Curriculum · Metabolic and Endocrine and Diabetes Mellitus
Approach to an adrenal lesion
What it is
An adrenal incidentaloma is an adrenal mass of 1 cm or more found incidentally on imaging performed for reasons other than suspected adrenal disease. Prevalence is 3-7 % in adults and rises with age, above 10 % after 70 years. Most are benign, non-functional adenomas. It still matters, because malignancy and hormonal hypersecretion must be excluded even when the patient is asymptomatic. The lesions fall into four categories. Benign and non-functional is the lipid-rich adrenal adenoma, the most common one, homogeneous and with a low HU on CT, under 10 HU. Functional but benign covers the cortisol-secreting adenoma, the aldosteronoma and pheochromocytoma, all of which need biochemical confirmation. Malignant covers adrenocortical carcinoma and metastasis, which are irregular and heterogeneous, over 4 cm, with HU above 20 and delayed washout. The others are myelolipoma, cyst and hemorrhage; myelolipoma holds macroscopic fat and cysts are of water density.
How it is diagnosed
Two questions are asked. First, is the lesion functional: does it secrete any hormones? That is answered by a check of symptoms and hormonal levels. Second, is there suspicion for malignancy on imaging: contrast pattern, borders, size change, calcifications and distant metastases. Three functional lesions are worth naming. Primary aldosteronism gives easily provoked hypokalemia, slight hypernatremia and hypertension with an adrenal incidentaloma; the findings are a high plasma aldosterone concentration (at or above 10 ng/dL), a low plasma renin activity (below 1.0 ng/mL hour) and a raised aldosterone-to-renin ratio on a morning blood sample. It is not necessary to stop a patient's antihypertensive medications prior to testing for primary hyperaldosteronism. Pheochromocytoma gives paroxysmal elevated blood pressure with tachycardia, pounding headaches, palpitations and diaphoresis, again with an adrenal incidentaloma; the screening test is biochemical first, by 24-hour urine total metanephrines and catecholamines or by plasma free metanephrines and free normetanephrines, and not by urinary VMA. Cushing syndrome gives central obesity, facial plethora, proximal muscle weakness, abdominal striae, ecchymosis and amenorrhea or erectile dysfunction, with a raised serum cortisol following a low-dose dexamethasone test. A worked example: a 27-year-old male referred for refractory HTN with a newly identified lesion on the adrenal gland and an unremarkable bedside examination, whose labs showed hypernatremia, hypokalemia and elevated 24-hour urine aldosterone. Serum K is low, aldosterone high, plasma renin low, and serum Na mildly elevated or normal; the ABG shows metabolic alkalosis, since potassium loss in the collecting ducts leads to H+ secretion and H+ loss. The lesion is then confirmed with abdominal CT or MRI. The differential for hypertension with hypokalemia also holds renovascular HTN from renal artery stenosis, renin secreting tumors, CAH and Cushing's. An adrenal lesion is rarely biopsied because it is highly vascular, so the histopathological diagnosis is usually established only after surgical resection.