A 60-year-old man has a squamous cell carcinoma of the anal margin, below the dentate line. To which group of nodes does lymphatic drainage from this tumour site pass first?

• A Superior rectal nodes
• B Internal iliac nodes
• C Para-aortic nodes
• D Superficial inguinal nodes ✓

Explanation

Below the dentate line, lymph drains to the superficial inguinal nodes, then to the external iliac chain. Above the dentate line, drainage follows the superior rectal vessels to inferior mesenteric nodes and also to internal iliac nodes via the middle rectal vessels. This anatomical split explains why anal margin cancers present with groin nodal metastases while proximal anal canal cancers spread along mesorectal and pelvic routes first.

Reference: Gray's Anatomy for Students, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.