Which of the following BEST distinguishes internal from external haemorrhoids anatomically?

• A Internal haemorrhoids are covered by squamous epithelium; external by columnar
• B External haemorrhoids are always painless unless thrombosed
• C Internal haemorrhoids always prolapse; external haemorrhoids never prolapse
• D Internal haemorrhoids arise above the dentate line and are covered by insensate columnar/transitional mucosa ✓

Explanation

Internal haemorrhoids arise above the dentate line from the internal haemorrhoidal plexus and are covered by columnar or transitional (insensate) epithelium — hence they are painless unless strangulated. External haemorrhoids arise below the dentate line from the external haemorrhoidal plexus and are covered by pain-sensitive squamous epithelium — thrombosed external haemorrhoids are acutely painful. This anatomical distinction underlies their clinical presentation.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.