Solitary fibrous tumor of the pelvis: an uncommon soft-tissue tumor. A case report.

A rare case of Solitary fibrous tumor (SFT) of the pelvis is reported. A 76-years-old man presented with a low abdominal pain, acute urine retention and constipation. Imaging studies (US, CT MR) showed an 17 x 10 x 9 ovoid mass in the pelvis, dislocating bladder and rectum. Finally, trans-rectal needle biopsy suggested the diagnosis of SFT. En bloc excision of tumor and rectum (because of strong adhesions) was performed. Histological examination showed spindle and fibroblastic-like cells dispersed in collagenous areas with positive stains for CD34, bcl-2, CD99 and it confirmed diagnosis of SFT. No postoperative complications occurred, only vesico-sphincter dyssynergia was found by urodynamics. After 5 years, patient is disease-free. SFT is, usually, benign tumor with slow growth and excellent prognosis. Complete surgical resection is the only curative treatment. However, 10-15% of SFT are malignant and histological findings cannot always predict clinical behaviour. For this reason, careful and long term follow-up is necessary after surgery.