We report a rare case of leiomyosarcoma derived from the mesosigmoid that was difficult to differentiate from ovarian tumor. A 50-year-old woman seen for a left lateral abdominal mass was admitted with a left ovarian tumor suspected after CT. The tumor was palpable as a hard, irregular mass 14 cm in diameter in the left lower abdominal quadrant. US showed a low echoic mass adjacent to the left ovary and an irregular 14 x 13 x 8 cm mass and ascites in the Douglas cavity. MRI showed low-intensity in T1-weighted images and low intensity in the margin and high intensity in T2-weighted images. The tumor, which was localized in the mesosigmoid, adhered to the left ovary and had invaded to sigmoid colon. We diagnosed it as sarcoma of the mesosigmoid and conducted sigmoidectomy with en bloc resection of the tumor and left ovary. Neither metastasis nor peritoneal dissemination was seen. The tumor was hard, solid, and yellowish with internal necrosis. Pathological findings showed dense fusiform cells with aberrant large-sized nuclei and frequent mitosis. Immunohistochemistry showed leiomyosarcoma because α-SMA and desmin were strongly positive but Ki67 and CD34 were negative. The patient's course remains uneventful 5 months after surgery, but will continue to require close follow-up.
- Gastrointestinal stromal tumor
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