The urethra is the tube that runs from the bladder through the prostate and penis. A urethrogram is usually carried out to show the cause of poor urinary flow thought to be caused by narrowing (a stricture) of the urethra. The most common cause for narrowing of the urethra in men is benign (non-cancerous) enlargement of the prostate gland. A urethrogram is most often used to diagnose causes of narrowing of the urethra that are not caused by benign enlargement of the prostate gland.