Pheochromocytoma is most commonly caused by tumors in which gland?

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Pheochromocytoma originates from chromaffin cells in the adrenal medulla, the inner part of the adrenal gland that acts as a neuroendocrine tissue. These cells produce catecholamines—epinephrine and norepinephrine—that cause the classic episodic hypertension, headaches, sweating, and tachycardia. Although tumors can occasionally arise outside the adrenal gland along the sympathetic chain (paragangliomas), the adrenal medulla is by far the most common site. The other options involve tissues that produce different hormones (the cortex makes corticosteroids; the pituitary and thyroid secrete other endocrine products) and are not typical sources of pheochromocytoma.