Fig. 15.6 Pleomorphicadenoma.(A)Low-powerviewshowingawell-demarcatedtumorwithadjacent,deeplystaining,normalsalivaryglandparenchyma.(B)High-powerviewshowingepithelialcellsaswellasmyoepithelialcellswithinchondroidmatrixmaterial.
Mucoepidermoid carcinomas are composed of variable mixtures of squamous cells, mucus-secreting cells, and intermediate cells. These neoplasms represent about 15% of all salivary gland tumors, and while they occur mainly (60%–70%) in the parotids, they account for a large fraction of salivary gland neoplasms in the other glands, particularly the minor salivary glands. Overall, mucoepidermoid carcinoma is the most common form of primary malignant tumor of the salivary glands.
MORPHOLOGYMucoepidermoidcarcinomascangrowaslargeas8cmindiameterand,althoughtheyareapparentlycircumscribed,theylackwell-definedcapsulesandoftenareinfiltrative.Thecutsurfaceispalegraytowhiteandfrequentlydemonstratessmall,mucinouscysts.Onhistologicexamination,thesetumorscontaincords,sheets,orcystslinedbysquamous,mucous,orintermediatecells.Thelatterisahybridcelltypewithbothsquamousfeaturesandmucus-filledvacuoles,whicharemosteasilydetectedwithmucinstains.Cytologically,tumorcellsmaybebenign-appearingorhighlyanaplasticandunmistakablymalignant.
Clinical course and prognosis depend on histologic grade. Low-grade tumors may invade locally and recur in about 15% of cases but metastasize only rarely and afford a 5-year survival rate of over 90%. By contrast, high-grade neoplasms and, to a lesser extent, intermediate-grade tumors are invasive and difficult to excise. As a result, they recur in 25% to 30% of cases, and about 30% metastasize to distant sites. The 5-year survival rate is only 50%.
•Sialadenitis(inflammationofthesalivaryglands)canbecausedbytrauma,infection(suchasmumps),oranautoimmunereaction.
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Pleomorphicadenomaisaslow-growingneoplasmcomposedofaheterogeneousmixtureofepithelialandmesenchymalcells.Itistypicallybenign.
Mucoepidermoidcarcinomaisamalignantneoplasmofvariablebiologicaggressivenessthatiscomposedofamixtureofsquamousandmucouscells.
Odontogenic cysts usually are derived from remnants of odontogenic epithelium present within the jaws. In contrast to the rest of the skeleton, epithelium-lined cysts are quite common in the jaws. These cysts are subclassified as either inflammatory or developmental. Only the most common lesions are considered here, starting with developmental cysts.
The dentigerous cyst originates around the crown of an unerupted tooth and is thought to be the result of degeneration of the dental follicle (primordial tissue that makes the enamel surface of teeth). They are lined by a thin, stratified squamous epithelium that typically is associated with a dense chronic inflammatory infiltrate in the underlying connective tissue. Complete removal is curative.