Question

A known case of anal carcinoma with mass near the anal opening comes for follow-up. Which of the following lymph nodes are most likely involved?

• A. Superficial inguinal lymph nodes
• B. Deep inguinal lymph nodes
• C. External iliac lymph nodes
• D. Internal iliac lymph nodes

Hint:

Anal canal below pectinate line and perianal region drain to superficial inguinal lymph nodes.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The lymphatic drainage of the anal canal is divided by the Dentate (Pectinate) Line. The question specifies a mass "near the anal opening," which refers to the distal anal canal or anal margin.
Step 2: Detailed Explanation:

Anatomical Drainage:
1. Above the Dentate Line: The lymphatics follow the superior rectal vessels to the internal iliac and para-aortic nodes.
2. Below the Dentate Line: The lymphatics drain downward and laterally to the superficial inguinal lymph nodes.

Clinical Significance: Squamous cell carcinoma (SCC) is the most common type of cancer in the anal canal below the dentate line. During physical examination and follow-up, it is vital to palpate the groin for enlarged, firm superficial inguinal nodes, as this is the primary site of regional spread.

Treatment Impact: If inguinal nodes are positive, they must be included in the radiation field during primary treatment (Nigro protocol: Chemoradiotherapy).

Differentials: Rectal cancer (above the rectum) drains to the inferior mesenteric nodes. Cancers of the mid-anal canal may show mixed drainage to both iliac and inguinal systems.

Step 3: Final Answer:
Cancers of the anal canal located below the pectinate line characteristically drain to the superficial inguinal lymph nodes.