Why are internal haemorrhoids typically painless while a thrombosed external haemorrhoid causes severe pain?
- A Internal haemorrhoids arise above the dentate line, lined by mucosa innervated by visceral autonomic nerves insensitive to sharp pain ✓
- B Internal haemorrhoids have a lower intravascular pressure than external ones
- C External haemorrhoids are larger and stretch the sphincter muscles
- D Internal haemorrhoids are covered by skin supplied by inferior rectal nerves
Correct answer: A. Internal haemorrhoids arise above the dentate line, lined by mucosa innervated by visceral autonomic nerves insensitive to sharp pain
Explanation
The dentate line marks the embryological junction between endoderm and ectoderm. Above it the anal canal is lined by columnar epithelium with visceral autonomic innervation, which transmits stretch but not sharp pain, so internal haemorrhoids bleed painlessly. Below the dentate line the canal is lined by stratified squamous epithelium with somatic innervation via the inferior rectal branch of the pudendal nerve, making thrombosed external haemorrhoids exquisitely painful.
Reference: Bailey and Love's Short Practice of Surgery, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.