The influence of bladder volume on the position and mobility of the urethrovesical junction

The influence of bladder volume on the position, mobility and funneling of the bladder neck and proximal urethra was determined by transperineal ultrasound in a prospective comparative clinical study at Dunedin Hospital, Dunedin, New Zealand. One hundred and nine women underwent urodynamic assessment, either as part of the investigation of urinary incontinence or as follow-up after incontinence-correcting surgery. Bladder neck descent, retrovesical angle, rotation of the proximal urethra, and simple and extensive funneling/opening of the proximal urethra on Valsalva maneuver were assessed using ultrasound imaging at approximately 50 ml bladder volume and maximum bladder capacity (mean 355 ml, range 125-470 ml). The position of the bladder neck at rest was slightly higher at 50 ml than at maximum capacity (50 ml: 2.6 ± 0.4 cm, max. cap. 2.5 ± 0.4 cm; P = 0.003) and it descended further with the Valsalva maneuver (50 ml: 1.9 ± 1.2 cm, max. cap. 1.7 ± 1 cm; P = 0.004). There was also a higher degree of urethral rotation (50 ml: 41 ± 30°, max. cap. 39 ± 20°) with an empty bladder (P = 0.072). As regards funneling of the bladder neck on Valsalva, equivalent results were obtained for 90 patients. In 19 cases there were discrepancies (Cohen's κ 0.64). For extensive funneling to the midurethra the respective numbers were 83 and 26 (κ 0.41). Generally simple and extensive funneling was more frequently seen with a full rather than an empty bladder, simple funneling being diagnosed in an additional 14 cases (P = 0.06) and extensive funneling in an additional 19 (P = 0.03). It was concluded that bladder filling influences the position and mobility of the bladder neck and the proximal urethra, which are both more mobile when the bladder is nearly empty. Funneling of the proximal urethra, however, is more easily observed with a full bladder. Imaging of the lower urinary tract should be undertaken at defined bladder volumes.