What is normal bladder neck anatomy?

Functional anatomy of the bladder neck and proximal urethra has been studied extensively because of the belief that it is important for urinary continence. The aim of this study was to explore the limits of normality for pelvic floor ultrasound parameters of bladder neck and urethral mobility associated with stress urinary incontinence (SUI) and urodynamic stress incontinence (USI).

A retrospective study was conducted on 589 women seen for urodynamic testing in a tertiary urogynaecology clinic. All women were assessed following a protocol including interview, clinical examination, flowmetry, urodynamic testing and 4D pelvic floor ultrasound. Volume data sets were analysed offline to assess for bladder neck descent (BND), urethral rotation and the retrovesical angle (RVA) on maximal Valsalva.

After excluding women with previous incontinence or prolapse surgery, 429 datasets were available. SI was significantly associated with the RVA (p = 0.033) and BND (p = 0.036); USI was associated with urethral rotation (p = 0.021) and BND (p < 0.001). On multivariate logistic regression analysis, controlling for confounders including age, BMI, parity, previous hysterectomy and maximal urethral pressure, the association between SUI and BND remained significant (OR [per 10 mm] = 1.23; 95 % CI: 1.01 to 1.51; p = 0.043), as did the association between USI and BND (OR [per 10 mm] = 1.58; 95 % CI: 1.3 to 1.91; p < 0.001). ROC statistics for BND suggested a cut-off of 25 mm in describing the limit of normality.

Measures of functional bladder neck anatomy are weakly associated with SUI and USI (with association between BND and USI being the strongest). It is suggested that a BND of 25 mm or higher be defined as abnormal ("hypermobile") on the basis of its association with USI.