Aldosteronoma

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's syndrome is characterized by hypertension, muscular weakness, paresthesias, headache, polyuria, and polydipsia. Oedema is rare in these patients. Biochemical analysis may demonstrate hypokalaemia, which may be the first clue to the diagnosis of aldosteronoma in a patient being evaluated for hypertension. The baseline plasma aldosterone is usually greater than 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 (Fig.1). On MRI, aldosteronomas are generally hypointense on T1-weighted images and slightly hyperintense on T2-weighted images. 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's syndrome, with adrenal carcinoma occurring rarely. Bilateral adrenalectomy in patients with hyperplasia is not usually an effective treatment and results in adrenal insufficiency.

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