The most appropriate treatment for this patient is spironolactone. He has primary hyperaldosteronism (PA) due to a bilateral adrenal source as evidenced by the lack of lateralization on adrenal vein sampling (AVS). Bilateral adrenal hyperplasia is the most common etiology of PA, accounting for approximately 60% of cases, and spironolactone is the treatment of choice. Spironolactone is a mineralocorticoid receptor (MR) antagonist that can improve blood pressure, normalize serum potassium concentration, and reduce excess cardiovascular risk related to hyperaldosteronism. Eplerenone is an alternative MR antagonist that is less likely to cause gynecomastia in men because of greater MR selectivity; however, use of eplerenone for this indication is off-label. Antagonists of the aldosterone-sensitive sodium channel (amiloride) can be used as second-line therapy.

Bilateral adrenalectomy is not appropriate for the routine management of PA, as this would risk primary adrenal failure, thus necessitating life-long glucocorticoid and mineralocorticoid therapy.

Dexamethasone, a long-acting synthetic glucocorticoid, has a role in treating only a small percentage of patients who have glucocorticoid-remedial hypertension, a very rare autosomal dominant condition resulting from ectopic expression of aldosterone synthase in the cortisol-producing zona fasciculata. Administration of dexamethasone will suppress pituitary adrenocorticotropic hormone (ACTH) secretion in these patients and therefore mineralocorticoid production. However, hyperaldosteronism in most patients is independent of ACTH secretion, and suppression with exogenous glucocorticoid is not an effective therapy.

Left adrenalectomy should not be performed because the patient has a bilateral cause of PA. The left adrenal adenoma detected by CT scan is an incidental finding and is likely not the cause of this patient's hyperaldosteronism. Because nonsecreting adrenal adenomas are common, AVS is needed in most patients with hyperaldosteronism to determine the source of aldosterone secretion when imaging studies show an adrenal adenoma to assess its contribution to excess mineralocorticoid production. AVS should be done at a high-volume referral center due to a high risk of complications when significant procedural experience is lacking.