Midurethral support is also necessary for reflex closure of the urethra

The pathophysiology of female stress urinary incontinence (SUI) is far from unraveled. Capturing all aspects of this bothersome condition in one theory remains challenging. The well-known Hammock and Integral theories, both from the early 90's, were successful in explaining a large proportion of the observations made in clinical practice. Nevertheless, some (pre)clinical observations cannot be explained by the current understanding. One of the issues concerns the pressure transmission. Is this process really a passive mechanical action, or is an additional active mechanism responsible for urethral closure? The finding that an increase in urethral pressure sometimes precedes and exceeds the increase in intravesical pressure suggests the latter. This concept has never been incorporated in one of the existing theories describing SUI. This is remarkable as a lot of evidence has been generated in recent years that proves involvement of active components. This review aims to provide an additional theory in which an active reflex closure mechanism of the urethra is incorporated.

Recent as well as older publications from clinical and animal studies are included to support the hypothesis.

The smooth muscles of the urethra, the vascular bed, and the estrogen-influenced urethral mucosa, combined with striated muscle tone, contribute to the intra-urethral pressure. A passive transmission of force to the urethra exists only in the abdominal proximal third of the urethra. In the distal two thirds of the urethra an active closure mechanism is present, dependent on sufficient urethral support in the proper anatomical position. This active closure mechanism is generated by reflex contraction of striated muscles of the urethra and the pelvic floor.

Continence is a result of passive as well as active urethral closure mechanisms. The most important factor in female continence seems to be the proper functioning of an active reflex urethral closing mechanism.

Neurourology and urodynamics. 2018 Sep 06 [Epub ahead of print]

Allert M de Vries, Pieter L Venema, John P F A Heesakkers

Department of Urology, Radboud University Medical Centre, Nijmegen, The Netherlands., Department of Urology, Haga Hospital, The Hague, The Netherlands.