Conn syndrome results from overproduction of aldosterone from the zona glomerulosa of the adrenal cortex. Pheochromocytomas are catecholamine-producing neoplasms arising from the adrenal medulla.
The adrenal gland consists of the adrenal cortex and the adrenal medulla (Illustration A). The adrenal cortex has three zones. The outermost zone, the zona glomerulosa, produces aldosterone via stimulation by angiotensin II and potassium. The middle zone, the zona fasciculata, produces cortisol via ACTH stimulation. The innermost zone, the zona reticularis, produces androgens, also via ACTH stimulation. The adrenal medulla differs from the adrenal cortex in that it is derived from neural crest cells. The adrenal medulla releases catecholamines in response to sympathetic stimulation with acetylcholine.
Higgins and Fitzgerald describe a clinical approach in differentiating between adrenal gland disorders following incidental discovery of an adrenal mass. Determination of the size and functionality of the mass are key. Masses <6cm are usually benign. Functionality can be assessed via history, physical exam, and lab findings. Hypertension, hypokalemia, and hypernatremia are seen with hyperaldosteronism as in Conn syndrome. Episodic hypertension, headache, sweating, and tachycardia are seen with pheochromocytomas.
Pacak describes the role of the adrenal medulla in the pathophysiology of pheochromocytomas. The adrenal medulla is composed of chromaffin cells which release catecholamines - dopamine, norepinephrine, and epinephrine - in response to stimulation by preganglionic sympathetic neurons. These catecholamines modulate blood pressure, heart rate, and metabolism by binding to different classes of alpha and beta receptors. Epinephrine is largely responsible for tachyarrhythmias seen with pheochromocytomas, while norepinephrine is responsible for paroxysmal hypertension.
Illustration A shows the different areas of the adrenal gland and their respective secretory products.
Answers 1, 2, 4, & 5: The zona fasciculata produces cortisol and the zona reticularis produces androgens. These areas of the adrenal cortex are not involved in Conn syndrome. Pheochromocytomas arise from the adrenal medulla and do not involve the adrenal cortex.
Higgins JC, Fitzgerald JM. Evaluation of incidental renal and adrenal masses. Am Fam Physician. 2001 Jan 15;63(2):288-94, 299. PubMed PMID: 11201694.
PMID:11201694 (Link to Abstract)
Pacak K. Phaeochromocytoma: a catecholamine and oxidative stress disorder. Endocr Regul. 2011 Apr;45(2):65-90. PubMed PMID: 21615192; PubMed Central PMCID: PMC3414427.
PMID:21615192 (Link to Abstract)