Gastrointestinal stromal tumor versus intra-abdominal fibromatosis of the bowel wall : A clinically important differential diagnosis

Intra-abdominal fibromatosis (IAF) is an uncommon benign neoplasm that usually occurs in the mesentery or retroperitoneum and may, on occasion, mimic a gastrointestinal stromal tumor (GIST). Differentiating between these two entities is important clinically because IAF is a benign tumor whereas GISTs frequently have malignant potential. In this study, the authors identified 13 cases of IAF with prominent involvement of the bowel wall as well as 35 GISTs of the small intestine, colon, or mesentery and analyzed their clinical, gross, histologic, immunophenotypic, and ultrastructural characteristics to identify important distinguishing features. Patients with IAF were younger (mean, 34 yrs) than patients with GIST (mean, 54 yrs). Both types of tumors tended to be large, but GISTs were soft and lobulated with hemorrhage, necrosis, or cystification whereas IAFs were firm, tan, and homogeneous. Histologic features characteristic of GIST included the presence of spindle or epithelioid cells with variable architecture, mitotic activity (range,