Clinical history: 34-year-old gentleman presents with a mass in the left parotid gland that had been stable for the last 2 years but recently increasing in size.
What is your diagnosis?
Discussion and answer
This is a case of a pleomorphic adenoma. Examination of the mass shows a well-circumscribed nodule that is pale yellow to yellow and has focal hemorrhagic areas. Histopathologic exam shows a well encapsulated mass composed of mainly 2 populations of cells. >80% of the cells are spindle-shaped and arranged in whorls with abundant basement membrane production. The cells are not overtly pleomorphic but have vesicular nucleus with prominent nucleoli and are positive for S100, CK7, SMA and vimentin indicative of myoepithelial differentiation. Interspersed among these are another population of cells within a myxoid stroma some of which are focally positive for EMA but negative for SMA and S100
suggesting myxoid differentiation. The tumor shows only rare Mib1 positive cells. The capsule is intact in all places and no signs of capsular invasion are seen, indicative of its benign nature. There is no evidence of vascular, lymphatic or perineural invasion. Intralesional hemorrhage may have contributed to the acute increase in size.