Aggressive Fibromatosis of the Left Mesocolon Mimicking a Gastrointestinal Stromal Tumor: A Case Report.

Mesenteric fibromatosis (MF) is a proliferative fibroblastic lesion of the intestinal mesentery. It constitutes 8% of all desmoid tumors, representing 0.03% of all neoplasms. It is benign histologically, although it could infiltrate locally and recur following excision; however, it is free from the potential to metastasize. It is spontaneous or associated with familial adenomatous polyposis (FAP]) mutation as a part of Gardner's syndrome. This case report discusses the radiological, intraoperative, and histopathological findings from a 45-year-old male patient who presented with abdominal pain and a palpable mass in the left hemiabdomen. The pain was dull and aching, extending to the back and unrelated to any other gastrointestinal symptoms. There was no history of severe weight reduction. Furthermore, he is not a smoker. There were no comorbidities, severe medical diseases, or prior surgical procedures. Computerized tomography revealed a well-defined, lobulated, heterogeneously enhancing altered signal intensity mass at the mesocolon. Ultrasonography of the abdomen showed an intra-abdominal mass. Macroscopic mass characteristics include a well-defined mass measuring 22 × 14 × 11 cm connected to a small intestine segment measuring 21 × 2 × 2 cm. Histopathological and immunohistochemical examinations of the resected tumor, including positive nuclear immunostaining for beta-catenin, confirmed a postoperative diagnosis of desmoid-type fibromatosis. Based on its clinical presentation and computed tomography results, this case demonstrated how desmoid-type fibromatosis of the colon might mimic gastrointestinal stromal tumors (GISTs). Due to the varied therapies and follow-up methods used for these lesions, the differential diagnosis between desmoid-type fibromatosis and GIST is clinically significant.