[Solitary Fibrous Tumor in the Pelvic Space : A Case Report].

A 46-year-old man was found to have a mass in the pelvic cavity on computed tomography (CT) carried out for an examination for lower abdominal pain. Abdominal magnetic resonance imaging showed a mass which appeared to have hyposignals on both T1- and T2-weighted images. A positron emission tomography CT showed that the mass had a low maximum standardized uptake value (＝1.4). Biopsy of the mass showed tumoral cells demonstrating a 'patternless pattern' characterized by a haphazard, storiform arrangement of short spindle or ovoid cells. Immunohistochemistry disclosed CD34 positivity and desmin and alfa-smooth muscle actin (SMA) negativity which supported the diagnosis of solitary fibrous tumor. Tumorectomy was performed. Grossly, the tumor was a large encapsulated mass with well limited margins weighing 67.7 g. Histology revealed a mass with no necrotic or hemorrhagic degeneration. On immunohistochemistry, the tumor cells were strongly positive for CD34 and they were negative for desmin and alfa-SMA. At six months of follow up, the patient was well and he had no signs of recurrence.