The pathophysiology of urethral prolapse has never been clearly elucidated. Following en bloc removal of the urethra, bladder, vagina, uterus and pelvic floor tissues from a 4-year-old burn victim with urethral prolapse at the time of death and from a female newborn cadaver, careful step-sectioning of the specimens at 5 mm. intervals for histological examination was performed. The anatomical defects of urethral prolapse noted were marked eversion of the urethral mucosa, vascular congestion of the 'corpus spongiosum urethrae muliebris', and a cleavage plane between the inner logitudinal and outer circular-oblique smooth muscle layers of the urethra. We propose that urethral prolapse results from poor attachments between the smooth muscle layers of the urethra in association with episodic increases in intra-abdominal pressure. A clinical review of 12 cases revealed that at least 8 (67 per cent) had antecedent episodes of marked increases in intra-abdominal pressure. Obliteration of the cleavage plane between the smooth muscle layers is important for successful treatment of this lesion.
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