Pelvic solitary fibrous tumor originally diagnosed as prostatic in origin.

A 71-year-old man was referred to our hospital because of intermittent urine stream and postmicturition dribbling. Magnetic resonance imaging (MRI) results suggested the mass to be a malignant mesenchymal tumor arising from the left lobe of the prostate, on the basis of the presence of a beak sign. Radical prostatectomy and partial rectal excision with subsequent colostomy were performed. Contrary to preoperative MRI, no prostate involvement was found on histologic examination. Histopathologic and immunohistochemical findings showed typical characteristics of solitary fibrous tumors. The patient's postoperative course was uneventful. He showed no signs of recurrence and metastasis at 2-year follow-up.