatization patterns may vary significantly. There is great potential for significant differences in sinonasal anatomy from patient to patient, and even between the right and left sides within the same patient. Therefore, close study of preoperative imaging and knowledge of individual patient anatomy is imperative to prevent complications during paranasal sinus surgery.
2 Sinonasal Physiology
David A. Gudis, Bradford A. Woodworth, and Noam A. Cohen The external nose and nasal cavity represent a critical unit whose function is to cleanse and humidify inspired air, as well as sample it for olfaction. The function of the surrounding paranasal sinuses is less clearly understood, but hypothesized to lighten the sku ll and generate a crumple zone for protection of the brain and eyes from facial trauma. Additionally, the sinonasal unit is the initial contact point for many environmental insults ranging from simple pollution to complex infectious agents. Thus, each structure and region within the sinonasal cavity represents a tier of defense and protection against the external environment.
Protection of the Upper Airway
As air is inspired through the nose, it immediately encounters the first of many protective features of the sinonasal cavity: the vibrissae. The vibrissae are coarse hairs whose follicles are located just within the nasal meatus. They filter large aerosolized particulate matter from inspired air, and they are aided in expelling the debris by the sweat and sebaceous glands in the stratified squamous epithelium of the anterior nares, the only squamous epithelium of the sinonasal cavity. Vibrissae are present in most mammals, but their innervation and role in sensory function appears to be less pronounced in humans. Just beyond the meatus of the anterior nares and vibrissae, inspired airflow is regulated by the nasal valves, the next tier of sinonasal defense. The external nasal valve is defined by the angle between the lateral crus and the medial crus of the lower lateral cartilage, the columella, and the nasal sill. The internal nasal valve the narrowest segment of the upper airwayis defined by the angle between the caudal upper lateral cartilage, the septum, the anterior face of the inferior turbinate, and the nasal floor. Both valves are dynamic such that they limit airflow at variable rates. When the velocity of inspired air increases with forceful inspiration, the pressure of the air passing through the nasal valves decreases relative to the ambient air outside the nasal valve in accordance with the Bernoulli principle of fluid dynamics. This pressure differential causes the nasal valve to decrease in aperture, varying with respect to the individual size, shape, and soft tissue compliance of a particular nose. During times of labored breathing or exercise, the alar muscles contract to dilate the nares to oppose the effect of this air pressure differential. This mechanism allows the nasal valves to ensure that air is not inspired faster than it can be warmed, humidified, and cleaned.
The Turbinates
Inspired air then encounters the turbinates of the nasal cavity. The three shelflike structures project from the lateral wall of the nasal cavity toward the septum and provide a crucial protective function of the sinonasal cavity. The superior and middle turbinates are extensions of the ethmoid bone, whereas the inferior turbinate is an independent osseous structure. Most air passes between the middle and inferior turbinates, with a maximum velocity just posterior to the internal nasal valve.1 By increasing the total surface area of the nasal cavity, the turbinates significantly contribute to warming and humidifying inspired air. At respiratory rates of up to 7 L per minute, the nasal airway can warm air to 37C from ambient temperatures as low as 25C and maintain the humidity of inspired air at ~85% within a wide range of ambient environmental humidity.2 This controlled temperature and humidity of air entering the lungs facilitates pulmonary alveolar gas exchange. The orientation and shape of the turbinates streamlines inspired air posteriorly toward the nasopharynx while providing sufficient obstructive resistance to change the airflow from a laminar to a transitional pattern. Additionally, the cross-sectional area of the nasal airway increases substantially just past the nasal valves, leading to a drop in airflow velocity just before the air reaches the turbinates; this too contributes to the loss of laminar airflow.2 Transitional airflow is neither completely laminar nor completely turbulent, and its dynamics are protective in several ways. The element of turbulence causes much of the aerosolized debris, including pathogens and dust, to precipitate from inspired air and land in the mucus layer of the epithelium. The change in airflow pattern also exposes more air molecules to the warm and moist mucosa of the large
turbinates, whereas a laminar flow would shield a central column of air from the mucosa. However, a completely turbulent flow with no laminar component would be undesirable because it would generate higher resistance and lower velocity of the airflow in the nasal passage. Such turbulence becomes useful only during the sniff, the mechanism of olfactory detection whereby quick high-flow (>300 mL/s per nostril) inhalation generates enough turbulence to expose more odorants to the olfactory mucosa, tucked posterosuperior to the superior turbinate.3 Therefore, the transitional airflow pattern of normal breathing balances the protective features of turbulent flow with the lower resistance of laminar flow. When nasal resistance is too low, however, patients may paradoxically report subjective complaints of obstruction or difficulty breathing, known as empty nose syndrome. The turbinates may provide u p to 50% of total airway resistance when one breathes nasally. Thus, after excessive surgical turbinectomy, the altered velocity differentials and resistance patterns throughout the upper airway may result in a paradoxical nasal