## Why option 1 is correct The superficial inguinal lymph nodes (marked **A**) form the horizontal group along the inguinal ligament and receive direct lymphatic drainage from the vulva, perineum, lower abdominal wall (below umbilicus), and lower limb skin. This makes them the sentinel lymph node group for vulvar squamous cell carcinoma. According to Gray's Anatomy 42e Ch 80, vulvar and scrotal skin cancers metastasize to the superficial inguinal nodes first, and sentinel lymph node biopsy of this group guides nodal staging and prognosis in vulvar cancer management. ## Why each distractor is wrong - **Option 2**: While deep inguinal nodes (C) do exist along the femoral vein, they are NOT the primary drainage site for vulvar skin. Deep inguinal nodes receive drainage from the glans penis specifically (not shaft skin) and are involved in metastasis only after superficial node involvement. The vulva drains directly to superficial nodes. - **Option 3**: The Cloquet node (D), the highest deep inguinal node located in the femoral canal medial to the femoral vein, is not the sentinel node for vulvar cancer. It may be involved in advanced disease but is not the first-line drainage site. It is more relevant for melanoma and advanced vulvar cancer requiring complete groin dissection. - **Option 4**: Axillary nodes receive lymphatic drainage from the abdominal wall ABOVE the umbilicus, not below. The vulva is below the umbilicus and therefore drains to inguinal nodes, not axillary nodes. This represents a common anatomical error in understanding the watershed of abdominal wall drainage. **High-Yield:** Vulvar/scrotal/penile skin cancers → superficial inguinal nodes (sentinel site); glans penis → deep inguinal nodes (skip superficial); above umbilicus → axillary nodes; below pectinate line → superficial inguinal nodes. [cite: Gray's Anatomy 42e Ch 80]
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