**Core Concept**
Primary aldosteronism is a condition characterized by the excessive production of aldosterone, a mineralocorticoid hormone produced by the adrenal glands. This leads to sodium retention, potassium excretion, and subsequent hypertension accompanied by hypokalemia.

**Why the Correct Answer is Right**
Aldosterone stimulates the kidneys to retain sodium and water while promoting the excretion of potassium. The increased sodium levels lead to increased blood volume and blood pressure, resulting in hypertension. Additionally, the excessive potassium excretion leads to hypokalemia, which can cause muscle weakness, fatigue, and cardiac arrhythmias.

**Why Each Wrong Option is Incorrect**
* **Option A:** Renal artery stenosis can cause hypertension, but it is not typically associated with hypokalemia.
* **Option B:** Cushing's syndrome can cause hypertension, but it is usually associated with hyperkalemia due to the effects of cortisol on potassium levels.
* **Option C:** Pheochromocytoma can cause hypertension, but it is typically associated with hyperkalemia due to the effects of catecholamines on potassium levels.

**Clinical Pearl / High-Yield Fact**
Primary aldosteronism is often referred to as "Conn's syndrome" in honor of its discoverer, Jerome W. Conn. The condition is a common cause of secondary hypertension and can be diagnosed with the aldosterone-to-renin ratio (ARR) test.

**Correct Answer: C. Pheochromocytoma**