Lipomatous pleomorphic adenoma of the parotid gland. Classification of lipomatous tissue in salivary glands

Lipomatous pleomorphic adenoma is an unusual subtype with a lipomatous stro mal component of more than 90% of the tumour tissue. This special type of p leomorphic adenoma must be distinguished from other types of lipomatous tum ours or non-tumourous lipomatosis of the salivary glands. Until now only tw o cases of lipomatous pleomorphic adenoma have been reported in the literat ure. We report of a 36-year old woman who developed a well circumscribed no dule measuring 3,5 x 2,5 x 2 cm in the right parotid gland. The cut surface was grey-yellowish. Histologically, more than 90% of the tumour tissue was fatty tissue with univacuolar adipocytes. The pleomorphic epithelial eleme nts were duct-like cells forming small lumina and spindle-shaped myoepithel ial cell with surrounding mucoid stroma. Components of pleomorphic adenoma were intermingled with mature adipose tissue which was more concentrated in the central portion of the adenoma. Some compressed epithelial cords in th e adipose tissue formed a septa-like pattern. The differential diagnosis to other lipomatous tumours (lipoadenoma, lipoma) and to nontumourous interst itial lipomatosis as well as the possible pathogenesis as metaplastic chang e or epithelial-mesenchymal transdifferentiation are discussed.