Predictors of short and long term urinary incontinence after radical prostatectomy in prostate MRI: Significance and reliability of standardized measurements.

Purpose: To evaluate standardized measurements of the membranous urethra length (MUL), the membranous urethra angle (MUA) and the prostate's apex type (AT) among further clinical parameters as potential preoperative risk factors of urinary incontinence (UI) after radical prostatectomy (RP).

Method: Our institutional review board approved this retrospective single center study. 316 patients (mean age 65 years) underwent MRI at 3 T prior to prostatectomy. MUL, MUA and AT were measured according to a standardized approach on T2w- sagittal sequences. In a second reading the inter-rater agreement for the MUL was determined. Image findings and clinical data were correlated by logistic regression to UI as evaluated by a standardized questionnaire determining the number of necessary hygiene pads (HP) at three different time points with corresponding patient subsets (one week, six months and 12 months after RP).

Results: There was a significant impact of the MUL on postoperative UI with odds ratios (OR) of 0.8 [p < 0.001; confidence interval (CI) 0.73-0.91], 0.8 (p = 0.01; CI 0.68-0.94) and 0.7 (p < 0.01; CI 0.56-0.89) at the respective time points. No significant impact was demonstrated regarding the MUA and AT. Of all clinical parameters there was significant impact of the patients' age and the degree of nerve-sparing surgery. Inter-rater agreement with respect to the MUL was good with an intraclass correlation coefficient of 0.82. The mean deviation of raters measuring the MUL was 1.2 mm.

Conclusions: A shorter MUL in mpMRI should be considered as a risk factor of UI after RP. Standardized measurements enabling good inter-rater agreement should be considered for routine assessments to facilitate prospective classifications.