Aldosteronoma or Conn syndrome, presents typically with

• diastolic hypertension
• metabolic alkalosis
• hypokalemia.

This entity is due to an autonomous solitary adrenal cortical adenoma in 80% of cases. Excess secretion of aldosterone can also occur in renin-related hypertension.

Primary hyperaldosteronism is distinguished from secondary hyperaldosteronism by measurement of serum renin; renin levels are low in the former and high in the latter. Clinically, Conn syndrome is characterized by hypertension, muscular weakness, paresthesias, headache, polyuria, and polydipsia. Edema is rare in these patients. Biochemical analysis may demonstrate hypokalemia, which may be the first clue to the diagnosis of aldosteronoma in a patient being evaluated for hypertension. The baseline plasma aldosterone is usually around 20 g/dL.

Most aldosteronomas are less than 2 cm in diameter and unilateral in 95% of cases. Assay of aldosterone levels in blood obtained via selective catheterization of both adrenal veins is the most reliable diagnostic procedure. Selective adrenal arteriography, adrenal phlebography, radionuclide studies and CT scans are helpful in diagnosis. Adrenal adenomas in this condition tend to be quite small, often 0.6-1.5 cm in diameter, and can be a challenge to detect, even by CT or MR imaging.

On CT, aldosteronomas are homogeneous and often hypodense, with an attenuation value near that of water. CT detects 70% of aldosteronomas, although small lesions may be missed. If CT findings are negative, selective adrenal venous sampling for aldosterone or a dexamethasone suppressed iodocholesterol adrenal scan may identify the lesion.

If a solitary adrenal mass is detected, surgical adrenalectomy will correct hypertension in 75% 90% of cases. Adrenal hyperplasia is the cause in most of the remaining 20% of cases of Conn syndrome, with adrenal carcinoma occurring rarely. Bilateral adrenalectomy in patients with hyperplasia is not usually an effective treatment and results in adrenal insufficiency.

In this patient, the aldosterone level was markedly elevated to >1200 and the potassium was below normal values, compatible with an aldosteronoma.