Male urethral diverticulum: the double density sign.

An anatomic defect of the urethra is occasionally the cause of voiding dysfunction in the young male patient. A urethral diverticulum can often be overlooked if retrograde urethrography is not performed properly. Two cases are presented along with a discussion of the technique for dynamic retrograde urethrography. The description of a new radiologic sign indicative of a posterior bulbar urethral diverticulum, is presented.