The adrenal glands are located on top of the kidneys and secrete hormones that regulate metabolism, salt and water balance, and stress responses. Most adrenal masses are found incidentally on autopsy and are benign, but a small number can be malignant. When adrenal masses are discovered incidentally during diagnostic studies for other clinical conditions, they are commonly termed “incidentalomas.”When an adrenal mass is discovered, management depends on determining whether the lesion is nonfunctioning or hormonally active and whether it is benign or malignant. Grumbach and associates reported on a National Institutes of Health conference on the management of clinically inapparent adrenal masses.
Expert opinion, scientific evidence, and public discussion by members of the panel were used to develop a management guideline. The prevalence of clinically inapparent adrenal masses detected at autopsy is less than 1 percent in patients younger than 30 years and is 7 percent in patients 70 years or older. Most causes of adrenal masses are benign. Clinically important factors that increase the likelihood of malignancy include a history of cancer and larger size of the mass (there is an increasing likelihood of cancer when the mass is greater than 4 cm in size).
Most adrenal masses are nonfunctioning tumors, although some patients have subclinical hypercortisolism (also known as subclinical Cushing's syndrome). Over time, nonfunctioning adrenal masses may increase in size by at least 1 cm. The threshold at which increasing mass size becomes clinically significant is unknown.
Evaluation of the patient with a clinically inapparent adrenal mass revealed by an imaging study includes a complete history and physical examination, biochemical evaluation for hormone excess and, possibly, further radiologic imaging studies. An overnight dexamethasone suppression test is useful to detect subclinical hypercortisolism, an entity of unknown clinical significance. A plasma free-metanephrine determination can detect or rule out pheochromocytoma. If the patient has hypertension, a serum potassium level and a plasma aldosterone concentration–plasma renin activity ratio can identify primary aldosteronism.
Imaging studies can be helpful in differentiating benign from malignant lesions. On computed tomography, almost all lesions smaller than 4 cm with smooth borders are benign. Lesions between 4 and 6 cm that are hormonally inactive can be monitored. In contrast, lesions greater than 6 cm in size are more likely to be malignant, and surgery should be considered. Fine-needle aspiration may be useful in equivocal situations, but only after pheochromocytoma has been excluded.
If signs and symptoms of glucocorticoid, mineralocorticoid, adrenal sex hormone, or catecholamine excess are present, surgery is usually indicated. However, medical therapy might be possible in certain patients, such as patients with Cushing's syndrome who are poor surgical candidates and patients with aldosterone-secreting tumors. When clinical signs are not present but there is biochemical evidence of adrenal hyperactivity, adrenalectomy should be considered on an individual basis, depending on future risk and comorbid conditions such as hypertension.
If an incidentaloma is nonfunctioning, variables that affect management include the size, imaging characteristics, and growth rate of the lesion. Excision is generally recommended for lesions greater than 6 cm in size, lesions with imaging characteristics indicative of malignancy, and lesions with a rapid growth rate. Follow-up for patients with adrenal incidentalomas includes monitoring tumor size by computed tomography and repeat hormonal evaluation. Resection of an adrenal mass may be done by open or laparoscopic adrenalectomy.
The authors conclude that although more information is needed about the natural history and evaluation of clinically inapparent adrenal masses, most are benign and do not require intense long-term clinical follow-up (see accompanying table).