Pudendal Nerve

Origin

The pudendal nerve is the major somatic nerve of the perineum and is formed on the anterior surface of the lower part of the piriformis muscle, from the anterior divisions of the anterior rami of S2-S4 nerves.

Course

Following its origin from the anterior divisions of the anterior rami of S2-S4 nerves, the pudendal nerve leaves the pelvic cavity through the greater sciatic foramen, inferior to the piriformis muscle, and enters the gluteal region.

It then courses around the sacrospinous ligament, and ischial spine, passes through the lesser sciatic foramen to enter the anal triangle of the perineum (Wallner et al., 2008). It is accompanied throughout its course by the internal pudendal artery and vein.

The nerve travels along the lateral wall of the ischioanal fossa in the pudendal canal, which is a tubular compartment formed in the fascia that covers the obturator internus muscle. The pudendal canal also contains the internal pudendal artery and veins.

Branches

The pudendal nerve has the following three major terminal branches, all of which are accompanied by the branches of the internal pudendal artery.

Often there are multiple Inferior anal (rectal) nerves. They penetrate the fascia of the pudendal canal and courses medially across the ischioanal fossa to innervate the external anal sphincter and related regions of the levator ani muscles. The nerve is also general sensory for the skin of the anal triangle.

The Perineal nerve passes into the urogenital triangle and gives rise to motor and sensory cutaneous branches.

The posterior nerve of the penis or clitoris enters the deep perineal pouch. It passes along the lateral margin of the pouch and exits it by passing inferiorly through the perineal membrane, just inferior to the pubic symphysis, and meets the body of the clitoris or the penis. It courses along the posterior surface of the body to reach the glans. The posterior nerve is sensory to the penis and clitoris, particularly to the glans.

Supplied Structures

The inferior anal (rectal) nerve innervates the external anal sphincter and related regions of the levator ani muscles. The nerve is general sensory for the skin of the anal triangle.

The perineal nerve supplies motor branches to skeletal muscles in the superficial and deep perineal pouches (ischiocavernosus, bulbospongiosus, superficial transverse perineal muscle, deep transverse perineal muscle, external urethral sphincter, compressor urethrae). It also provides sensory innervation to the skin of the urogenital triangle. The largest sensory branch is the dorsal scrotal nerve (males) or the posterior labial nerve (females).

In some rare cases, both the perineal and inferior rectal nerves enter a plexus inside the ischiorectal fossa to provide a combined motor innervation to the external anal sphincter muscle (Mahakkanukrauh, Surin and Vaidhayakarn, 2005).

The dorsal nerve of the penis and clitoris is sensory to the penis and clitoris, particularly to the glans.

List of Clinical Correlates

—Pudendal nerve block (for local anesthesia)

—Caudal epidural block (Schraffordt et al., 2004)

—Chronic pelvic pain syndrome (Moore, Dalley and Agur, 2013)

References

Mahakkanukrauh, P., Surin, P. and Vaidhayakarn, P. (2005) 'Anatomical study of the pudendal nerve adjacent to the sacrospinous ligament', Clin Anat, 18(3), pp. 200-5.

Moore, K. L., Dalley, A. F. and Agur, A. M. R. (2013) Clinically Oriented Anatomy. Clinically Oriented Anatomy 7th edn.: Wolters Kluwer Health/Lippincott Williams & Wilkins.

Schraffordt, S. E., Tjandra, J. J., Eizenberg, N. and Dwyer, P. L. (2004) 'Anatomy of the pudendal nerve and its terminal branches: a cadaver study', ANZ J Surg, 74(1-2), pp. 23-6.

Wallner, C., van Wissen, J., Maas, C. P., Dabhoiwala, N. F., DeRuiter, M. C. and Lamers, W. H. (2008) 'The contribution of the levator ani nerve and the pudendal nerve to the innervation of the levator ani muscles; a study in human fetuses', Eur Urol, 54(5), pp. 1136-42.