Malignant Perivascular Epithelioid Cell Tumor Originating from the Transverse Mesocolon

Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal neoplasms with melanocytic and smooth muscle differentiation. Primary mesenteric PEComas are exceptionally uncommon and usually cannot be diagnosed from imaging alone. We report a case of malignant PEComa arising from the transverse mesocolon.

A 34-year-old woman was referred to our department after abdominal ultrasonography showed a large intra-abdominal mass. Contrast-enhanced CT revealed a 15-cm heterogeneous, hypervascular mesenteric tumor with internal necrosis and feeding vessels from the superior mesenteric artery. MRI showed no continuity with the uterus or ovaries. Because percutaneous biopsy was considered to carry a substantial risk of bleeding and dissemination, the tumor was resected for diagnosis and treatment. Laparotomy demonstrated a transverse-mesocolic tumor directly invading the transverse colon; transverse colectomy with en bloc tumor resection was performed. Histopathological evaluation showed pleomorphic epithelioid cells, marked nuclear atypia, coagulative necrosis, vascular invasion, and frequent mitoses. The tumor was positive for HMB-45, Melan-A, and smooth muscle actin and negative for TFE3, supporting malignant PEComa. The postoperative course was uneventful, and the patient remained free of recurrence 4 months after surgery.

Malignant PEComa of the transverse mesocolon is extremely rare. This tumor should be considered among large, hypervascular mesenteric tumors, although imaging is not specific. Complete resection with negative margins is the principal treatment for localized disease. High-risk pathological features justify prolonged cross-sectional imaging surveillance and multidisciplinary, molecularly informed management if recurrence develops.