Sporadic Desmoid-Type Fibromatosis of the Small Intestine Muscularis Propria: A Case Report.

Desmoid-type fibromatosis is a rare, locally aggressive tumor of fibroblastic origin that typically arises from the mesentery or abdominal wall. Sporadic desmoid-type fibromatosis originating from the small intestinal wall is extremely rare and presents unique diagnostic challenges due to its nonspecific imaging findings and lack of mucosal involvement. A 69-year-old man with a history of prostate cancer and right renal cell carcinoma underwent routine postoperative surveillance, during which a proximal jejunal mass was incidentally detected on contrast-enhanced computed tomography (CT). Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) revealed moderate FDG uptake (maximum standardized uptake value (SUVmax), 3.62), raising suspicion for gastrointestinal stromal tumor or metastatic disease. Double-balloon enteroscopy showed no mucosal or submucosal lesions. Surgical exploration revealed four masses, including one arising from the muscularis propria of the jejunum and three within the mesentery. The jejunum was resected over a length of 80 cm, and reconstruction was performed using functional end-to-end anastomosis after extensive duodenal mobilization. Histopathological examination confirmed desmoid-type fibromatosis. The patient recovered uneventfully. This case highlights the diagnostic difficulty and potential for multifocality in sporadic intra-abdominal desmoid-type fibromatosis. It underscores the importance of including desmoid-type fibromatosis in the differential diagnosis of mesenteric or submucosal tumors, especially in patients with a history of abdominal surgery. Surgical exploration and tailored reconstruction strategies are essential for achieving curative resection while preserving bowel length. Given the patient's history of prior abdominal surgeries, this case supports the hypothesis that surgical trauma may contribute to tumor development in sporadic desmoid-type fibromatosis.