60 Wronski M et al. / Mesenteric fibromatosis FIGURE 1. The sonographic appearance of an intra-abdominal desmoid with involvement of the small bowel: a well-defined grossly homogenous hypoechoic mass circumferentially encroaching the intestinal wall; the hyperechoic central part of the tumour corresponds to intraluminal air that results in posterior acoustic shadowing (arrows). FIGURE 2. CT scan shows the desmoid tumour of the mesentery infiltrating the small bowel: a well-defined hypodense and homogenous mass dif- fusely attached to the bowel wall. raphy (CT) revealed a 8.2 x 7.2 x 7.4 cm mass in- filtrating the small bowel. The tumour attenuation was of 33 Hounsfield units and it enhanced poorly and homogenously with an intravenous contrast (Figure 2). The above preoperative imaging studies suggested a GIST involving the small bowel. The patient underwent an elective laparotomy. Intraoperatively, there was an approximately 10 cm well-circumscribed mass in the mesentery that in- Radiol Oncol 2011; 45(1): 59-63. filtrated the wall of the small bowel and narrowed its lumen (Figure 3). On inspection, there were also 2-3 small tubercules attached to the serosa of the adjacent bowel that were included within the re- section margins. Several similar lesions were found along the distal part of the small bowel and one of them was excised for the pathological evaluation. This gross appearance suggested a gastrointestinal stromal tumour with the peritoneal dissemina- tion. The resection of a 25 cm segment of the small bowel was performed. The postoperative course was uneventful and the patient was discharged in a good health condition. A follow-up US revealed no desmoid recurrence a year after the operation. The primary pathological diagnosis in this par- ticular case was a CD117-negative gastrointestinal stromal tumour. The small serosal tubercules were found to be mesothelial cysts. The principal diag- nosis was changed, however, after a consultation at a referral oncological centre. The microscopic examination of the resected specimen identified a fibromatosis in the mesentery. Histologically, the desmoid tumour was composed of spindle cells with elongated coma-shaped nuclei and the immu- nohistochemistry was negative for both CD117 and for CD34. Beta-catenin overexpression was present on immunohistochemistry (Figure 4). No mitoses were found in 50 high power fields. Discussion Mesenteric fibromatosis is a type of fibroblastic proliferation affecting the mesentery that develops usually as a consequence of surgical trauma, but it may occur spontaneously. Patients with famil- ial adenomatous polyposis (FAP, Gardner’s syn- drome) are especially predisposed to the develop- ment of mesenteric fibromatosis.1 Desmoids devel- op in approximately 10% of FAP patients and most are intra-abdominal. Similarily, fibromatoses asso- ciated with FAP follow a more aggressive course and the recurrence after the resection is common.2 The pathogenesis of fibromatoses has been un- clear for many years. Currently, these tumours are regarded as a clonal proliferation of myofibrob- lasts that show APC (adenomatous polyposis coli) gene mutations. These mutations lead to the over expression of beta-catenin.1,3,4 The clinical behaviour and the natural course of mesenteric fibromatoses are unpredictable. Some desmoid tumours remain stable for years and several cases of the spontaneous tumour regres- sion without any treatment have been reported.5