Urethral closure mechanism dysfunction in female stress urinary incontinence (SUI) is poorly understood. We aimed to quantify these mechanisms through changes in urethral shape and position during squeeze (voluntary closure) and Valsalva (passive closure) via endovaginal ultrasound in women with varying SUI severity.
In this prospective cohort study, 76 women who presented to our tertiary center for urodynamic testing as preoperative assessment were recruited. Urodynamics were performed according to International Continence Society criteria. Urethral pressures were obtained during serial Valsalva maneuvers. Urethral lengths, thicknesses, and angles were measured in the midsagittal plane via dynamic anterior compartment ultrasound. Statistical shape modeling was carried out by a principal component analysis on aligned urethra shapes.
Age, parity, and BMI did not vary by SUI group. Ultrasound detected a larger retropubic angle, urethral knee-pubic bone angle (a novel measure developed for this study), and infrapubic urethral length measurements at Valsalva in women with severe SUI (p = 0.016, 0.015, and 0.010). Shape analysis defined increased “c” shape concavity and distal wall pinching during squeeze and increased “s” shape concavity and distal wall thickening during Valsalva (p < 0.001). It also described significant urethral shape differences across SUI severity groups (p < 0.001).
Dynamic endovaginal ultrasound can visualize and allow for quantification of voluntary and passive urethral closure and variations with SUI severity. In women with severe SUI, excessive bladder neck and distal urethra swinging during Valsalva longitudinally compressed the urethra, resulting in a proportionally thicker wall at the mid-urethra and urethral knee.