MRI-derived bladder wall thickness as an independent predictor of acute urinary retention in men with benign prostatic obstruction.

PURPOSE: To evaluate MRI-derived bladder wall thickness (BWT) as a predictor of acute urinary retention (AUR) in men with lower urinary tract symptoms (LUTS) suggestive of benign prostatic obstruction, and to assess the complementary value of a novel intravesical prostatic length-to-prostate sagittal length (IPL/PSL) ratio. METHODS: This retrospective study included 276 men with LUTS who underwent multiparametric MRI. BWT was measured at three standardized locations under controlled bladder filling conditions (250-300 mL), and the IPL/PSL ratio was calculated as a normalized index of intravesical prostatic protrusion. Interobserver agreement was assessed using the intraclass correlation coefficient (ICC). Multivariable logistic regression and ROC curve analysis were performed to identify independent predictors of AUR. RESULTS: Interobserver agreement was excellent (ICC: BWT 0.93, IPL 0.89, PSL 0.91). Patients who developed AUR had significantly higher BWT and IPL/PSL ratios than those without AUR (both p < 0.001). BWT was independently associated with AUR in multivariable analysis (OR 1.59 per 1-mm increase, 95% CI 1.35-1.89; p < 0.001) and demonstrated good discriminative ability (AUC 0.794). The IPL/PSL ratio did not reach statistical significance (OR 4.50, 95% CI 0.97-20.8; p = 0.054). The combined model achieved an AUC of 0.81. CONCLUSIONS: MRI-derived BWT was independently associated with AUR and may reflect cumulative detrusor remodeling secondary to chronic bladder outlet obstruction. The IPL/PSL ratio did not reach independent significance; however, its borderline association warrants evaluation in larger prospective studies. MRI-based morphological parameters may serve a complementary role in risk stratification in patients who have already undergone imaging.