S3929 Primary Mesenteric Fibromatosis With Multi-Organ Compression: A Case of Surgical Complexity

Introduction: Mesenteric fibromatosis (MF) is a benign form of desmoid tumors that originates in the abdominal mesentery. Although benign, MF often demonstrates locally aggressive progression. It is characterized by the proliferation of well-differentiated fibroblasts and myofibroblasts that, as they grow, may compress surrounding organs, leading to intestinal obstruction, ischemia, and perforation. Accounting for 2 to 4 new cases per million people per year and with an incidence of only 0.03%, MF is considered a rare tumor. In the abdomen, apart from developing within the mesentery, it may also be seen in the mesocolon and the retroperitoneum. We report a case with mild, nonspecific symptoms of MF that required a high index of suspicion to perform the appropriate workup and extraction. Case Description/Methods: A 24-year-old woman with no significant medical history arrived at the Gastroenterology clinic after experiencing nausea, constipation, and abdominal pain for 6 months. Magnetic resonance imaging and ultrasound of the abdomen revealed a large 3.3 × 3.7 cm mass near the splenic hilum with evidence of colonic and pancreatic tail compression and no invasion. Subsequent colonoscopy revealed an extracolonic mass with significant compression of the colon. Endoscopic ultrasound with biopsy was remarkable for fibroblastic/myofibroblastic cell proliferation of unknown significance, characteristic of primary MF. Exploratory laparotomy revealed a densely fibrous mass adhered to the splenic hilum, splenic flexure of the colon, and pancreatic tail, which required splenectomy, distal pancreatectomy, and partial colectomy. She tolerated the procedure without complications, and no recurrence occurred during screening. Discussion: MF commonly occurs in women of reproductive age, either associated with another condition, such as Gardner’s syndrome or as a spontaneous isolated mesenteric fibromatosis (SIMF). It has been previously associated with past abdominal surgeries or estrogen exposure. Despite its benign nature, it can grow aggressively and cause mass effect complications on local organs. Abdominal imaging with the ultrasound, computed tomography scan, or magnetic resonance imaging can detect extraintestinal lesions, but a colonoscopy must also be performed due to the possible presence of intracolonic tumors and its feasibility of obtaining a biopsy for diagnosis. Surgical resection is the first choice for management. Yearly follow-up is recommended in all patients due to its recurrence of 23% to 50%.