Pudendal Nerve Anatomy and Function

The pudendal nerve is a major somatic nerve of the sacral plexus originating from  S2-S4 nerve roots, innervates the external genitalia of both sexes and the skin around the anus, anal canal and perineum and supplying pelvic muscles, the external urethral sphincter and the external anal sphincter. It also carried carries sympathetic nerve fibers to the skin of the S2-S4 dermatomal region.

There are two pudendal nerves, each on the left and right side of the body.

The pudendal nerve is the main nerve of the perineum and pelvic floor. It gets damaged during childbirth or due to other causes leading to sensory loss or incontinence.

The pudendal block is an anesthetic procedure where the nerve may be temporarily blocked as part of an anesthetic procedure.

The pudendal canal that carries the pudendal nerve is also known by as Alcock’s canal, after Benjamin Alcock, an Irish anatomist who documented the canal in 1836. The term pudendal comes from Latin pudenda, meaning external genitals, derived from pudendum, meaning “parts to be ashamed of.

Anatomy and Course of Pudendal Nerve

The pudendal nerve arises from the anterior division of ventral rami of 2nd, 3rd and 4th sacral nerves of the sacral plexus.

The pudendal nerve may vary in its origins. It may actually originate off of the sciatic nerve. Sometimes dorsal rami of the S1 sacral nerve contribute fibers to the pudendal nerve, and even more rarely S5.

The nerve, after origin,  passes between the piriformis muscle and coccygeus (ischiococcygeus) muscles and leaves the pelvis through the lower part of the greater sciatic foramen.

The nerve emerges from the pelvis and courses through the gluteal region, turns forward around the sacrospinous ligament and leaves the gluteal region through the lesser sciatic foramen (between sacrotuberous and sacrospinous ligaments) to re-enter the pelvis.

After reentering the pelvis, it accompanies the internal pudendal artery and internal pudendal vein upwards and forwards along the lateral wall of the ischiorectal fossa, being contained in a sheath of the obturator fascia termed the pudendal canal, which lies on the obturator fascia above the falciform ridge along with the internal pudendal blood vessels.

Inside the pudendal canal, the nerve divides into branches, first giving off the inferior rectal nerve, then the perineal nerve, before continuing as the dorsal nerve of the penis (in males) or the dorsal nerve of the clitoris (in females).

Both terminal branches then enter the deep perineal pouch above and below the internal pudendal artery, respectively.

The inferior rectal branch arches through the ischioanal fossa and reaches the perianal skin, as well as the external anal sphincter, supplying both.

The dorsal nerve of the penis/clitoris accompanies the dorsal artery to supply the clitoris or skin of the penis. It gives no branches in the deep pouch.

The perineal branch gives off motor branches to superficial and deep perineal muscles and to the external urethral sphincter.

Relations

• Passes below the lower border of piriformis muscle as it passes through the greater sciatic foramen
• Lies on sacrospinous ligament just medial to the spine of ischium as it passes through the lesser sciatic foramen
• Travels through the pudendal canal with internal pudendal vessels

Variant anatomy

• contributions from S1 or S5 nerve roots
• The inferior rectal nerve can come directly from the sacral plexus or divide proximal to the pudendal canal
• Nerve plexus created by branches from inferior rectal and perineal nerves can form in ischiorectal fossa to supply external anal sphincter
• The additional accessory rectal nerve may be given from medial aspect of pudendal nerve at the level of sacrotuberous and sacrospinous ligaments which travels distally to perineum and levator ani.

Functions of Pudendal Nerve

The pudendal nerve has both motor and sensory functions. It lacks parasympathetic fibers but does carry sympathetic fibers.

Sensory Distribution

The pudendal nerve supplies sensation to the penis in males, and to the clitoris in females, which travels through the branches of both the dorsal nerve of the penis and the dorsal nerve of the clitoris. [ Responsible for the afferent component of penile erection and clitoral erection also]

The posterior scrotum in males and the labia in females are also supplied [ia the posterior scrotal nerves (males) or posterior labial nerves (females)]. The pudendal nerve is one of several nerves supplying sensation to these areas.

Sensation to the anal canal.

Supply to Muscles

• Muscles of the perineum and the pelvic floor
  • Bulbospongiosus
  • Ischiocavernosus
• Levator ani muscle (including the Iliococcygeus, pubococcygeus, puborectalis)
• Pubovaginalis in females or puboprostatic in males)
• External anal sphincter (via the inferior anal branch)
• External urethral sphincter

As it functions to innervate the external urethral sphincter it is responsible for the tone of the external urethral sphincter. The tone is mediated by acetylcholine release.

Clinical significance

Pudendal Nerve Block

It also called saddle nerve block, is a local anesthesia. It is used anesthetize the perineum during labor[  In this procedure, an anesthetic agent such as lidocaine is injected through the inner wall of the vagina about the pudendal nerve.

Pudendal Nerve Injury or Entrapment

The pudendal nerve can be compressed or stretched, resulting in temporary or permanent neuropathy. Pudendal nerve entrapment, also known as Alcock canal syndrome, is very rare and is associated with professional cycling.