obstruction, with patients reporting shortness of breath and unsatisfying breathing.4 These clinical sequelae demonstrate the functional importance of turbinates to effectively create a unique transitional airflow pattern that is necessary to protect the upper airway while allowing for normal and comfortable breathing. Nasal air filtration proves to be remarkably efficient. Humans inspire between 10,000 and 20,000 L of air per day. About 80% of particles 3 to 5 m in diameter and 60% of particles 2 m in diameter are filtered by nasa l filtration, with the vast majority of this filtration process occurring anteriorly. Studies with radiolabeled water have found that ~95% of pollen-sized particles are trapped in the anterior nasal cavity.5 However, despite this powerful filtration system, countless contaminants including particulate debris and infectious pathogens pass through to the upper airway and become trapped in the mucus layer of the sinonasal epithelium, generally allowing only particles less than 1 m to pass into the lungs. Muco ciliary clearance is the process by which the mucus layer containing such debris is transported to the gastrointestinal tract for elimination, and it is the definitive mode of defense for both the upper and lower airways.
The Nasal Cycle
In the anatomically normal nasal airway, most people experience asymmetric airflow through the nose. At any time, one nasal passage is typically more widely patent to airflow and has increased secretions from both serous and mucus glands, whereas the other passage is more congested with reduced secretions.2 This feature of the nasal airway, known as the nasal cycle, is tightly regulated by a combination of neural control and vasomotor input that results in alternating engorgement and constriction of the arterioles, precapillary sphincters, and most significantly, the venous sinusoids within the erectile mucosa of the nasal passage. The mechanisms governing these vascular changes are not completely understood, but vascular tone is influenced by factors including local metabolic and vasoactive substances, neurotransmitters, and neuropeptides (Table 2.1).This erectile tissue is most fully developed along the anterior nasal septum and on the inferior turbinates, but is distributed throughout much of the nasal airway. At peak congestion, the mucosal edge of the inferior turbinate may protrude anteriorly as far as 5 mm beyond its baseline decongested position.6 Sympathetic adrenergic input leads to constriction of the vasculature and a patent nasal passage, which plays an additional role in increasing systemic oxygenation in the fight-or-flight response. Parasympathetic input may contribute to vasodilatation and engorgement of the distensible mucosa but appears to play a much smaller role in this process. Rather, parasympathetic input to the sinonasal cavity functions largely to stimulate glandular secretions.7 Table 2.1 Endogenous Vasoactive Substances on Nasal Mucosa
The nasal cycle has been described as far back as 1895, when Kayser found that patients had varying airway resistance in each nasal passage, yet a constant total resistance of the whole nasal airway.8 Some investigators have found using rhinomanometry that ~80% of normal people undergo this recurring process, and that the patent and congested sides alternate every 2 to 7 hours on average.7 However, the term nasal cycle has been called into question, as there is little data to confirm that a consistent rhythmic periodicity exists that predicts the alternating patency and congestion of a nasal passage. Rather, it is now commonly accepted that most people exhibit an irregularly alternating patency and congestion governed by many factors including posture, infection, mucosal irritants, hormones, temperature, and drugs. Kayser was still correct in his original estimation that, despite changing resistance of individual nasal passages, the total resistance of the combined nasal cavities remains largely unchanged,8 and because there is often no sensation of obstruction from the congested side, the cycle goes unnoticed by most people. The functions of the nasal cycle are not entirely understood, but it most likely serves both mechanical and immunologic roles. The cycles mechanical functions include augmenting the efficacy of the turbinates to humidify and warm inspired air. During inspiration of cold or dry air, the blood is directed through the capillaries and venous sinusoids leading to engorgement of the erectile tissue and swelling of the nasal lining. Additionally, the nasal cycle may play a role in controlling nasal secretions, whereby the alternating congestion and decongestion creates a pump-like mechanism for plasma transudate, an important component of these secretions. During the period of decongestion, the increased sympathetic tone that constricts the venous sinusoids of the erectile tissue may raise their intravascular hydrostatic pressure, resulting in increased plasma filtration through the endothelium of the distensible venous sinusoids in the nasal lining.9 This plasma transudate, as a component of nasal secretions, has been suggested to play a major role in the first line of defense against pathogenic organisms that enter the nose as the primary site of infection. Indeed, studies have confirmed that the amplitude of the nasal cycle as measured in unilateral nasal resistance is increased during acute viral upper respiratory infections,8 supporting the immunological role of the nasal cycle. The system of neural and humoral factors that control the nasal mucosa is complex and includes adrenergic and cholinergic fibers as well as vasoactive intestinal peptide and nitric oxide, where parasympathetic input causes engorgement and congestion and sympathetic input causes constriction and patency (Table 2.1). Most nasal decongestants are selective alpha agonists that cause precapillary vasoconstriction with selective shunting of blood through the arteriovenous anastomoses, leading to decreased nasal edema.
