Impact of Bladder Neck Angle Measured by Postoperative Magnetic Resonance Imaging on Midterm Recovery of Urinary Continence in Prostate Cancer Patients Undergoing Robot-Assisted Radical Prostatectomy

Introduction: MRI has helped clarify the relationship between pelvic anatomical structures and functional outcomes after robot-assisted radical prostatectomy (RARP). The objective of this study was to assess the impact of the bladder neck angle (BNA) measured by postoperative MRI on midterm recovery of urinary continence (UC) in patients undergoing RARP. Patients and Methods: This study retrospectively included 200 consecutive patients with prostate cancer who were treated by RARP and received MRI 3 months after RARP. Based on postoperative MRI, the BNA was measured as the angle between the anterior and posterior bladder walls. The midterm recovery of UC was defined as the use of either no pad or an occasional security pad at 6 months after RARP. Results: One hundred forty-four of the 200 patients (72.0%) achieved midterm recovery of UC and the median BNA was 70°. There were no significant differences in several parameters, including age, body mass index, total prostate volume, preservation of the neurovascular bundle, and postoperative membranous urethral length (MUL), between patients with BNA ≥70° and <70°. Of these parameters, only the BNA and postoperative MUL were independently associated with the midterm recovery of UC. The optimal cutoff points of the BNA and MUL (65° and 9 mm, respectively) were calculated by the receiver operating characteristics curve, and a scoring model for the prediction of midterm recovery of UC was developed according to the logistic regression analysis. This scoring model was demonstrated to be satisfactorily calibrated (p for Hosmer-Lemeshow test = 0.49) and provide good discrimination (area under the curve: 0.723; p < 0.001). Conclusions: These findings suggest that midterm recovery of UC after RARP is favorably affected by the large BNA and long postoperative MUL, and our scoring model can be used as a reliable tool for predicting the midterm continence status after RARP.