Anatomy Atlas

Pudendal nerve

Nervus pudendus
NerveHigh-yielddraftNeuro

Main somatic nerve of the perineum (S2–S4), supplying the external anal and urethral sphincters, the perineal muscles and perineal skin. It is blocked at the ischial spine in labor and can be stretched in childbirth or entrapped in cyclists.

Core anatomy

Location

Leaves the pelvis, curves around the ischial spine, and runs forward in the lateral wall of the ischioanal fossa to the perineum.

Root values

Ventral rami of S2, S3 and S4 (from the sacral plexus).

Origin

Sacral plexus, on the posterior pelvic wall.

Course

Leaves the pelvis through the greater sciatic foramen below piriformis, crosses the back of the sacrospinous ligament just medial to the ischial spine (medial to the internal pudendal vessels), and re-enters the perineum through the lesser sciatic foramen. It then runs in the pudendal (Alcock) canal, a split in the obturator internus fascia, with the internal pudendal vessels.

Branches
  • Inferior rectal (anal) nerve: crosses the ischioanal fossa to the external anal sphincter, the lower anal canal (below the pectinate line) and perianal skin
  • Perineal nerve: superficial branches (posterior scrotal/labial nerves) to the skin; deep branches to bulbospongiosus, ischiocavernosus, the transverse perineal muscles and the external urethral sphincter
  • Dorsal nerve of the penis or clitoris: sensory to the glans and most of the shaft
Motor

External anal sphincter, external urethral sphincter, perineal muscles, and part of levator ani.

Sensory

Most of the perineal skin, the posterior scrotum or labia, the penis or clitoris, the lower quarter of the vagina, and the anal canal below the pectinate line.

Relations

The internal pudendal vessels run with it throughout. The anterior perineum (mons, anterior scrotum/labia) is supplied instead by the ilioinguinal and genitofemoral nerves, and the lateral perineum by the posterior femoral cutaneous nerve.

Notes

"S2, 3, 4 keep the poop off the floor" (and the pee): pudendal and pelvic splanchnic nerves serve continence.

Muscles innervated

  • Pelvic diaphragm — Nerve to levator ani (direct branches of the ventral rami of S3–S4), with contributions from the inferior rectal and perineal branches of the pudendal nerve. Coccygeus: S3–S4 ventral rami.

Other structures innervated

Found in

Mentioned in

Generated automatically from links in other entries.

Perineum: urogenital and anal triangles (inferior view)Diamond-shaped perineum bounded by the pubic symphysis, ischiopubic rami, ischial tuberosities, sacrotuberous ligaments and coccyx. A line between the ischial tuberosities separates the anterior urogenital triangle (urethra and vagina) from the posterior anal triangle (anus and ischioanal fossae). The perineal body lies at the center. The pudendal canal runs in the lateral wall of each ischioanal fossa.Pubic symphysisIschiopubic ramusIschialtuberosityIschialtuberosityUrogenital triangle(perineal membrane,superficial & deep pouches)UrethraVagina (♀)Perineal bodyIschioanalfossaIschioanalfossaAnus + externalanal sphincterPudendal canal(pudendal n. +int. pudendal vessels)Inferior rectal n.Sacrotuberous lig.Anal triangleCoccyxAnterior ↑ (inferior view, lithotomy)Dashed line: between the ischial tuberosities

Swipe sideways to see the whole diagram →

Perineum: urogenital and anal triangles. Inferior view with the patient in lithotomy (anterior at the top). A line between the ischial tuberosities divides the urogenital triangle from the anal triangle; the pudendal canal runs in the lateral wall of each ischioanal fossa.
Original schematic, created for this atlas.
Lateral view of the right pelvis showing the sacral plexus and the pudendal nerve with its perineal, inferior rectal and dorsal penile branches
Sacral plexus and pudendal nerve (right side) with its inferior rectal, perineal and dorsal penile branches.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 837. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))
Dissection of the lateral pelvic wall showing the sacral plexus, pudendal nerve, sympathetic trunk and visceral branches beside the bladder, prostate and rectum
Lateral pelvic wall showing the pudendal nerve leaving the sacral plexus.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 829. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Pudendal nerve block PANCE

Mechanism / lesion

Local anesthetic injected transvaginally through the sacrospinous ligament just medial and posterior to the ischial spine, where the nerve crosses. Aspirate first to avoid the internal pudendal vessels.

