What are the vertebral levels from which the pudendal nerve originates?

Pudendal Nerve Origin from Vertebral Levels

The pudendal nerve originates primarily from the ventral branches of sacral spinal roots S2-S4, with possible variations including contributions from S1 and/or S5 in some individuals. 1, 2

Anatomical Origin and Formation

• The pudendal nerve is formed by the ventral branches (anterior rami) of the sacral spinal roots S2-S4, making it a primarily sacral nerve 1
• In anatomical studies, the S2 root is the most consistent contributor, participating in pudendal nerve formation in approximately 85% of cases 3
• Variations in formation are common, with two main patterns observed:
  • Prefixed type (40% of cases): includes contributions from S1 and S2 roots 3, 4
  • Postfixed type: S3 root is dominant (66.7% of cases) or S4 root is more prominent (23.3% of cases) 3
• Some anatomical studies have documented rare contributions from S5 in approximately 5% of cases 2

Anatomical Course and Clinical Significance

• After formation from the sacral roots, the pudendal nerve typically forms from two cords:
  • Upper cord: continuation of the first root
  • Lower cord: fusion of second and third roots 2
• The nerve crosses posterior to the sacrospinous ligament (not over the ischial spine as sometimes incorrectly described) 2
• The pudendal nerve then enters the pudendal canal (Alcock's canal) where it divides into terminal branches 5
• Terminal branches include:
  • Inferior rectal nerve (typically arises within the pudendal canal in 90% of cases) 2
  • Perineal nerve
  • Dorsal nerve of penis/clitoris 3

Clinical Implications

• Understanding the exact vertebral origin of the pudendal nerve is critical for:
  • Accurate diagnosis of pudendal neuropathy 5
  • Proper administration of pudendal nerve blocks 3
  • Surgical approaches to decompress the nerve in pudendal canal syndrome 5, 2
• The pudendal nerve innervates:
  • Sensory: skin of perineum, genitalia (glans penis/clitoris), scrotum/labia majora, and perianal region 5
  • Motor: perineal muscles and external anal sphincter 5
  • Autonomic: contributes to sexual function including erection 5

Anatomical Variations and Surgical Considerations

• The inferior rectal nerve may have variable origin:
  • Most commonly arises within the pudendal canal (90% of cases) 2
  • Can arise before the pudendal canal in approximately 10% of cases, which may affect symptom presentation in pudendal canal syndrome 2
• The dorsal nerve of penis/clitoris shows variability:
  • May branch before entering the pudendal canal in 75% of cases 3
  • Can arise directly from S1 root in approximately 10% of cases 3
• These variations are important considerations during surgical procedures in the pelvic region to avoid iatrogenic nerve injury 1

Diagnostic Approaches

• MRI is the preferred imaging modality for evaluating the pudendal nerve and its origins 6
• Electrodiagnostic studies help confirm clinical diagnosis of pudendal neuropathy 6
• The Nantes criteria are used to diagnose pudendal neuralgia, which include:
  • Pain in the anatomical territory of the pudendal nerve
  • Pain worsened by sitting
  • Pain not waking the patient at night
  • No objective sensory loss on clinical examination
  • Positive response to pudendal nerve block 5