The Sneeze Reflex
The sneeze reflex is a protective mechanism that causes a forceful nasal expulsion of air and secretions in response to an irritating or noxious stimulus. It protects the upper airway in a manner analogous to the cough reflex of the lower airway. The function of this reflex is to expel the offending irritant from the nasal cavity. The velocity of exhaled air associated with a sneeze may reach in excess of 100 miles per hour.10 Thus, the sneeze is a highly effective neuromuscular response involving both cranial and spinal nerves. Although the exact neural arcs are unknown, certain neurological deficits have been described that lead to an impaired sneeze reflex. While the olfactory nerve conveys the specialty olfactory senses (and is discussed in detail in Chapter 4), the trigeminal nerve conveys thermal, noxious, and mechanical stimuli from the nasal cavity. When an irritant is present in the nose, the sneeze reflex is initiated through activation of the afferent fibers of the trigeminal nerve (V1 and V2). The efferent parasympathetic fibers, carried from the pterygopalatine ganglion, then stimulate the corresponding mucosa to increase local secretions, the initial effort to flush or dislodge the irritant. Simultaneously, the phrenic nerve stimulates the diaphragm to activate inspiration. Then, the anterior abdominal wall muscles are stimulated to contract, generating a powerful exhalation. Concurrently, the glossopharyngeal and vagus nerves elevate the palate and contract the superior pharyngeal constrictor, causing a brief Valsalva maneuver, before forcing the pressurized exhalation through the nasal cavity. In cats, a sneeze center has been localized to the lateral medulla, the brainstem region containing the glossopharyngeal and vagus nerve nuclei.11 It has been suggested that an analogous region exists in humans. Wallenberg syndrome is a relatively common manifestation of ischemic insult to the lateral medulla caused by vertebral or posterior inferior cerebellar artery occlusion. Indeed, there have been several case reports of patients with Wallenberg syndrome who have an impaired sneeze reflex.12 Such patients describe the
sensation of the urge to sneeze, but no spontaneous forced nasal expulsion ensues. This complaint corresponds to their neurological deficit of impaired motor function from the glossopharyngeal and vagus nerve nuclei despite intact sensory function of the trigeminal nerve and nucleus, providing evidence that humans may have a localized brainstem center for the sneeze reflex as well.
The Mucosa, Mucus, Cilia, and Mucociliary Clearance
The Mucosa When aerosolized pathogens and debris pass through the initial tiers of nasal defense and are greater than 0.5 to 1 m, they become trapped in the mucus layer of the sinonasal mucosa. The sinonasal mucosa protects the cavities and upper airway from inhaled pathogens, toxins, and debris by mucociliary clearance, a specialized function of the unique protective epithelium of the airway. Mucociliary clearance, which comprises mucus production and mucus transport, removes both healthy secretions and pathological debris from the sinonasal airway. Although the cough and sneeze mechanisms may supplement mucus clearance from the lung and nose respectively, mucociliary clearance remains the principal mode of defense of the respiratory system, especially of the paranasal sinuses. The mucosa consists of a superficial layer of epithelium with variable numbers of goblet cells, an acellular basement membrane, a thick lamina propria containing vascular and glandular layers, and the periosteum (Fig. 2.1). The epithelium of each part of the nasal cavity is specialized to suit its particular region. The anterior margin of the nasal vestibule is composed of stratified squamous epithelium. Containing sebaceous glands, sweat glands, vibrissae, and finer hair, the stratified squamous epithelium provides a protective barrier much like the skin of the rest of the face. Around the area of the nasal valves, the stratified squamous epithelium transitions to the pseudostratified columnar ciliated epithelium found throughout the rest of the nasal cavity (with the exception of the olfactory epithelium). This region of epithelial transition, which is 1 to 2 mm in thickness, overlies dense arterial anastomoses. The anastomoses lead to a plexus of capillaries derived from the anterior ethmoid, greater palatine, sphenopalatine, and superior labial arteries. This plexus, known as Kiesselbachs or Littles area, is believed to be the source of 80% of epistaxis, owing to its rich blood supply and anterior location.13 The transitional area between stratified squamous epithelium and pseudostratified columnar ciliated epithelium enlarges as a person ages. As the most anteroinferior columnar epithelium is exposed to years of desiccation from inspired airflow, it may undergo squamous metaplasia, a common adaptive mechanism of stressed epithelium. The total surface area of intranasal squamous epithelium thus often increases over the course of ones life.
