Neuronal innervation of urethral and anal sphincters: surgical anatomy and clinical implications.

The present review describes the neuronal innervation of the external urethral and anal sphincters. A knowledge of this innervation helps in understanding the clinical symptoms of urinary and anorectal pathology, and in choosing the appropriate technique of nerve localization or block. An ability to locate the pudendal nerve, on the basis of surgically documented anatomy, has important diagnostic and therapeutic advantages. It can be used to study the integrity of pelvic floor muscles, in biofeedback training, nerve blocks, pudendal canal decompression, chronic stimulation trials to treat urinary or faecal incontinence, and in nerve conduction studies or evoked potential recordings. Furthermore, the superficial location of the sphincteric innervation in the perineum and ischiorectal fossa renders the nerve branches susceptible to injury during operative correction of urinary or faecal incontinence. Supported by a knowledge of anatomy, we can make firm recommendations on which to base safe surgical techniques that avoid damage to urethral and anal sphincteric innervation.