Received December 8, 2008, from the Department of Radiology, Derriford Hospital, Plymouth, England. Revision requested December 29, 2008. Revised manuscript accepted for publication January 13, 2009. Address correspondence to Nanda Venkatanarasimha, MBBS, MRCP, FRCR, Department of Radiology, Derriford Hospital, Derriford Road, Plymouth PL6 8DH, England. E-mail: nandashettykv@yahoo.com Abbreviations MRI, magnetic resonance imaging 45-year-old male patient underwent transrectal sonography to assess a 3-month history of perineal pain, dysuria, painful ejaculation, and postvoid dribble. The pain was worse after alcohol and on sitting. The patient had no relevant medical or surgical history. Urinalysis and blood test results for inflammatory markers were negative. Transrectal sonography showed a multiseptated cystic mass at the apex of the prostate (Figure 1). Color Doppler imaging showed no internal flow (Figure 2). A paraurethral diverticulum, congenital mullerian duct abnormalities, a prostatic retention cyst, and a chronic prostatic abscess were considered in the differential diagnosis. Follow-up transrectal sonography (Figure 3) performed 4 months later showed a slight increase in size and a cystic component to the right of the prostatic urethra. Magnetic resonance imaging (MRI) of the prostate (Figures 4 and 5) performed for further evaluation showed a multiseptated cystic mass anterior to the prostatic apex and encasing the posterior urethra. Appearances on MRI were consistent with a paraurethral diverticulum, the other differential diagnoses being considered less likely. Cystoscopy and urethrography (Figure 6) confirmed a urethral diverticulum with a large neck arising from the left posterolateral wall of the urethra at the level of the verumontanum. Histologic assessment showed nonspecific inflammatory changes and no evidence of neoplasia. A posterior urethral diverticulum is usually acquired1 and is rare in men. The classic clinical triad of urethral diverticula, although infrequently observed, includes dysuria, postvoid dribbling, and dyspareunia.2 The causes of urethral diverticula include congenital origins, recurrent infections, and instrumentation or surgery; when acquired, they are thought to result from inflammation and trauma of the periurethral glands and ducts, leading to local glandular dilatation and subsequent rupture into the urethra.3 Because our patient had no evi-