The respiratory mucosa of the remainder of the sinonasal cavity and turbinates consists of columnar epithelium (~80%), goblet cells (~20%), and basal cells (less than 5%). Although the nasal columnar epithelium is predominantly pseudostratified, including both ciliated and nonciliated cells, the paranasal sinus columnar epithelium is predominantly simple ciliated columnar cells.1 Both ciliated and nonciliated columnar cells have hundreds of immotile microvilli along their surface, tiny hairlike projections of actin filaments 1 to 2 m in
length covered by the cell membrane. The microvilli tremendously increase the total surface area of the columnar cells, which likely aids the sinonasal mucosa in mucus production, secretion, and sensation.14 The goblet cells, interspersed throughout the columnar cells, contribute to mucus production via secretory granules that contain mucina glycoprotein essential to the viscosity and elasticity of mucus. The apical surface of a goblet cell is also covered with microvilli and has a small duct through which it releases its secretions into the nasal cavity (Fig. 2.2). Basal cells, attached to the basement membrane by hemidesmosomes, are shielded from the abrasive and contaminated environment of the nasal cavity and paranasal sinuses. In addition to serving as a progenitor cell that can differentiate into goblet or ciliated columnar cells, basal cells may also aid in anchoring the overlying columnar cells to the basement membrane.15The epithelium of the sinonasal mucosa is constructed with three types of intercellular junctions. Adherens junctions, comprised of actinlike filaments, bind epithelial cells to their basement membrane with protein structures including hemidesmosomes, macula adherents, and zonula adherents (Fig. 2.3). Tight junctions surround each epithelial cell and ensure that the epithelial layer remains impermeable to water molecules, ions, and potential pathogens. Finally, gap junctions provide small windows connecting the cytoplasm of adjacent epithelial cells. They allow certain ions and charges to pass through and likely play an important role in ciliary coordination.16
Beneath the thin basement membrane lies the lamina propria, the layer containing the glands, vasculature, and nerves supplying the sinonasal mucosa. The lamina propria has a superficial glandular layer, a vascular layer, and a deep glandular layer. Anterior serous glands, present on the anterior septum and lateral nasal wall, produce a watery secretion that contributes to the moisture of the nasal cavity. Seromucinous glands are found throughout the cavity and contribute a combination of serous and mucinous secretions. Intraepithelial glands consist of several goblet cells arranged around a lumen and contribute a small amount of mucus to nasal secretions. The parasympathetic fibers that course throughout the lamina propria originate in the superior salivatory nucleus of the brainstem and are carried by the nervus intermedius branch of the facial nerve to the greater superficial petrosal nerve. The sympathetic fibers of the nasal mucosa originate in the sympathetic trunk, synapse in the superior cervical ganglion, and are carried by the deep petrosal nerve. The greater superficial petrosal and deep petrosal nerves then join to form the vidian nerve, which carries the autonomic nervous supply through the pterygopalatine ganglion, where parasympathetic fibers synapse, and the autonomic fibers are then carried to the mucosa by the trigeminal nerve (V2). The parasympathetic fibers of the lamina propria directly stimulate glandular secretions and can be blocked by atropine or other anticholinergics. The sympathetic fibers of the lamina propria, as mentioned, appear to play a more significant role in mucosal vasoconstriction and decongestion than in regulating nasal secretions.15 The Mucus The epithelium is covered in a mucus blanket that traps cellular debris, pathogens, and particulate matter that precipitates from inspired air. Mucus consists of two layers: the gel phase is a discontinuous outer viscous layer that rides along the tips of extended cilia; and the sol phase surrounds the shafts of cilia as a continuous inner layer of lower viscosity composed of water and electrolytes (Na1, K+, Ca2+, Cl2). Mucus is an immunologically active substance composed of water (~95%), proteins and peptides (2 3%), salts (1%), and debris (1%), with a slightly acidic pH of 5.5 to 6.5.17 Its fluid content includes varying concentrations of plasma exudate, submucosal and goblet cell secretions, tears and lacrimal gland secretions, and serous secretions from the olfactory glands of Bowman. Approximately 600 to 1,800 mL of mucus is produced by the sinonasal mucosa per day.17 Mucin proteins, secreted by goblet cells, are a group of large threadlike glycoproteins that contain peptide backbones and oligosaccharide side chains. They are an essential component of mucus that give the gel phase its characteristic rheologic properties of viscosity and elasticity. They are secreted in condensed form and undergo hydration to form a gel, which facilitates mucociliary clearance by creating a unique fluid structure that can retain