NEUROANATOMY OF THE MALE RHABDOSPHINCTER

Objectives. The external striated urethral sphincter (rhabdosphincter) is a tubular muscle sleeve that extends from the prostate-membranous urethra and perineal membrane to the bladder neck. The male rhabdosphi ncter neuroanatomy remains unclear, and a better understanding of its innervation may provide insight into potential modifications of radica l pelvic surgery to improve urinary continence. Methods. Fresh cadaver ic dissections of 12 male hemipelves were undertaken to investigate th e neuroanatomy of the urinary rhabdosphincter. Results. Neuroanatomic courses of the nerve supply to the rhabdosphincter revealed that, in t he perineum, the perineal nerve (a terminal branch of the pudendal ner ve) provided branches directly to the bulbospongiosus muscle and the u rinary rhabdosphincter. In the pelvis, the course of the pelvic nerve was as follows: (1) arising from the inferior hypogastric plexus, it h ad a weblike course beneath the muscle fascia of the levator ani muscl e; (2) traveling posterolateral to the rectum, it gave many branches t hat perforated into the lateral rectum; and (3) at the level of the pr ostatic apex, still beneath the levator ani muscle fascia (superior fa scia), it sent multiple direct branches to the inferolateral aspect of urinary rhabdosphincter. The pudendal nerve traversed the pelvis in t he pudendal canal, and, before leaving the pelvis to enter the perineu m, it gave an intrapelvic branch that courses with the pelvic nerve to innervate the rhabdosphincter. Conclusions. Our understanding of the neuroanatomy of what may be the continence nerves has been improved by fresh cadaveric dissection. The rhabdosphincter receives nerve fibers from the pelvic nerve and dual innervation from an intrapelvic branch and a perineal branch of the pudendal nerve. Better understanding of these anatomic findings may have potential surgical significance with respect to improvement in postoperative urinary continence. (C) 1997, Elsevier Science Inc.