Extraskeletal osteosarcoma (ESOS) is a rare mesenchymal malignancy, which produces osteoid, bone, or chondroid material and is located in the soft tissue without attachment to skeletal bones and periosteum. One of the things that ESOS originated from mesentery is much rarer. A 75-year female had a history of pain in the left lower abdomen for more than 4 months. Abdominal computerized tomography (CT) and magnetic resonance imaging revealed a large, irregular, and solid-cystic mass (largest diameter was 11.5 cm). The tumor was radically removed during an open operation. It 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. A 9-month follow-up by CT exhibited signs of peritoneal metastasis. 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 being generally accepted. Ensuring negative surgical margins may be an important factor affecting prognosis.

中文翻译：

---

乙状结肠系膜原发性骨外骨肉瘤1例报告并文献复习

骨骼外骨肉瘤 (ESOS) 是一种罕见的间充质恶性肿瘤，产生类骨质、骨或软骨样物质，位于软组织中，不附着于骨骼和骨膜。ESOS起源于肠系膜的其中一种情况更为罕见。一名 75 岁女性，有左下腹疼痛 4 个月以上。腹部计算机断层扫描 (CT) 和磁共振成像显示一个大的、不规则的、实性囊性肿块（最大直径为 11.5 厘米）。肿瘤在开放手术中被彻底切除。它由丰富的类骨质和多面体形肿瘤细胞组成，显微镜下具有高异型性和高有丝分裂活性。最终病理诊断为成骨细胞性骨肉瘤，起源于边缘阴性的乙状结肠系膜。9 个月的 CT 随访显示有腹膜转移的迹象。鉴于肠系膜ESOS病例罕见，诊断主要依靠病理结果或在发现肠系膜肿块时考虑。其最有效的治疗方法尚未确定，手术切除已被普遍接受。确保阴性手术切缘可能是影响预后的重要因素。