trapped debris while maintaining a pliable and easily transported medium. The mucin proteins themselves may also play an important role in host defense. Their carbohydrate side chains appear to bind surface adhesins on microorganisms, and recognition sites on side chains have been described for adhesins of Mycoplasma pneumoniae, Streptococcus pneumoniae, Pseudomonas aeruginosa, influenza virus, and Escherichia coli.18 Therefore, mucin-associated carbohydrates may serve an additional protective mechanism by strongly binding and effectively clearing microorganisms that frequently colonize the upper airways. Mucins may also bind other endogenous proteins within the mucus, including lysozyme and lactoferrin, to protect and structurally support these molecules and facilitate their role in host defense.19 Furthermore, activated neutrophils, which are central to the acute inflammatory response, stimulate mucin secretion by goblet cells. Mucus contains many proteins that aid in the local immune defense of the mucosal layer, including the innate immunity proteins lysozyme, lactoferrin, antitrypsin, and surfactant proteins. Lysozyme is a protective enzyme that catalyzes the hydrolysis of bacterial cell walls, and is more effective against Gram-positive bacteria. Lactoferrin is a multifunctional protein with a very high iron affinity that has antimicrobial and immune modulatory activities. By strongly binding iron, lactoferrin deprives local bacteria and fungi of this essential growth nutrient. Lactoferrin may also directly damage the cell wall of Gram-negative bacteria by causing the release of lipopolysaccharides, which are essential to the structural integrity and protective membrane of bacteria.15 Collectin (collagen-lectin) proteins, such as surfactant proteins (SP-A and SP-D) and mannosebinding protein, exhibit antimicrobial properties and interact with numerous bacteria such as Staphylococcus species, Streptococcus species, Klebsiella pneumoniae, P. aeruginosa, E. coli, Aspergillus, Mycobacterium tuberculosis, and Salmonella species.20 These bacteria have related molecular structures called pathogenassociated molecular patterns (PAMP) that consist of polysaccharides and polynucleotides, such as lipopolysaccharide (LPS). PAMPs differ little from one pathogen to another, but are not found in the host.
Collectins bind PAMPs located on microbial membranes via their calcium-dependent carbohydrate-binding domains that promote bacterial clearance.2123 Immunoglobulin A (IgA) and IgG, produced mostly in the mucosa-associated lymphoid tissue (MALT) of the inferior and middle turbinates, are protective antibodies that further augment the defensive barrier of mucus. IgE, which plays a central role in the allergic response (discussed later in text), and IgM are also present in nasal secretions but in lower concentrations. IgA is the major antibody of secretions and mucosal defense, and selective IgA deficiency may result in recurrent sinopulmonary infections. Indeed, IgA deficiency is the most common Ig deficiency responsible for recurrent sinonasal infections.24 IgA opsonizes pathogens to facilitate their phagocytosis by macrophages and neutrophils, and the aggregation of IgA activates the complement pathway of defense. In concert with lysozyme and complement, IgA also has more specific bactericidal effects against certain pathogens like S. pneumoniae.25 IgG is also very effective at opsonizing pathogens for phagocytosis and activating the complement pathway but plays a less significant role in mucosal secretions. Dendritic cells support the innate immunity of the sinonasal mucosa by processing mucosal antigens and presenting them to T cells, which then engage B cells, in the MALT.26 The composition of mucus, while variable, is essential to normal respiratory health, and disorders of mucus production can be debilitating. Cystic fibrosis (CF), an autosomal recessive disease resulting from a mutation in a single gene, involves several organ systems and is considered to be a disease of abnormal mucus production secondary to defective electrolyte transport. The genetic defect is found in the CF transmembrane conductance regulator gene product (CFTR), a cyclic adenosine monophosphate (cAMP)-mediated membrane glycoprotein that forms a chloride channel but also intimately regulates the open probability of the sodium channel, ENaC. The movement of intracellular water from the endothelium into the extracellular mucus layer is an osmotic process that follows electrolyte concentrations, so these patients with defective sodium chloride transport develop abnormally viscous mucus. The goblet cells in such patients subsequently become very engorged and distended. These patients have severely impaired mucociliary clearance and frequently develop severe recurrent sinopulmonary infections.22 The Ciliary Structure and Function Respiratory cilia clear the mucus blanket containing pathogens and debris from both the upper and lower respiratory passages by beating in a coordinated and rhythmic manner. Cilia are cylindrical organelles protruding from the apical surface of epithelial cells and are anchored by intracellular basal bodies derived from