Stimulation of the Neurovascular Bundle Results in Rhabdosphincter Contraction in a Proportion of Men Undergoing Radical Prostatectomy

Abstract

To use nerve conduction studies to clarify the functional innervation of the male urethral rhabdosphincter (RS). In particular, to test the hypothesis that in some men, fibers of the neurovascular bundle supply the RS. These fibers may be at risk during radical prostatectomy. Men undergoing robot-assisted radical prostatectomy for clinically localized prostate cancer were included. Men with a history of pelvic surgery and/or radiation and/or trauma, obesity, or neurological diseases were excluded. Nerve conduction studies were performed before and after prostate removal. The St. Mark's pudendal electrode was used for pudendal (control) stimulation. The ProPep Nerve-Monitoring System (ProPep Surgical, Austin, TX) was used to stimulate the neurovascular bundle at the level of the prostate base, mid, and apex. ProPep needle electrodes inserted into the RS were used to measure evoked compound motor action potential response. Results were only included if a valid pudendal control was elicited. Seventeen men in total underwent investigation. Valid measurements were obtained after initial quality control in seven. In two cases, evidence of sphincteric activation was observed, providing evidence to support neurovascular bundle innervation of the RS. In the other five patients, no intrapelvic nerve supply was demonstrated. Somatic nerve supply to the RS is variable. Direct intrapelvic supply to the RS may exist in some men. This may be one explanation as to why some patients unexpectedly develop severe urinary incontinence postoperatively despite technically satisfactory surgery. Further research is required to validate our findings.