Classic presentation

Anesthetizes most of the perineum for the second stage of labor, forceps delivery or perineal repair. The anterior perineum (ilioinguinal/genitofemoral) and lateral perineum (posterior femoral cutaneous) still need local infiltration.

Obstetric pudendal neuropathy

Mechanism / lesion

Stretch injury during prolonged second stage or instrumental delivery.

Classic presentation

Fecal and/or urinary incontinence with reduced perineal sensation; usually improves over months.

Pudendal neuralgia (entrapment)

Mechanism / lesion

Compression between the sacrotuberous and sacrospinous ligaments or in the pudendal canal; associated with prolonged cycling and pelvic surgery.

Classic presentation

Burning pain in the perineum, genitals or rectum that is worse sitting and relieved by standing, lying down or sitting on a toilet seat; no objective sensory loss (Nantes criteria). A diagnostic pudendal block helps confirm it.

High-yield PANCE pearls

  • Pudendal = S2–S4; supplies the external anal and urethral sphincters and perineal skin.
  • Pudendal block: needle just medial to the ischial spine through the sacrospinous ligament.
  • Perineal pain worse with sitting in a cyclist → pudendal neuralgia.
  • Saddle anesthesia + loss of anal tone → cauda equina (S2–S5) — not an isolated pudendal problem.

Imaging anatomy

CT

CT (or ultrasound/fluoroscopy) guides pudendal nerve blocks at the ischial spine or in the pudendal canal.

MRI

MR neurography can show the nerve and sites of compression; MRI excludes masses along its course.

Physical exam

Surface landmarks

The ischial spine, palpable transvaginally or transrectally at about 4 and 8 o'clock, marks where the nerve crosses the sacrospinous ligament.

Palpation

Tenderness over the ischial spine on internal exam supports pudendal entrapment.

Strength / function testing

Perianal and perineal pinprick and light touch (S3–S5 "saddle"), anal wink (anocutaneous reflex), bulbocavernosus reflex and DRE for resting tone and voluntary anal contraction (a key part of the ASIA exam in spinal cord injury).

Self-quiz

Q1.

During a transvaginal pudendal block for a forceps delivery, local anesthetic is injected just medial to the ischial spine. After the block the patient still feels pain at the anterior labia. Which nerve supplies that area?

Show answer

B

The anterior labia (and mons) are supplied by the ilioinguinal nerve and the genital branch of the genitofemoral nerve (L1), which a pudendal block does not reach, so local infiltration is added.

Q2.

Which muscle is supplied by the inferior rectal branch of the pudendal nerve?

Show answer

B

The inferior rectal nerve supplies the voluntary external anal sphincter and perianal skin. The internal sphincter is smooth muscle under autonomic control; bulbospongiosus is supplied by the perineal nerve.

Q3.

The pudendal nerve re-enters the perineum through which opening?

Show answer

C

The pudendal nerve leaves the pelvis through the greater sciatic foramen below piriformis, curves around the ischial spine, and enters the perineum through the lesser sciatic foramen into the pudendal canal.

Q4.

A 45-year-old competitive cyclist has burning perineal pain that is worse when sitting and relieved by standing or sitting on a toilet seat. Sensation is normal on exam. What is the most likely diagnosis?

Show answer

E

Pudendal neuralgia (entrapment between the sacrotuberous and sacrospinous ligaments or in the pudendal canal) causes burning perineal, genital or rectal pain that is worse sitting, with no objective sensory loss. It is associated with prolonged cycling. A diagnostic pudendal block helps confirm it.

Q5.

What forms the pudendal (Alcock) canal?

Show answer

B

The pudendal canal is a split in the obturator internus fascia on the lateral wall of the ischioanal fossa. The pudendal nerve runs in it with the internal pudendal vessels after re-entering through the lesser sciatic foramen.

Flashcards

See also