centrioles. There are ~50 to 200 cilia per epithelial cell, each measuring 5 to 7 m in length and 0.2 to 0.3 m in diameter.17 Each cilium is composed of a bundle of interconnected microtubules, termed t he axoneme, and an overlying membrane that is part of the cell plasma membrane. Microtubules are made of protofilaments, which in turn are composed of alpha-and beta-tubulin dimers. The major beta-tubulin in cilia is the type IV isotype,27 which is much more abundant in the cilia than elsewhere in the cell and makes for an ideal marker for respiratory cilia in the research setting (Fig. 2.3). The axonemes of motile cilia contain two central singlet microtubules surrounded by nine doublet microtubules (Fig. 2.4). Each doublet consists of one alpha-tubule, a complete circle of 13 protofilaments, and one betatubulean incomplete circle of 10 protofilaments. This axoneme structure is preserved across the motile cilia of the respiratory epithelium, the oviduct, and the ventricular ependymal cells. The two central microtubules are attached by paired bridges, whereas the peripheral doublets attach to the central pair via radial spoke heads. Each outer doublet interacts with the adjacent outer doublets via inner dynein arms (IDA), outer dynein arms (ODA), and nexin, each having a distinct role in the dynamic motion of cilia bending.28 Activation of the dynein arms generates a sliding motion of one microtubule doublet against the adjacent doublet. In the Chlamydomonas, phosphorylation of the ODAs regulates cilia beat frequency while phosphorylation of the IDAs regulates the wave form pattern of beating.29 Although the function of the radial spoke heads is not entirely understood, it seems they are involved in regionally limiting the sliding between the microtubules during the ciliary stroke, thus converting the sliding motion generated by the dynein arms into a bending motion of the axoneme.30
Each cilium has a forward power stroke followed by a recovery stroke. During the power stroke, the cilium is fully extended, and at the apogee of the arc, the distal tip makes contact with the viscous outer mucus layer (gel phase), thereby transmitting directional force to the overlying mucus blanket. During the recovery stroke, the cilium bends 90 degrees and sweeps back to its starting point within the thinner periciliary fluid layer (the sol phase). The mechanism of ciliary motion depends on a series of ATP-dependent molecular motors that cause the outer doublets of the axoneme to slide relative to each other, producing a vectorial force. The central pair of microtubule singlets divides the axoneme into two opposing halves. As proposed by the switch point hypothesis, the dynein motors on one side of the axoneme are predominant ly active during the effective stroke, whereas the motors on the other side are mainly active during the recovery stroke. If the microtubules are numbered in a clockwise fashion from 1 to 9, the effective stroke would involve the ODAs on the 9 1-23-4 microtubules, and the recovery stroke would involve activity of the dynein in the 5 6-78 microtubules.31 The dynamic force of each power stroke is directly proportional to the number of dyneinmicrotubule interactions,32 and there is usually a physiologic reserve available to increase the force of the stroke when necessary.33 The orientation of the stroke is determined by the orientation of the anchoring basal body of the axoneme (Fig. 2.5).34 Although it is well established that cilia beat in a coordinated fashion, referred to as a metachronous wave, the mechanism of coordination is not entirely understood. One theory to explain the coordinated wavelike motion of cilia is that gap junctions connecting adjacent epithelial cells may allow a directional propagation of intracellular calcium waves driving the microtubule interactions and, ultimately, the entire metachronous wave.35 Another possible mechanism relies on the close relationship between the cilia and the hydrodynamic forces surrounding them in their partly liquid environment, where only a relatively small number of coordinated cilia would be necessary to generate a hydrodynamic wave that, in turn, forces the timed coordinating beating of nearby cilia.36 Once a metachronous wave is established, spontaneous beating can range from ~9 to 15 Hz in humans, and the cilia tip reaches a velocity of 600 to 1,000 m/s. The resultant dynamic range of mucus velocity is ~50 to 450 m/s, or 3 to 25 mm/min. The power and speed of the cilia results in a highly efficient mechanism that can clear the mucus blanket of the entire nose or sinus in 10 minutes.37
