Urethral calibre measurements on micturition cystourethrograms in adult males. Part two: Subvesical obstruction.

Urethral calibres were measured on six locations in 73 patients with obstruction of the bladder neck or prostatic urethra. The results indicate that the bladder outlet is compatible with normal micturition at calibres of 6 mm. or more and abnormally narrowed at 4 mm. or less. The very narrow overlapping area between the diameter values in normal and obstructed urethras makes MCU an accurate method of measurement the diagnosis of subvesical obstruction. More distal parts of the urethra although proven to be normal may appear on the roentgenograms as less distended than an abnormally narrowed bladder neck or prostatic urethra.