Contribution of Retzius-sparing robot-assisted radical prostatectomy to the mechanism of urinary continence as demonstrated by dynamic MRI.

Retzius-sparing robot-assisted radical prostatectomy (RARP) has been reported to exhibit better postoperative urinary continence, but the reasons behind this are unknown. This study included 254 cases who underwent RARP and underwent postoperative dynamic MRI. We measured the urine loss ratio (ULR) immediately after postoperative urethral catheter removal and investigated its affecting factors and the mechanisms. Nerve-sparing (NS) techniques was performed in 175 (69%) unilateral and 34 (13%) bilateral cases, whereas Retzius-sparing in 58 (23%) cases. The median ULR early after indwelling catheter removal in all patients was 4.0%. The multivariate analysis was performed on factors that reduce ULR and found that the following factors were associated with ULR: younger age, NS and Retzius-sparing, which were significant. Additionally, dynamic MRI findings showed that membranous urethral length and the anterior rectal wall movement toward the pubic bone during abdominal pressure were significant factors. The movement observed on the dynamic MRI during abdominal pressure was thought to reflect an effective urethral sphincter closure mechanism. Long membranous urethral length and an effective urethral sphincter closure mechanism during abdominal pressure were considered effective for favorable urinary continence after RARP. NS and Retzius-sparing were clearly shown to have an additive effect in preventing urinary incontinence.