**Core Concept**
The adrenal glands are endocrine organs located on top of the kidneys, with each gland having a distinct venous drainage pattern. Understanding the venous drainage of the adrenal glands is crucial for various medical procedures, such as adrenal vein sampling.

**Why the Correct Answer is Right**
The right adrenal vein drains directly into the inferior vena cava (IVC), whereas the left adrenal vein drains into the left renal vein. This difference in venous drainage is due to the anatomic location of the right adrenal gland, which is situated closer to the IVC. The right adrenal vein is shorter and directly drains into the IVC, whereas the left adrenal vein is longer and drains into the left renal vein. This unique venous drainage pattern is essential for various medical procedures, including adrenal vein sampling and surgical interventions.

**Why Each Wrong Option is Incorrect**
**Option A:**
Incorrect because the right adrenal vein does not drain into the right renal vein. The right renal vein drains into the IVC, but it is not the destination of the right adrenal vein.

**Option B:**
Incorrect because the left adrenal vein drains into the left renal vein, not the right adrenal vein.

**Option C:**
Incorrect because the inferior phrenic veins drain into the brachiocephalic veins, not the right adrenal vein.

**Option D:**
Incorrect because the gonadal veins drain into the renal veins, not the right adrenal vein.

**Clinical Pearl / High-Yield Fact**
Remember that the right adrenal vein is shorter and directly drains into the IVC, whereas the left adrenal vein is longer and drains into the left renal vein. This knowledge is crucial for various medical procedures, including adrenal vein sampling and surgical interventions.

**Correct Answer: A. IVC**