Clinical meaning
Pheochromocytoma is a catecholamine-secreting tumor arising from chromaffin cells of the adrenal medulla (90%) or extra-adrenal paraganglia (10%, called paragangliomas). These tumors produce excessive epinephrine, norepinephrine, and sometimes dopamine, causing episodic or sustained hypertension. Catecholamine excess activates alpha-1 adrenergic receptors (vasoconstriction, increased SVR), beta-1 receptors (increased heart rate, contractility, renin release), and beta-2 receptors (bronchodilation, glycogenolysis). The paroxysmal nature results from intermittent tumor catecholamine release triggered by physical activity, positional changes, abdominal palpation, or certain medications. Rule of 10s: 10% bilateral, 10% malignant, 10% extra-adrenal, 10% familial (associated with MEN 2A/2B, von Hippel-Lindau, neurofibromatosis type 1). Hypertensive crisis can be triggered by anesthesia induction, direct tumor manipulation, or medications that release stored catecholamines.
Exam relevance
Risk factors: - Multiple endocrine neoplasia type 2A and 2B (MEN syndrome) - Von Hippel-Lindau disease - Neurofibromatosis type 1 - Family history of pheochromocytoma - Succinate dehydrogenase gene mutations - Young patients with resistant hypertension