Sclerosing polycystic adenosis of the parotid gland: report of one case diagnosed by fine-needle cytology with in situ malignant transformation.

Sclerosing polycystic adenosis (SPA) is a rare pathological condition affecting the salivary glands, first described by Smith etal. in 1996. Even though this lesion is being increasingly diagnosed, less than 50 cases have been published in the world literature to date. In line with numerous other pathological analogies between breast and salivary gland lesions, SPA shares with fibrocystic disease of the breast many histopathological features, i.e., fibrosis, oncocytic (apocrine) changes, hyperplasia of ductal and acinar epithelium, cystic dilation of ducts, and, often, atypical epithelial changes. Most of the described cases have followed a benign clinical course, despite the frequent possibility of atypical hyperplasia in more than 50% of the cases and of the more than occasional in situ malignant transformation. In this article, we introduce a new case occurring in the parotid gland of a 57-year-old male showing atypical epithelial hyperplasia and low-grade in situ mucoepidermoid carcinoma. Fine-needle cytology (FNC) was performed on the lesion and, when a diagnosis of SPA was prospected, the variegated cytological features of the obtained sample posed several differential diagnostic problems. The spectrum of pathological lesions entering differential diagnosis comprised sebaceous adenoma, Warthin's tumors with presence of sebaceous remnants, and low-grade mucoepidermoid carcinoma. Histopathological examination disclosed SCA with intraductal neoplastic transformation resembling noninvasive low-grade mucoepidermoid carcinoma. The cytological diagnosis of SPA should be entertained whenever a polymorphous picture is found on FNC samples comprising oncocytic/apocrine changes, sebaceous cells, cystic background, and epithelial hyperplasia with low-grade cytological atypias.