Pudendal nerve entrapment syndrome (PNES)

Introduction

Damage to the pudendal nerve can occur suddenly as a result of trauma to the pelvic region, prolonged bicycling, fractures or from falls.

Uncommon chronic pain, in which the pudendal nerve (located in the pelvis) is entrapped or compressed.

• Also known as Alcock canal syndrome

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Anatomy

Pudendal nerve:

• Origin: S2, S3, and S4 roots of ventral rami of sacral plexus
• Content: Sensory, motor, and autonomic fibers (however, injury causes sensory deficits more than motor)
• Course:
  • Courses between piriformis and coccygeus muscles
  • Departs pelvic cavity through greater sciatic foramen ventral to sacrotuberous ligament
  • Passes medial to and under sacrospinous ligament at ischial spine level to re-enter the pelvic cavity through lesser sciatic foramen
  • Courses in the pudendal canal “Alcock canal”
  • Terminal branches (three) end in ischioanal fossa:
    1. Inferior rectal branch
    2. Perineal branch
    3. Dorsal sensory nerve of the penis/clitoris

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Classification

Pudendal nerve compression based on anatomy:

The pudendal nerve entrapment syndromes subdivide into four types based on the level of compression.

• Type I – Entrapment below the piriformis muscle as the pudendal nerve exits the greater sciatic notch.
• Type II – Entrapment between sacrospinous and sacrotuberous ligaments is the most common cause of nerve entrapment.
• Type III – Entrapment in the Alcock canal.
• Type IV –  Entrapment of terminal branches.

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Aetiology

Mechanical causes:

• Pelvic surgery:
  • Pelvic organ prolapse (PoP) repair (M/C cause of pudendal neuralgia)
  • Mid-urethral sling surgery
  • Hysterectomy
  • Anterior colporrhaphy
• Direct trauma to buttocks/back
• Vaginal delivery
• Chronic constipation
• Excessive cycling: Chronic perineal microtrauma, which causes fibrosis in the pudendal canal and also the sacrospinous and sacrotuberous ligaments
• Prolonged sitting

Non-mechanical causes:

• Viral infections (herpes zoster, HIV)
• Multiple sclerosis
• Diabetes mellitus

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Clinical faetures

• Pain, numbness, and dysfunction in distribution of pudendal nerve (genitalia, rectum, and terminal urinary tract)
• Sexual dysfunction: Persistent arousal, dyspareunia, vulvodynia, and male impotence
• Sphincter dysfunction: Dyschezia, fecal incontinence, and urinary hesitancy
• Foreign body sensation in the anus, rectum, urethra, or vagina.

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Management

• Conservative management:
  • Avoidance of painful stimulus
  • Lifestyle modifications
• Physical therapy: Relaxation of pelvic floor muscles by releasing spasm and muscle lengthening
• Pharmacologic therapy: Analgesics, muscle relaxants, and anticonvulsants (including gabapentin and pregabalin)
• Pudendal nerve block: Local anesthetic/steroid infiltration
• Surgical decompression: Definitive treatment for PNE
  • Approaches: Transperineal, transgluteal, transischiorectal, and laparoscopy
• Neuromodulation: Latest treatment using a peripheral nerve stimulator, which causes stimulation of the pudendal nerve in the ischioanal fossa.
  • Pulsed radiofrequency: Newer neuromodulation technique and is considered safer than continuous radiofrequency ablation