Magnetic resonance imaging of the male pelvic floor: the anatomical configuration and dynamic movement in healthy men.

The male pelvic organs and the rhabdosphincter were visualized using magnetic resonance imaging (MRI) in five young male volunteers (mean age, 25.6 years). The prostate was crescent-shaped in three subjects and doughnut-shaped in two subjects. The external urethral sphincter (EUS) was located anterior to and lateral to the urethra but was rare on the rectal side. The membranous urethral length measured 28-35 mm (average, 31.0 mm). The pubourethral portion of the levator ani embraced the urinary bladder, the prostate, and the membranous urethra, and the most distal portion of the levator was thickened. During anal contraction, the EUS became thinner on both coronal and sagittal images and the levator was approximated closer to the urethra. Consequently, the prostate and the bladder base were elevated and the membranous urethra was elongated by 0-12mm (average, 5.6 mm). On sagittal images, the prostate, the membranous urethra, and the rectum were pulled closer to the pubic bone by anal contraction and the retropubic area became narrower. This study clearly demonstrated that MRI was useful in examining the anatomical configuration of the male pelvic floor and its dynamic movement during anal contraction.