MP88-06 THE MECHANISM OF ACTION OF THE MALE TRANSOBTURATOR SLING IS VIA INCREASED FUNCTIONAL LENGTH OF THE MEMBRANOUS URETHRA: A PROSPECTIVE, CONTROLLED STUDY USING DYNAMIC MRI
INTRODUCTION AND OBJECTIVES
The precise mechanism by which the AdVance(TM) transobturator sling (TOS) improves continence is unknown. Postulated mechanisms of action include changes in urethral mobility or an increase in functional membranous urethral length (FUL). Using dynamic MRI, we sought to determine how anatomic and functional relationships change in the male urethra after TOS surgery.
METHODS
We conducted a prospective study of males undergoing TOS from 2010 to 2014. Males with SUI after radical prostatectomy (RP) who were scheduled for TOS were enrolled. Patients underwent pad weight testing, voiding diary, urodynamics, and cystoscopy preoperatively. Dynamic MRI was performed before and after TOS. On matched pre- and post-operative sagittal T2 weighted images using a 3T MR system, the following measurements were obtained both at rest (R) and Valsalva (V): 1) distance from bladder neck BN to pubic symphysis (termed AP); 2) distance from BN to urethra at the pubococcygeal line (termed CC); and 3) distance from BN to urethra at the penile bulb (termed FUL). A group of patients who underwent RP with no SUI on pad weight testing underwent MRI post-RP and served as controls.
RESULTS
A total of 34 (20 cases, 14 controls) patients were enrolled in the study. All patients who underwent TOS had improvement in continence (12 used zero pads, 5 used 1 pad/day). Prior to TOS, there was a significant difference in rest and Valsalva CC but not AP distance when compared to non-leaking controls (mean case CC R 0.42cm and V 0.32cm vs. control CC R 1.06cm and V 1.09cm, resp, p < 0.05). Post-TOS, neither R and V AP nor R and V CC were different when compared to non-leaking controls. When comparing post-TOS to pre-TOS among the cases, there was a trend towards a difference in mean CC distance at rest and Valsalva (R pre 0.42cm vs post 0.63cm, p = 0.09; V pre 0.32cm vs post 0.54cm, p = 0.13). To assess urethral mobility, we looked at the rest to Valsalva change in AP and CC distance before and after TOS, and there was no significant difference in either measurement (mean difference in R-to-V AP pre 0.21cm vs post 0.3cm, mean difference in R-to-V CC pre 0.1cm vs post 0.09cm). However, the pre-sling cases had a shorter rest FUL when compared to controls (1.27 vs 1.92cm, p <0.05) and the post-TOS FUL increased significantly (1.27 vs 1.53 cm, p <0.05) and approximated the FUL found in dry controls.
CONCLUSIONS
The mechanism of action of the male TOS appears to be via an increase in functional urethral length rather than changes in urethral mobility.
