[Solitary fibrous tumor confined to the small bowel (ileum) mesentery].

In 1942 Stout and Murray first described hemangiopericytoma (HPC) as a vascular tumor composed of Zimmerman’s pericytes. In 1980 Wagner made the first histologic description of a solitary fibrous tumor (SFT) in the pleura, and in 1931 Klemperer and Rabin recognized it as a distinctive entity. Ultra-structurally, both the HPC and the SFT show variable characteristics of pericytic, fibroblast, and/or myofibroblast differentiation. Thanks to the exponential increase in the reports on SFT, the conclusion was reached that it did not only present in serous membranes. Currently, due to the superposition of the main histologic characteristics and the lack of specific criteria for determining whether a lesion is SFT or HPC, pathologists have decided to abandon the term HPC in favor of SFT. Localized SFT in the small bowel mesentery is an extremely rare tumor, with only 3 cases reported on in PubMed. The aim of presenting this case was to provide current knowledge about SFT classification and to report the 4th case of SFT in the small bowel mesentery. An 82-year-old man was brought to the emergency room of the Hospital Nacional Guillermo Almenara Irigoyen (HNGAI) by his relatives for medical attention due to 10 days of colicky abdominal pain that increased in intensity as the days went by; he also presented with nausea, vomiting, fever of 40 ◦C, and sensory disorder. During a thorough anamnesis, the patient stated he had experienced similar symptoms 4 months earlier, associated with dyspepsia and involuntary weight loss of 3 kg at that time. Physical examination showed mild paleness, moderate pain upon palpation of the right hypochondrium, mesogastrium, and hypogastrium. In addition, a 15 x 15 cm painful mass was palpated in the hypogastrium, while the rest of the physical examination was unremarkable. A bowel transit time test indicated delayed transit, discreet dilation of the jejunoileal segments, and signs of flocculation with no intramural images. A contrast-enhanced abdominal tomography scan revealed an expansive lesion with hypervascularity that was in contact with the distal ileum, associated with an alteration in the surrounding adipose tissues, and signs of hemoperitoneum predominating in the pelvic cavity recesses. The efferent venous drainage that was dependent on the mesenteric veins, whose diameters were enlarged, was striking, and the diagnostic imaging service recommended considering hemangioma, hemangiosarcoma, carcinoid tumor, hemangiopericytoma, and stromal tumor in the differential diagnoses. As a result of the discussion of the clinical cases of the coloproctology service of the HNGAI, an exploratory laparotomy + resection of the tumor of the distal ileum