**Core Concept**
Varicocele treatment involves testicular vein ligation to prevent retrograde blood flow and alleviate symptoms. The procedure targets the incompetent valves in the pampiniform plexus, a network of veins that drains the testis.

**Why the Correct Answer is Right**
The correct site for ligation is just below the internal spermatic vein junction, where the testicular vein enters the pampiniform plexus. This location is crucial because it allows for effective interruption of retrograde blood flow while preserving the testicular artery, which supplies oxygenated blood to the testis. The internal spermatic vein is a key structure in this procedure, as it is the site where incompetent valves lead to varicocele formation.

**Why Each Wrong Option is Incorrect**
**Option A:** Ligation at the level of the external spermatic vein is not effective in treating varicocele, as this structure is not directly involved in the pathophysiology of the condition.
**Option B:** Ligation at the level of the renal vein is not feasible or necessary for varicocele treatment, as the testicular vein does not enter the renal vein until it has already formed the pampiniform plexus.
**Option C:** Ligation at the level of the inguinal ligament is not anatomically correct, as the testicular vein does not pass through this region.

**Clinical Pearl / High-Yield Fact**
To remember the correct level for testicular vein ligation, recall that the procedure targets the junction between the testicular vein and the pampiniform plexus, just below the internal spermatic vein.

**Correct Answer:** C.