Primary aldosteronism: a pictorial essay

Primary aldosteronism is defined as secondary hypertension accompanied by aldosterone hypersecretion that leads to suppressed plasma renin, hypokaremia and hypertension. Primary aldosteronism occurs in 3–15% of hypertensive patients and is commonly caused by aldosterone-producing adenoma (APA) or bilateral idiopathic hyperaldosteronism (IHA). APA is usually treated by adrenalectomy, whereas IHA is best managed medically. Therefore, it is important to distinguish between unilateral and bilateral disease. Computed tomography (CT) is used to differentiate the subtypes. Even when multidetector CT is used, the detection rate of APAs of 1 cm or less is lower than 60% for the following reasons: (a) aldosterone secretion does not depend on tumor size, (b) a tumor may exist without lipid-rich cells, and (c) non-functioning unilateral adenomas are not uncommon, especially in older patients. Adrenal venous sampling is the gold standard for the differentiation of unilateral from bilateral disease in patients with primary aldosteronism. It is important to compare the laterality of aldosterone secretion by performing simultaneous bilateral blood collection 15 min following adrenocorticotropic hormone stimulation. The value of (aldosterone/cortisol)side/(aldosterone/cortisol)contralateral side provides the best discrimination between patients with and without APA.