Primary Small Intestinal Leiomyosarcoma Presenting With Small Bowel Perforation: A Case Report.

A ​small intestinal leiomyosarcoma (LMS) is a rare malignancy that accounts for a small proportion of small bowel tumors and is often difficult to diagnose early due to its variable symptoms. This case report describes a 75-year-old female patient, previously suspected to have a gastrointestinal stromal tumor (GIST), presenting to the ED with abdominal pain and elevated inflammatory markers. A CT scan was performed which revealed a perforated mass in the distal ileum with surrounding collection. Consequently, she underwent laparoscopic washout, bowel resection, and primary anastomosis. Postoperatively, she developed paralytic ileus, which resolved with conservative management, and she was eventually discharged postoperative day 14. Histological and immunohistochemical analysis confirmed the diagnosis of an LMS, showing smooth muscle actin positivity, strong caldesmon labeling, and focal desmin expression with negative c-kit and S-100. The diagnosis of LMSs can be difficult, often misdiagnosed as GISTs due to overlapping features. Imaging studies, including CT scans, are valuable but not definitive. This case highlights the necessity of recognizing primary small intestinal LMSs as a potential cause of bowel perforation. Due to the rarity of LMSs and their potential for misclassification, accurate diagnosis and multidisciplinary management are crucial. Given the high risk of recurrence and metastasis, particularly due to perforation, long-term follow-up is also recommended.