Pudendal nerve and internal pudendal vessels

Pudendal Nerve - The Perineal Powerhouse

• Origin: Ventral rami of S2-S4.
• Function: Main sensory and motor nerve of the perineum.
  • Motor: Innervates the external urethral sphincter and external anal sphincter.
  • Sensory: Innervates the penis, clitoris, posterior scrotum/labia, and perineal skin.
• 📌 Mnemonic: S2, S3, S4 keeps the penis off the floor.

⭐ The pudendal nerve exits the pelvis via the greater sciatic foramen, crosses the sacrospinous ligament, and re-enters the perineum through the lesser sciatic foramen.

Internal Pudendal Vessels - Pelvic Plumbing Partners

• Internal Pudendal Artery & Vein: The primary blood supply and drainage for the perineum. They travel in lockstep with the pudendal nerve.

• Path:

  • Originate from the internal iliac artery & vein.
  • Exit pelvis via greater sciatic foramen.
  • Cross ischial spine & re-enter perineum via lesser sciatic foramen.
  • Course through the pudendal canal (Alcock's canal).

• Key Branches:

  • Inferior rectal artery: lower anal canal.
  • Perineal artery: perineal muscles.
  • Arteries of penis/clitoris (dorsal, deep).

⭐ The internal pudendal artery is a branch of the anterior division of the internal iliac artery and is the principal blood supply to the perineum.

Pudendal Canal (Alcock's) - The Tight Squeeze

and its contents: pudendal nerve, artery, and vein)

• A fascial tunnel formed by the splitting of the obturator internus fascia.
• Located on the lateral wall of the ischioanal fossa, providing a protected pathway.
• Contents: Transmits the internal pudendal artery, internal pudendal vein(s), and the pudendal nerve to the perineum.

⭐ Pudendal nerve entrapment within Alcock's canal, often seen in cyclists, leads to perineal pain and numbness due to compression of the neurovascular bundle.

Clinical Applications - Blocks, Aches & Pains

• Pudendal Nerve Block
  • Indications: Anesthesia for childbirth (second stage), episiotomy repair, and other minor perineal procedures.
  • Landmark: The ischial spine is palpated to guide the injection.
  • Approaches:
    • Transvaginal: Needle guided through the vaginal wall to the ischial spine.
    • Perineal: Needle inserted near the ischial tuberosity.

⭐ The ischial spine is the key palpable landmark for administering a pudendal nerve block, as the nerve passes just medial and inferior to it.

• Pudendal Neuralgia (Alcock's Canal Syndrome)
  • Cause: Compression or entrapment of the nerve, often within Alcock's canal.
  • Symptoms: Chronic burning pain, numbness, or tingling in the perineum. Pain is characteristically worse with sitting and relieved by standing or lying down.

High‑Yield Points - ⚡ Biggest Takeaways

• The pudendal nerve originates from S2-S4 roots, providing key perineal innervation.
• It exits the pelvis via the greater sciatic foramen, loops around the ischial spine, and re-enters via the lesser sciatic foramen.
• The internal pudendal artery and vein travel alongside the nerve.
• It courses through the pudendal canal (Alcock's canal) to reach the perineum.
• Provides motor function to the external urethral/anal sphincters and sensory innervation to the external genitalia.
• A pudendal nerve block targets the nerve at the ischial spine for perineal anesthesia.