Pigmented Caruncular Apocrine Hidrocystoma With Oncocytic Features.

An unprecedented pigmented caruncular apocrine hidrocystoma with the additional feature of an oncocytic transformation of the cyst's lining cells is reported. Over a year, a 79-year-old woman developed a centrally pigmented lesion of her right caruncle with translucent borders. Because of concern about a melanoma, a carunculectomy with adjunctive cryotherapy and placement of an amniotic membrane graft were performed, and the excised specimen was evaluated microscopically. A large cyst dominated the caruncle and was lined by an inner layer of columnar eosinophilic and granular cells with an outer, interrupted layer of flattened myoepithelial cells. Phosphotungstic acid hematoxylin staining disclosed myriad cytoplasmic, dot-like mitochondria signifying an oncocytic change. Immunohistochemistry revealed gross cystic fluid disease protein-15 and cytokeratin 7-positivity indicative of apocrine differentiation. Oncocytic change is characteristically encountered in lacrimal ductal cysts and tumors.