Enlarged prostate: false-colour intravenous urogram (IVU) showing an enlarged prostate, which appears as the pale gold shadow on the dark red, contrast-filled bladder at centre. An IVU is an X- ray image in which the urinary tract has been outlined by prior injection of a radio-opaque contrast medium that becomes concentrated in urine. An IVU may reveal the passage of urine from each kidney into the bladder, & is used to locate & assess lesions obstructing the urinary tract. Enlargement of the prostate, an accessory sex gland, occurs in elderly men; the subsequent obstruction to the neck of the bladder impairs urination.