Localized intra-abdominal fibromatosis of the small bowel mimicking a gastrointestinal stromal tumor: a case report.

Intra-abdominal fibromatosis (IAF) is a benign mesenchymal lesion that can occur throughout the gastrointestinal tract. Although rare, it is the most common primary tumor of the mesentery and can develop at any age. We describe a rare case of primary IAF involving the mesentery and small bowel which clinically, macroscopically and histologically mimicked malignant gastrointestinal stromal tumor (GIST). This report highlights the fact that benign IAF can be misdiagnosed as a malignant GIST localized in the mesentery or arising from the intestinal wall. Their diagnostic discrimination is essential because of their very different biological behaviors and the fact that the introduction of effective therapies involving tyrosine kinase inhibitor STI571 (imatinib mesylate) has greatly changed the clinical approach to intra-abdominal stromal spindle cell tumors.