An Unusual Presentation of Leiomyosarcoma Mimicking Parasitic Fibroids: A Diagnostic Dilemma

Uterine leiomyosarcoma (uLMS) is a rare and aggressive mesenchymal malignancy associated with a high risk of recurrence and metastatic spread. Although recurrent disease commonly presents with infiltrative or bulky pelvic masses, atypical patterns of dissemination may create diagnostic challenges. We present the case of a 49-year-old woman with a history of FIGO stage IB uterine leiomyosarcoma who underwent total abdominal hysterectomy with bilateral salpingo-oophorectomy in 2023 and subsequently received treatment for recurrent metastatic disease. She presented with acute lower abdominal pain, persistent vomiting, and progressive obstipation. Computed tomography demonstrated a large heterogeneous pelvic mass measuring approximately 14 cm, together with features of a closed-loop small bowel obstruction and mesenteric vessel twisting suggestive of volvulus. Following clinical deterioration despite conservative management, emergency exploratory laparotomy was performed, revealing a 360-degree small bowel volvulus around the superior mesenteric artery pedicle, which was successfully reduced. A large fixed pelvic mass involving adjacent bowel and mesentery was identified, along with numerous smooth, firm, pedunculated nodules distributed throughout the mesentery, bowel serosa, and parietal peritoneum. These nodules had a gross appearance resembling benign parasitic leiomyomas or disseminated peritoneal leiomyomatosis rather than metastatic sarcoma. Segmental small bowel resection with double-barrelled ileostomy was undertaken due to bowel compromise and extensive serosal injury. Histopathological examination of the resected nodules demonstrated atypical spindle cells arranged in intersecting fascicles with moderate nuclear atypia and a mitotic rate of 5-10 mitoses per 10 high-power fields. Immunohistochemical analysis showed diffuse positivity for smooth muscle actin, desmin, and h-caldesmon, with abnormal mutant-pattern p53 expression, confirming multifocal metastatic uterine leiomyosarcoma. This case demonstrates an unusual pattern of metastatic uLMS presenting with a benign-appearing peritoneal distribution and complicated by acute small bowel volvulus and obstruction. The findings highlight the importance of histopathological and immunohistochemical assessment in distinguishing metastatic smooth muscle malignancy from benign-appearing lesions and emphasise the need for multidisciplinary management in complex recurrent disease.