Ciliary beat frequency (CBF) changes in response to several chemical,38,39 thermal,40,41 mechanical,42 and hormonal4345 stimuli. Small changes in both extracellular and intracellular pH can have a profound impact on CBF. An increase in intracellular pH produces an increase in CBF, whereas a decrease in pH produces a decrease in CBF.46 However, it is not known whether this effect is due to modulation of kinase activity, even though an acidic pH has been demonstrated to inhibit PKA function,47 or by directly regulating the outer dynein arms of the axoneme.48 Ciliary beat frequency has also been shown to vary directly with respect to temperature, with the ideal temperature for CBF to be from 32 to 37C.40,41,49 Furthermore, direct mechanical stimulation of the cilia promotes an increase in CBF, which coincides with an increase in intracellular Ca2+.42 This mechanical stimulation is then propagated to the neighboring cells by diffusion of IP3 through gap junctions, which then activates a release of calcium from the intracellular pools. The end result is an increase in CBF in the entire region surrounding the site of mechanical stimulation.50 Extracellular nucleotides (adenosine and uridine) are especially potent regulators of epithelial functions and can stimulate mucociliary clearance in several ways. These nucleotides are released by local epithelium in response to mechanical and osmotic stimuli and act in a paracrine fashion.51 Through both metabotropic and ionotropic receptors, the nucleotides increase mucus secretion, increase CBF, and gate ion channels involved in maintaining epithelial surface liquid volume.52 This capability generates a tremendous reserve for dynamic regulation of mucociliary clearance when the respiratory system is environmentally challenged. Furthermore, adrenergic,45,53,54 cholinergic,55,56 and peptidergic57,58 stimulation have also been demonstrated to stimulate ciliary motility. These environmental and host stimuli are transmitted via surface receptors and channels to trigger activation of second messenger cascades that regulate phosphorylation status of ciliary proteins, thereby modulating the kinetics of microtubules sliding relative to each other. Inositol triphosphate (IP3)-mediated calcium transients have been correlated with increased CBF.59 61 Additionally, protein kinase A (PKA),56,62 protein kinase G (PKG),63,64 and nitric oxide (NO) dependent mechanisms of CBF stimulation have been proposed.39,65,66 In contrast, activation of protein kinase C (PKC) appears to decrease CBF.58,67 Kinase anchoring proteins (AKAPs), kinases, and phosphatases have been demonstrated to be tightly associated with the axoneme, which may allow rapid control of ciliary activity.6870 The Sinonasal Mucociliary Clearance Patterns The remarkable ability of cilia to create coordinated, microscopic wave movements is equaled by their ability to macroscopically propel mucus in a directional, oriented fashion. The mucus of the paranasal sinuses is directed toward the nasal cavity, where it then travels to the posterior nasopharynx and is eventually ingested into the immunologically active gastrointestinal tract. Appreciation of the natural clearance patterns of the sinuses is critical for successful surgical intervention, especially the frontal sinus, as scarring of confluence regions may lead to mucus stasis. In the maxillary sinus, mucus must flow superomedially, against gravity, from the most inferior portion of the cavity. Propelled by cilia, the mucus courses upward along the walls of the antrum and medially across the sinus roof toward the natural ostium in the superior medial wall of the sinus, which drains into the ethmoidal infundibulum. The anterior ethmoid cells direct their mucus toward their individual ostia, then into the middle
meatus, whereas the posterior ethmoid cells direct their mucus toward the superior meatus and eventually into the sphenoethmoidal recess. The sphenoid sinus also drains through its natural ostium into the sphenoethmoidal recess. The mucus flow pattern in the frontal sinus appears to be unique in that it demonstrates both retrograde and anterograde motion. Mucus along the medial portion of the sinus is carried superiorly, away from the frontal ostium, and then laterally along the roof of the sinus. The mucus along the floor and the inferior portions of the anterior and posterior walls is then carried medially toward the frontal ostium, where it then drains into the frontal recess and the ethmoid infundibulum. The mucociliary flow from the anterior sinuses (frontal, anterior ethmoid, maxillary) converges at the ostiomeatal complex. From here, the mucus is carried along the uncinate process and inferior turbinate to the posterior nasopharynx, generally passing anteriorly and inferiorly to the eustachian tube orifice (Fig. 2.6). The mucociliary flow from the posterior sinuses (posterior ethmoid, sphenoid), however, tends to travel posterior and superior to the eustachian tube orifice toward the posterior nasopharynx. From the posterior nasopharynx, further ciliary motion and swallowing direct the mucus blanket into the gastrointestinal tract, where infectious pathogens are far less likely to survive and create infection. Upper respiratory infections, inflammation, mucosal swelling, and anatomical anomalies may disrupt the normal mucus composition or mucociliary clearance flow pattern. In such cases where obstruction occurs in key areas like the ostiomeatal complex or eustachian tube orifice, associated symptomatology commonly results. (Rhinitis and sinusitis will be discussed in detail later in the text.) However, ciliary motion can adapt to a dynamic landscape. For instance, cilia will transport the mucus blanket around irregularities such as septal spurs.
