The most appropriate next step in management is to evaluate for pheochromocytoma, preferably by measurement of plasma free metanephrines in this patient. Approximately 10% to 15% of incidentally discovered adrenal masses are functional, although most have no overt clinical manifestations. Therefore, all patients with an incidentally noted adrenal mass should be evaluated for the autonomous secretion of cortisol and catecholamines, and those with hypertension should also undergo testing for primary hyperaldosteronism. The low-dose dexamethasone suppression test should be performed to evaluate for subclinical Cushing syndrome given its superior sensitivity compared with other screening tests (24-hour urine free cortisol and late-night salivary cortisol); this test was negative in this patient. Measurement of 24-hour urine metanephrines and catecholamines is the usual first test in most asymptomatic patients to evaluate for catecholamine hypersecretion, although in those with imaging suggestive of pheochromocytoma, measurement of plasma free metanephrines is the preferred study because of its very high sensitivity and high negative predictive value for a normal study. Imaging in this patient reveals a well-circumscribed partially cystic lesion with high attenuation on noncontrast CT scan, which is in keeping with a pheochromocytoma and is not typical of an adrenocortical adenoma, which characteristically has low attenuation on CT scan (density <10 Hounsfield units) due to relatively high lipid content.

Management of an adrenal incidentaloma depends on its size, imaging characteristics (phenotype), and hormonal functioning. Almost all adrenal tumors that are overtly functional are larger than 6 cm in size or have unfavorable imaging characteristics should be considered for surgical removal. However, biopsy or surgical resection of any adrenal mass prior to ruling out a pheochromocytoma is not recommended, as any manipulation of a catecholamine-secreting tumor without appropriate preoperative management can precipitate a hypertensive crisis.

Measurement of the plasma aldosterone to plasma renin ratio is indicated as part of the evaluation of an incidentally discovered adrenal mass in a patient with hypertension, but not in this individual who has normal blood pressure.

Not performing additional testing may miss a subclinical pheochromocytoma and would therefore not be an appropriate next step in management.