**Core Concept**
Pheochromocytomas are rare, catecholamine-secreting tumors that arise from the adrenal medulla. Episodic hypertension is a hallmark clinical feature of pheochromocytomas due to the excessive release of catecholamines, particularly epinephrine and norepinephrine.

**Why the Correct Answer is Right**
Pheochromocytomas lead to episodic hypertension due to the unregulated release of catecholamines. Catecholamines cause vasoconstriction, increased cardiac contractility, and increased heart rate, all of which contribute to elevated blood pressure. The episodic nature of catecholamine release is often associated with symptoms such as headaches, palpitations, and sweating. The excess catecholamines also stimulate the renin-angiotensin-aldosterone system, further contributing to hypertension.

**Why Each Wrong Option is Incorrect**
**Option A:** Carcinoid tumors, while secreting various hormones, are more commonly associated with flushing, diarrhea, and wheezing due to serotonin release, rather than episodic hypertension.

**Option B:** Insulinomas secrete excess insulin, leading to hypoglycemia, rather than causing episodic hypertension.

**Option D:** Zollinger-Ellison syndrome is characterized by excessive gastrin release, leading to peptic ulcers and diarrhea, but not episodic hypertension.

**Clinical Pearl / High-Yield Fact**
Remember that pheochromocytomas are catecholamine-secreting tumors, and their diagnosis often requires measurement of urinary or plasma metanephrines, as well as imaging studies to localize the tumor.

✓ Correct Answer: C. Pheochromocytoma