Anatomy Pelvis Head Neck · Year 1 · from Anatomy Pelvis Head Neck
Case 2: Pudendal Nerve Entrapment
Patient Demographics
- Age: 52 years old
- Sex: Female
- Occupation: Cyclist (recreational)
Chief Complaint
Chronic perineal pain and numbness that worsens with sitting for 18 months.
History of Present Illness
The patient developed insidious onset of burning pain and numbness in the perineal region approximately 18 months ago. The symptoms are localized to the area between the anus and clitoris. Pain is rated 6-7/10 at baseline and increases to 9/10 when sitting, particularly on hard surfaces. Interestingly, she reports significant relief when sitting on a toilet seat (which does not contact the perineum). Standing and lying down also provide relief. She is an avid cyclist and notes that symptoms began shortly after she increased her training for a long-distance cycling event. She has stopped cycling for 6 months without significant improvement. She denies urinary incontinence, fecal incontinence, or sexual dysfunction, though she reports dyspareunia. MRI of the lumbar spine and pelvis were unremarkable.
Physical Examination
- Vitals: Within normal limits
- Neurological examination:
- Sensory: Decreased sensation to light touch over the perineum in the distribution of the pudendal nerve (vulva, perineal body, perianal region)
- Motor: Normal anal sphincter tone, normal bulbocavernosus reflex
- Tinel's sign: Positive tenderness with percussion over the ischial spine on the right
- Pelvic examination: Tenderness on palpation of the right ischial spine region; no pelvic masses
Diagnostic Studies
- Pudendal nerve terminal motor latency testing: Prolonged latency on the right side consistent with nerve injury
- Diagnostic pudendal nerve block (CT-guided): Significant (>50%) pain relief following injection at the ischial spine
Diagnosis
Pudendal Nerve Entrapment (pudendal neuralgia), likely at the level of the ischial spine.
Anatomical Correlation
The pudendal nerve (S2-S4) is the principal somatic nerve of the perineum. It follows a distinctive course that creates multiple potential sites of entrapment. After forming in the pelvis, the nerve exits through the greater sciatic foramen below the piriformis muscle, curves around the posterior aspect of the ischial spine (where a pudendal nerve block is performed), and re-enters the perineum through the lesser sciatic foramen. It then travels in the pudendal canal (Alcock's canal), a fascial tunnel on the lateral wall of the ischioanal fossa formed by the obturator fascia. The nerve provides sensory innervation to the external genitalia and perineum, motor innervation to the external urethral and anal sphincters, and motor innervation to the perineal muscles. Entrapment can occur at the sacrospinous ligament (near the ischial spine), at the entrance to or within the pudendal canal, or from direct compression (as with cycling, where the pudendal nerve is compressed between the bicycle seat and the pubic bone). The diagnosis is supported by the "Nantes criteria": pain in the pudendal nerve distribution, worsened by sitting, no sensory impairment on waking, no objective sensory loss (though it may be present), and relief with pudendal nerve block.
Treatment
- Conservative management:
- Activity modification (avoid prolonged sitting, use cushion with cutout)
- Physical therapy focused on pelvic floor relaxation
- Medications: tricyclic antidepressants, gabapentinoids for neuropathic pain
- Interventional: Serial pudendal nerve blocks with local anesthetic and corticosteroid
- Surgical: Pudendal nerve decompression (release of sacrospinous ligament) if conservative measures fail