**Core Concept**
Conn's syndrome, also known as primary aldosteronism, is a condition characterized by excessive production of aldosterone, a hormone produced by the adrenal glands. This leads to hyperaldosteronism, causing hypertension, hypokalemia, and metabolic alkalosis. The underlying mechanism involves an overproduction of aldosterone, which is regulated by the renin-angiotensin-aldosterone system (RAAS).

**Why the Correct Answer is Right**
The most common cause of Conn's syndrome is a benign adrenal adenoma, accounting for approximately 70-80% of cases. These adenomas are usually unilateral and produce excessive amounts of aldosterone, leading to the characteristic symptoms. The aldosterone produced by these tumors acts on the collecting ducts of the kidneys, causing sodium retention and potassium excretion. This leads to hypertension, hypokalemia, and metabolic alkalosis.

**Why Each Wrong Option is Incorrect**
**Option A:** - This option is incorrect as it is not a common cause of Conn's syndrome. Other causes, such as familial hyperaldosteronism or idiopathic hyperaldosteronism, are much less common.
**Option B:** - This option is incorrect as it is not a direct cause of Conn's syndrome. While it may be associated with hypertension, it is not a primary cause of hyperaldosteronism.
**Option C:** - This option is incorrect as it is a rare cause of Conn's syndrome. Other causes, such as bilateral adrenal hyperplasia or familial hyperaldosteronism, are much less common.

**Clinical Pearl / High-Yield Fact**
A classic exam trap is to confuse Conn's syndrome with other causes of hypertension. Remember that Conn's syndrome is characterized by excessive aldosterone production, leading to hypertension, hypokalemia, and metabolic alkalosis. Always consider the RAAS pathway when evaluating patients with hypertension.

**Correct Answer: C. Bilateral adrenal hyperplasia.**