Recovery of urinary function after radical prostatectomy: predictors of urinary function on preoperative prostate magnetic resonance imaging

Abstract

Purpose: We determined whether pelvic soft tissue and bony dimensions on endorectal magnetic resonance imaging influence the recovery of continence after radical prostatectomy, and whether adding significant magnetic resonance imaging variables to a statistical model improves the prediction of continence recovery.

Materials and methods: Between 2001 and 2004, 967 men undergoing radical prostatectomy underwent preoperative magnetic resonance imaging. Soft tissue and bony dimensions were retrospectively measured by 2 raters blinded to clinical and pathological data. Patients who received neoadjuvant therapy, who were preoperatively incontinent or had missing followup for continence were excluded from study, leaving 600 patients eligible for analysis. No pad use defined continent. Logistic regression was used to identify variables associated with continence recovery at 6 and 12 months. We evaluated whether the predictive accuracy of a base model was improved by adding independently significant magnetic resonance imaging variables.

Results: Urethral length and urethral volume were significantly associated with the recovery of continence at 6 and 12 months. Larger inner and outer levator distances were significantly associated with a decreased probability of regaining continence at 6 or 12 months, but they did not reach statistical significance for other points. Addition of these 4 magnetic resonance imaging variables to a base model including age, clinical stage, prostate specific antigen and comorbidities marginally improved the discrimination (12-month AUC improved from 0.587 to 0.634).

Conclusions: Membranous urethral length, urethral volume, and an anatomically close relation between the levator muscle and membranous urethra on preoperative magnetic resonance imaging are independent predictors of continence recovery after radical prostatectomy. The addition of magnetic resonance imaging variables to a base model improved the predictive accuracy for continence recovery, but the predictive accuracy remains low.

Figure 1

1. Symphysis angle defined as angle between the long axis of the symphysis pubis and the horizontal (Mid-sagittal T2-weighted image) 2. Apical depth of prostate: Vertical measurement from the most proximal margin of the symphysis pubis to the level of the distal margin of the prostatic apex (Mid-sagittal T2-weighted image) 3. Maximum height of the prostate measured from prostate base to apex at any level (Mid-sagittal T2-weighted image) 4. Lower conjugate of pelvic midplane defined as distance from lower inner symphysis pubis to sacrococcygeal junction (Mid-sagittal T2-weighted image) 5. Bony femoral width defined as bony width of the pelvis at the mid femoral head level (Axial T1-weighted image) 6. Urethra width defined as maximal diameter of the urethra (Axial T2-weighted image) 7. Outer levator distance defined as distance from the outer border of the levator muscles measured at the same level as inner levator distance (Axial T2-weighted image) 8. Inner levator distance defined as narrowest distance from the inner border of the levator muscle to the urethra below the caudal margin of the prostatic apex (Axial T2-weighted image) 9. Urethral length measured from the apex of the prostate to the base of the urethral bulbus (Coronal T2-weighted image) 10. Maximal prostate width (Axial T2-weighted image) 11. Maximal prostate length measured at the same level as maximal width measurement (Axial T2-weighted image)