Abstract
Aggressive fibromatosis is a rare type of intra-abdominal desmoid tumour that usually involves the small bowel mesentery. It is a locally-invasive lesion, with a high rate of recurrence, but without metastatic potential. Aggressive fibromatosis is seen more often in young female patients. This case report presents the radiological, intraoperative and histopathological findings from a 37-year-old female patient that presented with epigastric pain and a palpable mass in the right hemiabdomen. Histological and immunohistochemical examinations of the resected tumour, including positive staining for beta-catenin, confirmed a postoperative diagnosis of desmoid type fibromatosis. This specific case showed that desmoid type fibromatosis of the colon can mimic gastrointestinal stromal tumours (GIST) based on its clinical presentation, computed tomography and magnetic resonance imaging findings. Differential diagnosis between desmoid type fibromatosis and GIST is clinically very important due to the different treatments and follow-up protocols that are implemented for these lesions.