A 55-year-old man has an anal fissure causing severe pain on defecation. A biopsy taken from a lesion just distal to the pectinate (dentate) line shows squamous carcinoma. Which nerve provides the somatic sensory supply responsible for his severe pain?

• A Perforating cutaneous nerve of S2 and S3
• B Visceral afferents travelling with the pelvic splanchnic nerves
• C Inferior rectal branch of the pudendal nerve ✓
• D Sympathetic fibres from the hypogastric plexus

Explanation

Below the pectinate line the anal canal is ectodermal in origin and is supplied somatically by the inferior rectal nerve, a branch of the pudendal nerve, so lesions here are exquisitely painful. Above the line, visceral afferents travel with autonomic nerves and lesions such as internal haemorrhoids are typically painless, which is exactly why option B fails for this patient.

Reference: Last's Anatomy: Regional and Applied, 12th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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