Primary Extraskeletal Osteosarcoma of Sigmoid Mesocolon: A Case Report and a Review of the Literature

Abstract Background: Extraskeletal osteosarcoma (ESOS) is a very rare mesenchymal malignancy, characterized by the production of osteoid, bone or chondroid material and typically located in the soft tissue without attachment to skeletal bones and periosteum. One of the things that ESOS originated from mesentery is much rarer. Case presentation: A 75-year female with a more than 4-months history of pain in the left lower abdomen. Abdominal computerized tomography and magnetic resonance imaging revealed a large, irregular and solid-cystic mass, which largest diameter was 11.5cm. The tumor was radically removed during open operation. The tumor was composed of abundant osteoid and polyhedral-shaped tumor cells with high atypia and high mitotic activity microscopically. The final pathological diagnosis was osteoblastic osteosarcoma, arising from the sigmoid mesocolon with negative margins. The patient was followed up 5 months after surgery and found no signs of systemic metastasis Conclusion: Given the rarity of cases of mesenteric ESOS, diagnosis mainly depended on pathology findings or should be taken into consideration when the mesenteric mass was found. Its most effective treatment had not been determined, with surgical excision was generally accepted. Negative surgical margin may be an important factor affecting the prognosis.