Muscular Structure at the Male Bladder Outlet Examined With Successive Celloidin-embedded Slices

ObjectiveTo re-examine the detailed anatomy of the muscular system at the bladder neck and proximal urethra in the male and to explore its function in urinary continence and micturition further.MethodsThe pelvic organs, including bladder, prostate, and rectum, were obtained from 20 formalin-fixed adult male cadavers and were removed from the pelvic cavity and embedded in celloidin in their entirety. The embedded block was cut into successive slices with an immersing-alcohol microtome.ResultsCircular muscle fibers of the detrusor at the bladder outlet consist of the anterior downward-projected circular muscle fibers of the bladder outlet (ADPC), the bilateral accumulated circular fibers, and the posterior circular fibers of the bladder outlet. Together, these fibers concentrically surround the internal urethral orifice and trigone muscle. The lower part of the ADPC surrounds the ventral surface of the proximal urethra. Longitudinal muscle fibers are radially inserted into the circular muscle around the internal urethral orifice. Numerous fibers from the ventral longitudinal muscle are inserted into the lower part of the ADPC. The upper part of the trigone muscle exists in bladder cavity; the lower part extends into the proximal urethra to surround the posterior and posterolateral surface of the urethra.ConclusionThe ADPC and the upward extension of the rhabdosphincter comprise the anterior fibromuscular stroma. The circular muscle of the bladder outlet may be responsible for closure; the longitudinal muscle of the bladder outlet may be responsible for opening of the internal urethral orifice and proximal urethra.