一名 20 多岁的男性因左前臂前外侧出现无痛、缓慢生长的硬肿块就诊。肿胀已持续一年，尺寸为10×12厘米。临床上考虑与四肢软组织肉瘤、脂肪瘤、神经纤维瘤、皮样囊肿、包虫囊肿等进行鉴别诊断。 MRI提示原发性肌内包虫囊肿。然而，细针抽吸结果尚无定论，且血清中棘球蚴抗原免疫球蛋白G抗体的ELISA结果呈阴性。计划对病变进行广泛局部完整手术切除。术中，在肌内平面内发现边界清晰、紧张的囊性肿胀，周围有致密粘连。囊肿壁的组织病理学检查显示囊尾蚴病。病人康复顺利。该病例强调，孤立性肌内囊尾蚴病虽然罕见，但应纳入孤立性软组织肿块的鉴别诊断，特别是在流行地区。© BMJ Publishing Group Limited 2024。不得商业重复使用。请参阅权利和权限。英国医学杂志出版。

A man in his 20s presented with a painless, slow-growing firm swelling in the anterolateral aspect of his left forearm. The swelling had been present for 1 year and measured 10×12 cm. Clinically, a differential diagnosis of soft tissue sarcoma, lipoma, neurofibroma, dermoid cyst and hydatid cyst of the extremity was considered. MRI suggested a primary intramuscular hydatid cyst. However, fine-needle aspiration was inconclusive, and ELISA for immunoglobulin G antibodies to echinococcal antigen in serum was negative. A wide-local complete surgical excision of the lesion was planned. Intraoperatively, a well-defined, tense cystic swelling with surrounding dense adhesions was found within the intramuscular plane. Histopathological examination of the cyst wall revealed cysticercosis. The patient recovered uneventfully. This case highlights that solitary intramuscular cysticercosis, although rare, should be included in the differential diagnosis of an isolated soft tissue mass, particularly in endemic areas.© BMJ Publishing Group Limited 2024. No commercial re-use. See rights and permissions. Published by BMJ.