Multivariable models were adjusted for potential confounders, which included age at the time of the MRI, body mass index (BMI), last available PSA, presence of diabetes mellitus, hypertension, chronic obstructive pulmonary disease, use of 5 alpha reductase inhibitors, use of bladder medication, prostate volume, and the duration of surgery. In both univariable and multivariable analyses, longer MUL was significantly associated with lower odds of postoperative SUI. The multivariable model predicted a 13.9% reduction in the likelihood of SUI at one month with each millimeter increase in MUL. At three months, each millimeter increase was associated with a 23.1% reduction in the probability of SUI. At six months, each millimeter increase corresponded to a 35.0% decrease in the odds of post-operative SUI. No other covariates were significantly associated with six-month SUI in the multivariable model. At six months, patients with incontinence had a median MUL of 5.4mm compared with 8.2mm in continent patients. Corresponding numbers at three months were 6.3mm and 8.1 mm, at one month, 9.1mm and 9.8mm. The authors cite previously published studies that came to the same general conclusions, although measurements were somewhat different, which they ascribed to differences in patient populations or imaging methodologies.
After radical prostatectomy for cancer, MUL has been consistently associated with postoperative continence outcomes. Representative studies include a 2022 systematic review and meta-analysis2 of 50 studies, the conclusion being that greater MUL was prognostic for regaining urinary continence at 1, 3, 6, and 12 months postoperatively. This article also mentioned several other anatomical structures which at least in one study showed a significant correlation with later return to continence: prostate related parameters (greater depth, apical protrusion, larger intravesical protrusion, small dorsal vascular complex), urethral related parameters (thicker wall, severe fibrosis, smaller volume, larger preoperative angle between the prostate axis and membranous urethra, shorter minimal residual MUL) and six musculoskeletal related parameters (lower perfusion ratio, thinner levator ani muscle, larger inner or outer levator distance, shorter pelvic diaphragm length, and larger mid pelvic area). Greater MUL, however, was an independent prognostic factor. The authors noted that while other anatomical factors may be predictive, they require validation in prospective studies before incorporation into clinical risk models.
Another systematic review and meta-analysis published in 20233 examined the relationship between MUL and UI following robotic assisted radical prostatectomy and provided high level evidence that supported the predictive role of MUL. This included measurements at three months or less, and 12 months or longer, follow-up. Interestingly, in this study, the incontinence rates in 7 studies at 12 months were listed and, compared to more optimistic reports seen in studies trying to prove a different point, the rates were 9%, 7%, not reported, 48%, 50% low risk patients and 27% high risk patients, 9%, and 16%. Some of these studies suggested “cut points” for MUL for the prediction of incontinence risk. These ranged from 10.5mm to 14.27mm (note these are much higher than the median MUL of patients in the Lee et al article!). They also noted that some surgical techniques seem to preserve MUL better than others. They cited one study showing that bilateral nerve sparing results in a longer postoperative MUL on MRI than Non nerve sparing procedures.
A 2024 study from the Cleveland Clinic looked at preoperative MRI based anatomical predictors of early urinary continence following single port transvesical robotic assisted radical prostatectomy.4 They concluded that MUL alone was significantly associated with continence at three months and at one week. Several other parameters, including anterior posterior diameter of the prostate, prostate volume, and transverse diameter of the prostate, showed promise in predicting continence. In this series, each 1mm increase in coronal MUL was associated with a 27% increase in the odds of continence at three months. Their continence rates were 40% at one week, 71.7% by three months, And 93.2% by one year. Although the authors discussed correlations from other articles at 12 months, they did not include any statements that I could find regarding such correlations in their experience, although they clearly had patients who were followed out to 12 months.
So, what does all this mean, and why does endoscopic enucleation of the prostate (HoLEP) for benign prostatic obstruction demonstrate a similar association with MUL as radical prostatectomy for malignant disease? Lee et al. suggest this may relate to the broader range of instrument motion required during HoLEP, compared with conventional transurethral resection, which may increase the potential for intraoperative manipulation of the external sphincter. This suggests that procedures that impact the striated sphincter mechanism, particularly in patients with shorter baseline membranous urethral length, may be associated with a higher risk of postoperative stress urinary incontinence. However, this relationship may not apply uniformly across all procedures for benign prostatic obstruction.
These findings underscore the importance of preserving MUL and minimizing manipulation of the sphincteric complex between the prostate apex and the bulbar urethra. Additionally, there remains a need for standardized evaluation of preoperative parameters to better predict patient-specific risk of stress urinary incontinence across postoperative time points. Significant factors to consider would include not only MUL, but
- Patient age, general health, and baseline continence status
- Standardized techniques for measuring MUL and other quantifiable factors between the bladder neck and bulbous urethra
- Medical comorbidities that may predispose to urinary incontinence
- surgical technique
- Surgeon experience
- Perhaps some urodynamic factors, such as bladder compliance and some modification of urethral profilometry
Ideally, these and other clinical and anatomical variables could be integrated into predictive models to support more informed, patient- specific shared decision-making across prostate disease management.
Written by: Alan Wein, MD, PhD, FACS, Professor of Clinical Urology, Department of Urology, Desai Sethi Urology Institute (DSUI), University of Miami Miller School of Medicine, University of Miami Health Systems, Miami, FL
References:
- Lee N et al, Membranous urethral length as a predictor for urinary incontinence after holmium enucleation of the prostate for benign prostatic hyperplasia. World J Urology, 2026; 44:138, https://doi.org/101007/s00345-026-06232-4
- Van Dijk-de Haan MC et al, Value of different magnetic resonance imaging-based measurements of anatomical structures on preoperative prostate imaging and predicting urinary incontinence after radical prostatectomy in men with prostate cancer: a systematic review and meta-analysis. Eur Urology Focus, 2022; 8:1211-1225
- Mac Curtain BM et al, Membranous urethral length and urinary incontinence following robot assisted radical prostatectomy: a systematic review and meta-analysis. BJU int, 2023. doi:10.1111/bju.16170
- Ramos R et al, Preoperative prostate magnetic resonance imaging- based anatomical predictors of early urinary continence following single port transvesical robotic- assisted radical prostatectomy. Eur Urology Focus, 2024; 10: 1027-1033