Membranous urethral length is the single independent predictor of urinary continence recovery at 12 months following Retzius-sparing robot-assisted radical prostatectomy

Abstract

The influence of anatomical parameters on urinary continence (UC) after Retzius-sparing robot-assisted radical prostatectomy (RS-RARP) remains uncharted. Our objective was to evaluate their association with UC at 3, 6 and 12 months post-operatively. Data from patients who underwent RS-RARP were prospectively collected. Continence was defined as no pad use. Anatomic variables were measured on preoperative magnetic resonance imaging (MRI). Regression analyses were performed to identify predictors of UC at each time point. We included 158 patients with a median age of 60 years, most of whom had a localized tumor (≤ cT2). On multivariate analyses, at 3 months post-surgery, urinary incontinence (UI) rises with age, odds ratio (OR) 1.07 [95% confidence interval (CI) 1.004-1.142] and with prostate volume (PV), OR 1.029 (95% CI 1.006-1.052); it reduces with longer membranous urethral length (MUL), OR 0.875 (95% CI 0.780-0.983) and with higher membranous urethral volume (MUV), OR 0.299 (95% CI 0.121-0.737). At 6 months, UI rises with PV, OR 1.033 (95% CI 1.011-1.056) and decreases with MUV, OR 0.1504 (95% CI 0.050-0.444). Significantly, at 12 months post-surgery, the only predictor of UI is MUL, OR 0.830 (95% CI 0.706-0.975), establishing a threshold associated with a risk of UI of 5% (MUL > 15 mm) in opposition to a risk of 25% (MUL < 10 mm). This single institutional study requires external validation. To our knowledge, this is the first prospective cohort study supporting MUL as the single independent predictor of UC at 12 months post-surgery. By establishing MUL thresholds, we enable precise patient counseling.

Keywords: Magnetic resonance imaging; Prognostic tool; Prostate cancer; Retzius-sparing robot-assisted radical prostatectomy; Urinary incontinence.

Fig. 1

a Midsagittal T2-weighted image. The yellow arrow displays maximum height of the prostate, measured from base to apex. The red arrow defines MUL, measured from the apex of the prostate to the upper border of penile bulb, at the dorsal side of the urethral lumen. b Axial T2-weighted image at maximal prostate width. The horizontal yellow double arrow shows maximal prostate width and the vertical yellow double arrow displays maximal prostate length. c Axial T2-weighted image immediately below the caudal margin of prostate apex. The horizontal red double arrow represents urethral width. The shorter and the longer yellow double arrows display the ILD and OLD, respectively. ILD inner levator ani muscle distance, MUL membranous urethral length, OLD outer levator ani muscle distance

Fig. 2

The blue line represents the probability of a patient being urinary continent at 12 months after Retzius-sparing robot-assisted radical prostatectomy, based on the logistic regression model. The orange dots represent the observed proportion of urinary continent patients, calculated according to 2.5 mm MUL intervals