What is your diagnostic?

45 year-old female patient with abdominal distension and epi-/mesogastric pain. Physical examination showed palpable abdominal mass, confirmed by ultrasound. Her past medical history was without any particularities. Lab data were in normal limits.

Unenhanced and enhanced CT (Fig. 1), followed by MRI of the upper abdomen without (T1 Fat Sat, T2 FS weighted images) in axial plane and with paramagnetic Gd based contrast i.v.injection in  T1 Fat Sat coronal plane (Fig. 2) were performed, highlighting a well delimited solid mass, with progressive enhancement, located into the root of the mesentery. Selective superior mesenteric angiography was also done to complete the imaging evaluation of this patient (Fig. 3).

Surgical intervention revealed a solid-elastic apparent non-encapsulated, well-circumscribed dark-red mass of the mesenteric root. Postoperative evolution was favorable without any complication.

Mesenteric fibromatosis (MF) is a group of benign fibroproliferative processes that are locally aggressive and have the capacity to infiltrate or recur [1]. The small bowel mesentery is the most common site of intraabdominal fibromatosis. Other mesenteric structures which can be the site of origin for intraabdominal fibromatosis are: the mesentery root, the omentum, transverse or sigmoid mesocolon, and ligamentum teres [2,3]. MF occurs in patients aged between 14–75 years old (mean: 41yo), and has no gender or race predilection [2]. 13% of patients with MF have familial adenomatous polyposis, specifically, the Gardner syndrome variant [4,5]. Patients may complain of abdominal pain or palpable abdominal mass or come in emergency because of complications: gastrointestinal bleeding, small bowel obstruction, or perforation [4]. CT and magnetic resonance imaging (MRI) are the preferred imaging modalities for preoperative assessment of mesenteric masses determining lesion size and extent, as well as the degree of invasion into local structures [4]. MF may be discovered incidentally at ultrasound as a well-defined hypoechoic homogeneous, inhomogeneous, cystic or infiltrative mesenteric mass patterns [6]. CT and MRI findings of MF are directly related to the histologic characteristics and vascularity. Lesions with a highly collagenous stroma have homogeneous, or discreetly heterogeneous soft-tissue attenuation on CT (Fig. 1). Those with myxoid stroma appear hypoattenuating [7-9]. Some MF may appear striated because of the alternating collagenous and myxoid areas. In our case, we have observed a progressive contrast enhancement patterns, predominantly in the central part of the tumour (Fig. 2c, d). In MRI, most lesions are low or intermediate signal intensity on T1-WI (Fig. 2a) and have heterogeneously signal intensity on T2-WI (Fig. 2b), with hypointensity predominance [4,8,9]. MRI enhancement pattern of MF is similar to the CT, in our case the intramesenteric mass involving the superior mesenteric artery and vein branches (Fig. 2c, d). Selective superior mesentery angiography is not currently indicated in the diagnosis of mesenteric tumours (Fig. 3a, b). At gross examination, MF is typically a non-encapsulated, well-circumscribed mass [7]. At microscopic analysis, MF is composed of fibroblasts in an uninflamed, abundant collagenous stroma [4,8,9]. 

On imaging, MF is difficult to differentiate from malignant neoplasms of the mesentery, such as lymphoma, metastatic disease, sarcoma, as well as inflammatory pseudotumor, or GISTs of the small bowel. Some authors recommend wide surgical excision, whereas others recommend less radical surgery or medical therapy with antioestrogens or cytotoxic chemotherapy [10-14]. Histology and immunohistochemistry offers the definitive diagnostic of MF.