Background
Studies demonstrated the significance of membranous urethral length (MUL) as a predictor of continence following robot-assisted radical prostatectomy (RARP). There are other magnetic resonance imaging (MRI) parameters that might be linked to continence outcome.
Objective
To evaluate the association between preoperative urethral parameters on MRI and continence outcome, to estimate the risk of incontinence using different cut-off values, and to assess interobserver variability in measuring urethral parameters.
Design, setting, and participants
Patients with localised prostate cancer who underwent RARP were retrospectively reviewed. Baseline patient characteristics, perioperative, and pathological outcomes were assessed. Continence was defined as no pad or a safety pad with <2 g/24 h pad weight.
Outcome measurements and statistical analysis
Several MRI variables were measured by a uroradiologist, a uro-oncology fellow, and a urologist. Binary logistic regression analyses were performed to identify predictors of incontinence. Interclass correlation was used to evaluate interobserver variability.
Results and limitations
A total of 190 patients met the study inclusion criteria. The mean MUL was 14.6 mm. Age and MUL were significantly associated with incontinence outcome. The area under the receiver operating characteristic curve for continence based on MUL was 0.78 at 12 mo. The risk of incontinence in patients with MUL of <10 mm was 27.8% (13.8% and 39.1% for patients aged <65 and >65 yr respectively). Conversely, the risk of incontinence with MUL >15 mm was 2.7% (1.5% and 4.5% for patients aged <65 and >65 yr, respectively). The concordance rate between different observers was 89% for coronal MUL, but 77%, 74%, and 62% for sagittal MUL, membranous urethral thickness, and intraprostatic urethral length, respectively.
Conclusions
This study confirmed the significance of MUL for the continence outcome following RARP. There was also excellent consistency in measuring MUL values between different observers.
Patient summary
Although further studies would be required to verify our findings, we support the significance of membranous urethral length in predicting the risk of incontinence and the need to incorporate it as part of preoperative assessment and counselling. This can reliably be measured by urologists and can further facilitate a patient-tailored approach to radical treatment of prostate cancer.
