An adult presents with an exquisitely tender, throbbing swelling at the anal verge with marked skin induration, diagnosed as a perianal abscess extending below the pectinate (dentate) line. Which nerve mediates the severe pain?
- A Inferior rectal nerve, a branch of the pudendal nerve carrying somatic afferents ✓
- B Sympathetic fibres of the inferior mesenteric plexus
- C Pelvic splanchnic nerves (S2 to S4) via visceral afferents
- D Perforating cutaneous branches of S2 to S4 via the coccygeal plexus
Correct answer: A. Inferior rectal nerve, a branch of the pudendal nerve carrying somatic afferents
Explanation
Below the pectinate line the anal canal is ectodermal in origin and receives somatic innervation from the inferior rectal nerve, a branch of the pudendal nerve (S2, S3, S4). Somatic afferents explain the sharp, well localised, exquisite pain typical of perianal lesions. Mucosa above the pectinate line is viscerally innervated and relatively painless, so visceral pathways in options C and B do not account for this presentation.
Reference: Bailey and Love Short Practice of Surgery, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.