Perivascular epithelioid cell tumor (PEComa) of the cystic duct

Perivascular epithelioid cell tumors, also known as PEComas, are rare mesenchymal tumors composed mainly of epithelioid cells found in perivascular tissue. PEComas occur most frequently in the kidney, uterus, the gastrointestinal tract, liver, and retroperitoneum; those originating in the biliary tree are extremely rare. We report a case of benign PEComa of the cystic duct with positive TFE3 staining on immunohistochemistry. A 66-year-old woman was referred for a 20 mm mass adjacent to the common bile duct discovered incidentally on abdominal ultrasound. Laboratory data including tumor markers were unremarkable. The tumor appeared to arise from the cystic duct, showed early enhancement, and compressed the common bile duct on imaging studies. Endoscopic ultrasound-guided fine-needle aspiration revealed round- and spindle-shaped atypical cells with eosinophilic cytoplasm and brown deposits suggestive of melanin granules. Histological examination of the resected specimen revealed a tumor consisting of epithelioid cells forming an alveolar structure, with melanin pigmentation. Immunohistochemistry was positive for HMB-45 and TFE3, consistent with benign pigmented PEComa of the cystic duct. Melanotic, myogenic, and TFE3 staining are helpful when diagnosing PEComas arising in unusual locations.