Urethral Closure Mechanism Caused by Prostate Rotation During Abdominal Pressure in Men: A Dynamic Magnetic Resonance...

To elucidate the urethral closure mechanism during abdominal pressure in men, we investigated changes in pelvic anatomy during abdominal pressure using dynamic Magnetic Resonance Imaging (MRI).

This study retrospectively analyzed data from 145 patients scheduled for robot-assisted radical prostatectomy at Kanazawa University Hospital from 2016 to 2022. Preoperative dynamic MRI was used to take measurements at several anatomical points to assess changes in pelvic anatomy during abdominal pressure.

Dynamic MRI measurements during abdominal pressure revealed that the prostate apex rotates anteriorly at an average of 5.6°, and the internal urethral orifice shifts dorsally. Additionally, the prostate apex moves 1.2 mm toward the pubic bone. Conversely, the distal end of the membranous urethra shifts 0.9 mm dorsally during abdominal pressure. Consequently, a misalignment between the prostate apex and the membranous urethra is observed, resulting in the closure of the anterior-posterior direction of the proximal membranous urethra that may contribute to urethral closure during abdominal pressure.

These results may suggest that prostate rotation during abdominal pressure creates a step-like displacement at the proximal membranous urethra, which could contribute to urethral closure in men with an intact prostate. Dynamic MRI provides anatomical evidence supporting a complementary role of prostate motion in this mechanism.

Not applicable. This study was conducted prospectively with written informed consent and institutional ethical approval; however, it was not designed as a clinical trial because it was a non-interventional observational study in which a specialized MRI protocol was added to standard clinical imaging without any therapeutic intervention or treatment allocation.