The pudendal nerve (S2-S4) divides in the pudendal canal (Alcock's canal) into three terminal branches: the inferior rectal nerve (supplies the external anal sphincter, perianal skin, and lower anal mucosa); the perineal nerve (divides into deep branch supplying the external urethral sphincter, bulbospongiosus, ischiocavernosus, and superficial transverse perineal, and superficial branch to posterior scrotum/labia majora skin); and the dorsal nerve of the penis/clitoris (sensory to the dorsal penis or clitoris).
Understanding pudendal nerve terminal branch anatomy guides pudendal neuralgia diagnosis and surgical decompression. The inferior rectal branch is the nerve injured during obstetric trauma and haemorrhoidectomy — its injury contributes to faecal incontinence. The dorsal nerve of the penis is the nerve of penile erection sensation and is at risk in urethral surgery and penile prosthesis implantation. Pudendal nerve terminal branch blocks under CT or ultrasound guidance target the specific branch causing pain (inferior rectal for perianal pain, perineal branch for vulvodynia, dorsal penile nerve for post-vasectomy pain).
Prolonged or instrumental vaginal delivery stretches the inferior rectal branch of the pudendal nerve beyond its physiological limit, producing external anal sphincter denervation and reduced sphincter pressure that contributes to post-partum faecal incontinence; pudendal nerve terminal motor latency testing and anal manometry assess the degree of denervation.
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