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Adrenal incidentalomas are defined as adrenal nodules that are discovered incidentally on abdominal imaging obtained for other reasons. Their incidence increases with age, being found on 1–7% (average 4%) of all CT or MRI scans. About 75% are nonfunctioning adrenal adenomas; however, 14% secrete increased cortisol or aldosterone, resulting in Cushing syndrome or aldosteronism, respectively, and 7% are pheochromocytomas. Another 4% of incidentalomas represented metastases or adrenal adenocarcinomas. The differential diagnosis for incidentally discovered adrenal masses also includes adrenal infection, hemorrhage, and cysts.

Autonomous cortisol secretion typically results in Cushing syndrome withlow or low-normal plasma ACTH and serum DHEAS. Patients should be further assessed with a 1 mg dexamethasone suppression test (DST). (See Cushing Syndrome for details.) On the DST, an 8 AM serum cortisol greater than or equal to 1.8 mcg/dL (50 nmol/L) indicates either Cushing syndrome or mild autonomous cortisol excess and a level greater than or equal to 3 mcg/dL (83 nmol/L) portends an increased mortality risk, even without clinical manifestations of Cushing syndrome).

Patients with hypertension are screened for primary aldosteronism with a PRA and serum aldosterone (see Primary Aldosteronism).

All patients with an adrenal incidentaloma should be screened for pheochromocytoma with plasma fractionated free metanephrines, except those whose nodules meet all the following criteria: (1) normotensive, (2) nodule density on unenhanced CT density 10 HU or less, (3) size 3 cm diameter or less, and (4) morphology not suspicious. (See Pheochromocytoma.)

Surgical resection is recommended in adrenal incidentalomas larger than 4 cm, unless it is an unmistakably benign myelolipoma, hemorrhage, or adrenal cyst. Smaller adrenal incidentalomas are usually observed after endocrine testing. Suspicion for malignancy in smaller adrenal incidentalomas is increased in patients under age 40 or and lesions that have suspicious features (heterogeneity or irregularity). A noncontrast CT should be performed to determine the density of the mass. Over 99% of adrenal pheochromocytomas and adrenocarcinomas have a density of 10 HU or more; patients with adrenal incidentalomas with densities of 10 HU or more that are not resected require both clinical follow-up and CT follow-up in 6–12 months.

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