Mesenteric desmoid tumor with diagnostic challenge mimicking a malignant small intestinal tumor: a case report.

Introduction and importance: Desmoid tumors are histologically benign fibroblastic neoplasms with locally aggressive behavior and no metastatic potential. Intra-abdominal desmoid tumors often lack specific imaging features, and preoperative tissue diagnosis may be difficult, complicating treatment decision-making. Case presentation: A 66-year-old man presented with a painless abdominal mass sensation. Contrast-enhanced computed tomography revealed a well-circumscribed intra-abdominal mass measuring approximately 12 × 10 cm, adjacent to the small intestine, with heterogeneous enhancement and internal low-attenuation areas, raising suspicion of a malignant small intestinal tumor, particularly a gastrointestinal stromal tumor. Surgical resection was performed without a preoperative biopsy due to persistent symptoms and diagnostic uncertainty. The tumor was located within the small bowel mesentery and was resected en bloc with the adjacent small intestine. Histopathological examination confirmed a mesenteric desmoid tumor. Familial adenomatous polyposis was absent, and the tumor was considered sporadic. Clinical discussion: Mesenteric desmoid tumors may cause tumor-related symptoms without bowel obstruction or overt invasion, and their nonspecific imaging characteristics may lead to diagnostic challenges. In such situations, diagnostic uncertainty can directly influence surgical decision-making and treatment strategy. Conclusion: This case highlights the importance of considering desmoid tumors in the differential diagnosis of intra-abdominal masses and demonstrates how diagnostic uncertainty can influence the treatment strategy.