Perivascular Epithelioid Cell Tumor Arising in the Sacrum: A Case Report

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Perivascular epithelioid cell tumor (PEComa) is a rare and recently described neoplasm composed mainly of epithelioid cells with a characteristic perivascular pattern of arrangement. 1 The diagnosis can be confirmed by immunohistochemical (IHC) staining as tumor cells express melanocytic and myogenic markers. 2 These tumors can occur in a wide variety of organs including the kidney, liver, lung, uterus, and pancreas. 3 We report the case of a PEComa arising from the sacral bone, which is an exceedingly rare site for a PEComa. Although there have been several reports of PEComas originating from bone, to our knowledge this is the first case report of a PEComa arising from the sacral bone. A 45-year-old man without relevant medical history presented with left buttock and leg pain 1.5 months in duration. Sacral magnetic resonance imaging revealed a 5.5×4.7-cm lobulated osteolytic expansile mass on the left side of the sacrum (Fig. 1A). The tumor was invading the lumbo-sacral spinal canal medially via neural foramens S1-3 and laterally via the left sac-roiliac joint. Positron emission tomography showed increased fluorodeoxyglucose uptake, suggesting malignancy. Due to the radiologic characteristics, a germ cell tumor or nerve sheath tumor was considered. An excisional surgery was performed, and intraoperatively the tumor was found to be solid and multilob-ulated, and was covered with a thin vascularized capsule. It was easily separated from the sacral nerve roots and sacral bone, thus allowing for near total removal. The tumor bed was then treated with postoperative radiation therapy (64.8 Gy) without complication. The tumor was relatively poorly demarcated from normal tissue and showed rich networks of arborizing sinusoidal capillar-ies. It was composed exclusively of polygonal and epithelioid cells with abundant clear to eosinophilic cytoplasm, most of which was arranged in sheets or a vague nesting pattern (Fig. 1B). Occasional perivascular arrangements were also noted (Fig. 1C). Infiltration into adjacent bone tissue was found (Fig. 1D), but no necrosis or mitosis was observed. The initial differential diagnosis included ependymoma, hemangioblastoma, paragan-glioma, and epithelioid neurogenic tumor. Many IHC stains were performed, but none of the tumor cells showed immuno-reactivity to antibodies except smooth muscle actin (SMA) (Fig. 2A). Several additional IHC stains were done and human mela-noma black …