2020 Volume 59 Issue 6 Pages 291-298
Background : Pigmented perivascular epithelioid cell tumor (PEComa) with marked melanin pigment deposition is a very rare tumor, that has been reported to arise mainly in the kidney and liver. We report a case of PEComa showing marked melanin pigment deposition arising from the retroperitoneum.
Case : A female patient in her 40 s was detected, during a medical checkup, as having a liver tumor. However, MRI revealed a retroperitoneal tumor. EUS-FNA was performed for cytological and histological diagnosis, which revealed round and spindle-shaped tumor cells. The tumor cell nuclei had granular chromatin and prominent nucleoli ; in addition, numerous brown granules were seen in the cytoplasm of the tumor cells, which were considered as being melanin granules.
Paraganglioma, PEComa and metastatic melanoma were considered in the differential diagnosis. Histologically, the tumor cells containing prominent melanin granules proliferated in an alveolar pattern, within a stroma containing proliferating large or small capillaries. Cellular atypia was prominent, but there were no mitoses. Immunohistochemically, the tumor cells showed positive staining for HMB-45, and negative staining for α-smooth muscle actin and S-100 protein. MIB-1- positive cells comprised less than 1% of the total cell population. The tumor was diagnosed as a pigmented PEComa.
Conclusion : It is important to recognize the cytological features of PEComa. The possibility of PEComa should be borne in mind in the differential diagnosis of tumors containing melanin granules in the cytoplasm.
