Which statement about lymphatic drainage of the anal canal is correct?
- A The entire anal canal drains to the superficial inguinal nodes
- B Below the dentate line, drainage is to the para-aortic nodes
- C Above the dentate line, drainage is to the inferior mesenteric and internal iliac nodes ✓
- D The dentate line has no relevance to lymphatic spread of anal tumours
Correct answer: C. Above the dentate line, drainage is to the inferior mesenteric and internal iliac nodes
Explanation
The dentate line divides the anal canal into two distinct lymphatic territories. Above it, lymph follows the superior rectal vessels to the inferior mesenteric chain and also drains to internal iliac nodes via middle rectal channels. Below the dentate line, drainage is to the superficial inguinal nodes, which is why low anal margin cancers can produce inguinal metastases while upper canal tumours do not.
Reference: Gray's Anatomy for Students, 4th ed.
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