Investigating The Mechanism Underlying Urinary Continence Using Dynamic-MRI After Retzius-sparing Robot-assisted Radical Prostatectomy

Retzius-sparing robot-assisted radical prostatectomy (RS-RARP) has been reported to exhibit better postoperative urinary continence compared to conventional RARP (C-RARP) via the anterior approach, but the reasons behind this are unknown. The early postoperative urinary incontinence and anatomical differences were compared between 51 cases each of C-RARP and RS-RARP, which were selected via propensity score matching. Dynamic-MRI was performed before and after surgery to investigate the pelvic anatomical changes under abdominal pressure. The median urine loss ratio in the early postoperative period was 11.0% and 1.0% for C-RARP and RS-RARP, respectively. Postoperative MRI revealed the anterior bladder wall after RS-RARP was fixed in a high position compared to C-RARP. Dynamic-MRI after C-RARP showed cephalocaudal compression of the bladder during abdominal pressure caused expansion of the membranous urethra and the urine flowed out. In RS-RARP cases, the rectum moved forward during abdominal pressure to compress the membranous urethra by closing it from behind, as was observed preoperatively. This was the first study using dynamic-MRI which revealed the importance of a high attachment of the anterior bladder wall for the urethral closure mechanism during abdominal pressure. RS-RARP, which can completely preserve this mechanism, was the least likely to cause stress urinary incontinence.