Neuroanatomy of the pelvis

Abstract

PURPOSE: Urinary dysfunction remains a common complication of radical pelvic surgery, particularly after abdominoperineal resection. In treating rectal carcinoma, the extent of primary resection and lymphadenectomy are major determinants in the degree of postoperative urologic morbidity. METHODS. Twelve male and eight female hemipelves from fresh cadavers were dissected with reference to the neuroanatomy of the lower genitourinary tract. These cadavers were dissected within twelve hours of thaw from frozen state. The cadavers were hemisected at the level of the sacral promontory for better exposure of neural trunks and vascular structures leading into the pelvis. These structures were followed down sequentially into the true pelvis, using magnified dissection under operating microscope or loupe dissection or both. RESULTS: Coordinated lower urinary tract function relies on both autonomic and somatic nerve activity. Emanating from the inferior hypogastric plexus, the pelvic nerve supplies sympathetic and parasympathetic innervation to the pelvic viscera. The course of the pelvic nerve is as follows: 1) from the inferior hypogastric plexus, it has multiple branches forming a web-like complex within the endopelvic fascial sleeve, some of which innervate the bladder detrusor; 2) a main branch traveling inferolateral to the rectum remains deep to the fascia of the levator ani muscle and courses to the external urinary sphincter; 3) at the level of the prostatic apex (or bladder neck in females), this pelvic nerve branch sends direct branches to the urinary sphincter. The pudendal nerve traverses the pelvis in the pudendal canal, and before leaving the pelvis to enter the perineum, it gives an intrapelvic branch that courses alongside the ischium to enter the external urinary sphincter. In the ischiorectal fossa, terminal branches of the pudendal nerve (i.e., perineal nerve) can be seen inserting into the urinary sphincter. CONCLUSIONS. Urinary retention and urinary incontinence represent two distinct urologic complications after abdominoperineal resection. Injury to detrusor branches of the pelvic nerve can cause detrusor denervation and urinary retention. In addition, injury to intrapelvic branches of the pelvic and pudendal nerves to the urinary sphincter can result in intrinsic sphincter deficiency and urinary incontinence. A better understanding of the neuroanatomy of the lower genitourinary tract can give a physiologic basis for clinical findings of postoperative voiding dysfunction and may help the surgeon refine surgical technique by more precisely determining resection limits to minimize urologic complications.