Somatic and autonomic nerve density of the urethra, periurethral tissue, and anterior vaginal wall: an immunohistochemical study in adult female cadavers

Introduction and hypothesis: Retropubic procedures may disrupt nerves supplying the pelvic viscera; however, knowledge of pelvic neuroanatomy is limited. We sought to characterize somatic and autonomic nerve density within the urethra, periurethral tissue, and anterior vagina. Methods: Axial sections were obtained from pelvic tissue harvested from female cadavers ≤24 h from death at three anatomical levels: the midurethra, proximal urethra, and upper trigone. Periurethral/perivesical tissue was divided into medial and lateral sections, and the anterior vagina into middle, medial, and lateral sections. Double immunofluorescent staining for beta III tubulin (βIIIT), a global axonal marker, and myelin basic protein (MBP), a myelinated nerve marker, was performed. Threshold-based automatic image segmentation distinguished stained areas. Autonomic and somatic density were calculated as percentage of tissue stained with βIIIT alone, and with βIIIT and MBP respectively. Statistical comparisons were made using nonparametric Friedman tests. Results: Six cadavers, aged 22–73, were examined. Overall, autonomic nerve density was highest at the midurethral level in the lateral and middle anterior vagina. Somatic density was highest in the external urethral sphincter (midurethra mean 0.15%, SD ±0.11; proximal urethra 0.19%, SD ±0.19). Comparison of annotated sections revealed significant differences in autonomic density among the lateral, medial, and middle vagina at the midurethra level (0.71%, SD ±0.48 vs 0.60%, SD ±0.48 vs 0.70%, SD ±0.63, p=0.03). Autonomic density was greater than somatic density in all sections. Conclusions: Autonomic and somatic nerves are diffusely distributed throughout the periurethral tissue and anterior vagina, with few significant differences in nerve density among sections analyzed. Minimizing tissue disruption near urethral skeletal muscle critical for urinary continence may prevent adverse postoperative urinary symptoms.