The Ciliary Dysfunction Mucociliary clearance is dependent on normal cilia function and mucus composition. Thus, disease states that compromise these essential modes of defense tend to result in impaired clearance of infectious pathogens and, ultimately, recurrent sinopulmonary infections. Primary ciliary dyskinesia (PCD), or immotile cilia syndrome, is an inherited disorder of dysfunctional cilia that manifests as severely impaired mucociliary clearance. PCD patients typically present with chronic airway and recurrent middle ear infections. Because embryonic nodal cilia, which are essential for the normal left-right asymmetry of visceral development, are likewise defective, ~50% of PCD patients have situs inversus.71 Many patients, both male and female, also suffer from infertility because both sperm motility and fallopian tube transport of ova depend on functional cilia. Kartagener syndrome is a subgroup of PCD marked by the triad of chronic sinusitis, situs inversus, and bronchiectasis. The inherited defect of Kartagener syndrome is in the dynein arms of axonemal microtubules, which may result in the absence of the ODAs, the IDAs, or both. Other subsets of PCD patients may demonstrate normal ciliary structure, but random ciliary orientation. Thus, despite normal motility, cilia function is ineffective and results in impaired mucociliary clearance.72
In addition to inherited pathologies, exposure to various environmental pathogens can also alter the normal mucociliary clearance system. Infectious organisms that can interfere with their hosts mucociliary defense have a survival advantage, and several have indeed adapted such mechanisms. Common bacterial pathogens such as Haemophilus influenzae, S. pneumoniae, Staphylococcus aureus, and Pseudomonas produce specific toxins to impair ciliary motion and coordination.73 Viruses responsible for common upper respiratory infections disrupt the microtubule function of ciliated columnar cells and change the viscosity of the surrounding mucus. Impairing the local defense system facilitates the infectious pathogens upper airway colonization. Chronic rhinosinusitis (CRS), affecting more than 35 million Americans of all ages,74 represents several distinct entities that are clinically indistinguishable. Although the mortality of the disease is low, the morbidity is high with CRS patients, demonstrating worse quality-of-life scores (for physical pain and social functioning) than those suffering from chronic obstructive pulmonary disease, congestive heart failure, or angina.75 Multiple etiologies contribute to the development of CRS, but a common pathophysiologic sequela is ineffective sinonasal mucociliary clearance, resulting in stasis of sinonasal secretions and subsequent chronic infection and/or persistent inflammation. Although the literature is contradictory regarding mucus viscosity76,77 and basal ciliary beat frequency76,78 in CRS, recent work has suggested that a subset of patients with CRS have a blunted ciliary response to environmental stimuli.79 Additionally, air-liquid interface cultures of respiratory epithelium from patients with CRS have demonstrated an increased transepithelial ion transport compared with normal cultures, thereby altering mucus viscosity and potentially contributing to the pathophysiology of the disease.80
The respiratory system is regularly exposed to altered environmental conditions as well as constantly bombarded by environmental pollutants, respiratory pathogens, and aerosolized toxins. Thus, the system has evolved multiple physiologic strategies to regulate inspired air flow resistance, temperature, and humidification, as well as tightly modulate its ability to protect and defend itself. Disruption of these physiologic processes secondary to host or environmental factors such as anatomic variations, genetic mutations, overwhelming environmental pollution, or frequent infections contribute to the development of chronic rhinosinusitis. Other chapters of this book address issues in the management of CRS, with each strategy aimed at restoring a disrupted sinonasal physiologic process.
Anatomical Terms Of Location
Human Head And Neck
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