The Pudendal nerve (S2-4) is the lowermost branch of the sacral plexus. It coarses through the greater sciatic foramen, passes around the ischial spine through the lesser sciatic foramen into the pudendal canal of the ischioanal fossa. The pudendal nerve divides into the inferior rectal and perineal branches and the dorsal nerve of the penis (clitoris).
A transvaginal pudendal nerve block is accomplishes by proper identification of the ischial spine and the sacrospinous ligament. The area is infiltrated with anesthetic, ensuring that the needle has not pierced an internal pudendal vessel with risk of hematoma formation. The pudendal nerve provides motor and sensory innervation to the perineum. It leaves the pelvis via the greater sciatic foramen, wraps around the external surface of the ischial spine, and enters the pelvis again through the lesser sciatic foramen. The fascia of obturator internus forms a canal (pudendal or Alcock's) for the passage of the pudendal nerve in the lateral wall of the ischioanal fossa. The terminal branches and their territories of distribution would be affected in a pudendal block (namely; inferior rectal, perineal, and dorsal nerve of the clitoris).