Urethral calibre measurements on micturition cystourethrograms in adult males. Part one: normal urethra.

The calibres of six different parts of the urethra were measured on micturition cystourethrograms in 92 normal adult males. The results are graphically displayed as frequency distribution histograms. The narrowest segment of the visualized urethra appeared to be the membranous part in 89 per cent of the cases. In the rest of the cases more distal regions were less distended than the membranous urethra. The bladder neck was always wider than the membranous part. Comparison of the diameters of the same segments measured in different planes suggest that during micturition the cross-sectional shape of the urethral tube is round.