MORPHOLOGYMalignantmesotheliomasareoftenprecededbyextensivepleural fibrosis and plaque formation, readilyseenoncomputedtomographyscans.Thesetumorsbegininalocalizedareaandovertimespreadwidely,eitherbycontiguousgrowthorbydiffuseseedingofpleuralsurfaces.Atautopsy,theaffectedlung typically is ensheathed by a layer of yellow-white, firm, variably gelatinous tumor thatobliteratesthepleuralspace(
Fig.13.48 ).Theneoplasmmaydirectlyinvadethethoracicwallorthesubpleurallungtissue,butdistantmetastasesareuncommon.Normalmesothelialcellsarebiphasic,givingrisetopleuralliningcellsaswellastheunderlyingfibroustissue.Inlinewiththispotential,mesotheliomasconformtooneofthreemorphologicappearances:(1)epithelial, inwhichcuboidalcellswithsmallpapillarybudslinetubularandmicrocysticspaces(thisisthemostcommonpatternandalsotheonemostlikelytobeconfusedwithapulmonaryadenocarcinoma);(2)sarcomatous, inwhichspindled,occasionallyfibroblastic-appearingcellsgrowinsheets;and(3)biphasic, havingbothsarcomatousandepithelialareas.
Fig. 13.48 Malignantmesothelioma.Notethethick,firm,whitepleuraltumorthatensheathesthisbisectedlung.
Acute infections of the upper respiratory tract are among the most common afflictions of humans, most frequently manifesting as the “common cold.” The clinical features are well known: nasal congestion accompanied by watery discharge; sneezing; scratchy, dry sore throat; and a slight increase in temperature that is more pronounced in young children. The most common pathogens are rhinoviruses, but coronaviruses, respiratory syncytial viruses, parainfluenza and influenza viruses, adenoviruses, enteroviruses, and sometimes even group A β-hemolytic streptococci have been implicated. In a significant number of cases (around 40%), the cause cannot be determined; perhaps new viruses will be discovered. Most of these infections occur in the fall and winter and are self-limiting (usually lasting for 1 week or less). In a minority of cases, colds may be complicated by the development of bacterial otitis media or sinusitis.
In addition to the common cold, infections of the upper-respiratory tract may produce signs and symptoms localized to the pharynx, epiglottis, or larynx. Acute pharyngitis, manifesting as a sore throat, may be caused by a host of agents. Mild pharyngitis with minimal physical findings frequently accompanies a cold and is the most common form of pharyngitis. More severe forms with tonsillitis, associated with marked hyperemia and exudates, occur with β-hemolytic streptococcal and adenovirus infections. Streptococcal tonsillitis is important to recognize and treat early, because of the associated potential for development of peritonsillar abscesses (“quinsy”) or for progression to poststreptococcal glomerulonephritis and acute rheumatic fever. Coxsackievirus A infection may produce pharyngeal vesicles and ulcers (herpangina). Infectious mononucleosis, caused by Epstein-Barr virus (EBV), is an important cause of pharyngitis and bears the moniker of “kissing disease”—reflecting a common mode of transmission in previously nonexposed individuals.