MATURATION OF THE EXTERNAL URINARY SPHINCTER - A COMPARATIVE HISTOTOPOGRAPHIC STUDY IN HUMANS

The developmental anatomy of the striated urinary sphincter remains co ntroversial and is scantly documented in children. We compared its str ucture and configuration in the fetus, infant and adult to determine a natomical differences among these groups. We removed 25 postmortem spe cimens from fetuses, infants and children, which were fixed and staine d for histological study. Ages ranged from 14 weeks of gestation to 12 years postpartum. Transverse and mid sagittal sections were obtained from the bladder neck to the membranous urethra in male and the whole urethra in female subjects. At the level of the membranous urethra in male and mid urethra in female subjects the striated muscle fibers com pletely encircle the urethra and join behind it to form a tail-like st ructure that runs posteriorly towards the perineal body. This structur e is mid sagittal in male and mediolateral in female subjects. At 3 to 4 months of life, at the level of the bulbourethral glands the tail d isappears; the striated sphincter becomes horseshoe-shaped and its 2 b ranches bifurcate posteriorly to envelop these glands. The urethral st riated sphincter consists of scantly dispersed muscle fibers in the fe tus. In young infants it becomes well defined in both sexes with the p resence of a tail-like structure that characterizes this age group. In older subjects this tail disappears and the sphincter assumes a horse shoe or omega-shaped configuration as splitting of the sphincter progr esses caudo-cranially with development. We attempt to determine whethe r the ring configuration of the voluntary sphincter contributes to hig h voiding pressures that are reported to occur in some newborns and in fants.