The visual pathways have now determined the site of the lesion.
Visual information from the temporal fields is projected onto the medial aspect of the retina bilaterally. The visual information from the medial aspects of the retina is carried in fibers that cross the midline through the optic chiasm to the opposite side.
The lesion is in the area of the optic chiasm.
Any disruption of the optic chiasm produces the field defect of bitemporal hemianopia. Tumors of the optic chiasm are unusual, though gliomas do occur. More frequently, compression of the optic chiasm by tumors in the vicinity is the usual cause for bitemporal hemianopia.
A pituitary tumor was diagnosed.
The optic chiasm is anterior and extremely close to the pituitary gland. Given that the patient is producing excessive amounts of prolactin (a pituitary tumor) and there is loss of the function of the chiasm, the most likely clinical explanation is an exophytic pituitary tumor compressing the optic chiasm.
An MRI scan was performed and demonstrated a large tumor (macroadenoma) of the pituitary gland.
Drug treatment was commenced and the tumor shrank (eFig. 8.295). The endocrinological effects of the prolactin secretion also stopped.
Follow-up scans were performed.
Over the ensuing few years the tumor shrank. Unfortunately, the patient again began to secrete prolactin and surgery was performed.
A transsphenoidal approach was undertaken.
With meticulous accuracy a series of very fine instruments was passed through the nasal cavity into the sphenoid bone. The bone was drilled and via this approach the pituitary gland was removed.
Extreme care must be taken because on both sides of the pituitary gland is the cavernous sinus through which the internal carotid artery, oculomotor nerve [III], trochlear nerve [IV], trigeminal nerve [V], and abducent nerve [VI] pass.
1121.e2 1121.e1
Fig. 8.7, cont’d Skull.
Conceptual Overview • Relationship to Other Regions
Fig. 8.16, cont’d
In the clinic—cont’d
In the clinic—cont’d
In the clinic—cont’d
In the clinic—cont’d
In the clinic—cont’d
Table 8.5 Cranial nerves (see Table 8.4 for abbreviations)—cont’d
In the clinic—cont’d
Table 8.7 Muscles of the face—cont’d
In the clinic—cont’d
In the clinic—cont’d
Fig. 8.149, cont’d
In the clinic—cont’d
Fig. 8.235, cont’d
Fig. 8.239, cont’d
Surface Anatomy • Visualizing Structures at the CIII/CIV and CVI Vertebral Levels
Surface Anatomy • How to Locate the Cricothyroid Ligament
Surface Anatomy • Major Features of the Face
Neuroanatomy and neuroscience are fields of science that seek to explain embryonic development, structural organization, and physiological function of the nervous system. Both fields work together to help identify the simple to the most complex questions of human sensory, motor, behavioral, and higher cognitive functions. The focus of this chapter is to introduce the basic structures and functions of the individual and systemic components of the human nervous system.
Part I: Nervous system
Organization of the human nervous system is structurally divided into the central nervous system (CNS) and peripheral nervous system (PNS) (eFig. 9.1). Components of the CNS are the brain and spinal cord, which are enclosed within the cranial cavity and vertebral column of the axial skeleton. Peripheral nervous system structures include cranial nerves, spinal nerves, autonomic nerves, and the enteric nervous system.