Mesenteric fibromatosis Demographics 25-35 year, F>M Clinical manifestations Asymptomatic, unless large, infiltrating bowel or compressing the ureters and vasculature; Common: abdominal pain Rare: GI bleeding, perforation Location Small bowel mesentery US CT MRI Gross appearance Microscopic view Immunostaining profile GI, gastrointestinal Smooth well-defined margins, homogenous or heterogenous tumour of variable echogenicity Well-defined homogenous mass, isodense or hy- perdense relative to muscle, 1/3 show infiltrative margins, cystic degeneration is rare Tumour of low signal intensity relative to muscle on T1-weighted images and variable signal in- tensity on T2-weighted images Homogenously distributed spindle cells without atypia, abundant collagen, thick-walled arteries and dilated thin-walled veins, mild cellularity, infiltrative pattern of growth β-catenin (+) CD117 (+) in up to 75% CD34 (-) vimentin (+) smooth muscle actin (+) in 75% desmin (+) in 50% 62 Wronski M et al. / Mesenteric fibromatosis TABLE 1. The clinicopathological features useful in differentiating mesenteric fibromatosis from gastrointestinal stromal tumours (GIST) GIST 50-60 year, F=M Common: abdominal pain, GI bleeding Rare: GI perforation, obstruction Anywhere along the GI tract; most common in the stomach and small bowel Extraluminal hypoechoic mass, small tumours are homogenous, large tumours are heterogenous with multiple anechoic patchy spaces or large central area of low echogenicity Well-defined heterogenous mass with peripheral solid rim enhanc- ing with contrast, central fluid attenuation (necrosis, haemorrhage, cystic degeneration); small tumours show homogenous enhance- ment Tumour of low signal intensity relative to muscle on T1-weighted im- ages and high signal intensity on T2-weighted images Spindle or epithelioid cells forming fascicles and palisades often with atypia and atypical mitoses, moderate to high cellularity, necrosis often present, expanding pattern of growth β-catenin (-) CD117 (+) in 90% CD34 (+) in 42% vimentin (+) smooth muscle actin (+) in 63% desmin (+) in 8% Hard and firm mass, cut with gritty sensation, white-greyish and glistening on cut section Soft and fleshy tumours that often show areas of necrosis, haemor- rhage and cystic degeneration on cut surface desmoid tumours encroaching the bowel wall fibromatosis is based on the microscopic examina- present a diagnostic challenge and might be easily tion and immunostaining. It is noteworthy that a confused with primary intestinal tumours, espe- CD117 antigen, expressed commonly in GISTs, cially gastrointestinal stromal tumours. Difficulties can be positive in up to 75% cases of mesenteric in differentiating these two tumours of distinct fibromatosis.11-13 Moreover, both MF and GISTs ex- pathogenesis, natural course and prognosis are press vimentin and stain variably for smooth mus- still not uncommon.12-14 cle actin and desmin. In contrast to GISTs, MF does Desmoid tumours are firm masses. On cross sec- not express CD34 and S100 protein. Recently, the tion these tumours are grayish and grossly homog- expression of beta-catenin was revealed in fibrom- enous. In comparison, GISTs are usually soft and atoses that might prove helpful in the differential fleshy. On cut surface, these tumours commonly diagnosis in doubtful cases.1,15,16 have areas of necrosis and haemorrhage. In con- Radiographically, mesenteric fibromatosis trast to MF, the gross appearance of GISTs is highly may present as a mass-like or infiltrative lesion.17 dependant on their size, with large tumours being Infiltrative desmoid tumours image as an ill-de- morphologically more heterogeneous. It follows fined whorled thickening of the mesentery and that a large tumour that is firm and homogenous are usually easily recognized. Mass-like desmoids on cross section without obvious haemorrhagic are more challenging. These desmoids appear as and necrotic areas is highly suggestive of intra-ab- well-defined tumours and are often confused with dominal fibromatosis. Sometimes, differentiating other primary neoplasms, especially gastrointesti- these two distinct tumours is difficult because of a nal stromal tumours. Nevertheless, the distinction possible clinical, macroscopic and even histological between these two tumours is important because overlap. Nevertheless, the diagnosis of mesenteric of vital prognostic and therapeutic implications. In Radiol Oncol 2011; 45(1): 59-63.