An Adrenal Nodule Found by Accident: How the Evidence Guides the Next Step

A benign, non-functioning adenoma is the answer for most people who learn they have an adrenal nodule found by chance, and the evidence-based workup exists to confirm that quickly while flagging the small number of nodules that are cancerous or hormone-producing. The 2023 guideline from the European Society of Endocrinology and European Network for the Study of Adrenal Tumors (ESE-ENSAT) reduces a potentially frightening finding to two clean questions: does the mass look benign on imaging, and does it secrete excess hormone. Non-contrast CT density answers the first. A short set of blood and urine tests answers the second. This guide walks through that reasoning.

Key points#

• An adrenal incidentaloma is a mass of one centimeter or larger found on a scan ordered for an unrelated reason.
• On non-contrast CT, a homogeneous mass of 10 Hounsfield units or less is treated as a benign fat-rich adenoma, regardless of size.
• Almost everyone gets a 1-mg overnight dexamethasone suppression test; a morning cortisol of 50 nmol/L (1.8 micrograms per deciliter) or less is a normal, suppressed result.
• A cortisol that does not suppress, without visible signs of Cushing syndrome, is labeled mild autonomous cortisol secretion (MACS).
• MACS links to cardiometabolic conditions such as type 2 diabetes, but whether removing the gland improves outcomes is not settled by trials.

Why these nodules turn up#

Cross-sectional imaging has become routine, so masses that were never suspected are now found often. When a CT of the abdomen is done for pain, a kidney stone, or trauma, the adrenal glands sit in the field of view, and a nodule occasionally appears. The great majority of these are benign, non-functioning adenomas that would never have caused symptoms.

That statistical reality sets the aim of the workup. The point is not to investigate everything exhaustively; it is to sort out the small fraction that are malignant or hormonally active while sparing everyone else from repeated scans, radiation, procedures, and worry. The 2023 ESE-ENSAT guideline is organized around exactly two risks: cancer, which imaging addresses, and hormone excess, which biochemistry addresses. Both assessments are done once at diagnosis for essentially every patient, and their results decide what happens next.

Reading the CT: density over diameter#

The most useful single number on your scan is the attenuation value on non-contrast CT, measured in Hounsfield units (HU). Adrenal adenomas, the most common benign adrenal tumor, tend to be rich in intracellular fat, and fat reads as radiologically dark. A homogeneous mass with an attenuation of 10 HU or less is fat-rich enough to be called a benign adenoma with high confidence.

The 2023 guideline makes a practical shift here. A homogeneous mass at 10 HU or less on non-contrast CT can be considered benign and needs no further imaging follow-up, whatever its size. That departs from older habits, which often set a size ceiling and scheduled repeat scans by default. As the review by Park and Kim summarizes these updates, density, not diameter, now carries the benign call.

Masses that fail to clear that bar earn more attention. Higher attenuation, uneven texture, irregular margins, and larger size all raise concern. Lesions of 4 centimeters or more, or those with indeterminate features, warrant multidisciplinary discussion, because the probability of adrenocortical carcinoma rises with size. Further imaging, such as delayed contrast washout studies or, in selected cases, functional imaging, is held in reserve for nodules that stay indeterminate after the first scan.

The hormone screen almost everyone receives#

Even a mass that looks benign can produce hormone in excess, so the guideline recommends a consistent core screen for essentially all incidentalomas.

Cortisol#

The first-line test is the 1-mg overnight dexamethasone suppression test (DST). You take 1 mg of dexamethasone late at night, and serum cortisol is measured the next morning. In a normally regulated gland, that signal shuts cortisol down. A morning cortisol of 50 nmol/L (1.8 micrograms per deciliter) or less is a normal, suppressed result and rules out autonomous cortisol secretion.

Catecholamines#

To screen for pheochromocytoma, a catecholamine-producing tumor, the guideline recommends plasma free metanephrines or urinary fractionated metanephrines, especially when the imaging features are not clearly those of a benign adenoma.

Aldosterone#

For patients with high blood pressure or unexplained low potassium, the aldosterone-to-renin ratio screens for primary aldosteronism, a treatable, aldosterone-driven cause of hypertension.

The gray zone: mild autonomous cortisol secretion#

The most interesting result is a dexamethasone test that does not fully suppress. When the post-dexamethasone cortisol sits above 50 nmol/L (1.8 micrograms per deciliter) in someone without overt physical signs of Cushing syndrome, the guideline calls this mild autonomous cortisol secretion, or MACS. The label is deliberately precise: the gland is producing cortisol partly outside normal control, but not enough to create the full syndrome.

A notable simplification in the 2023 guideline is that MACS is now defined by that single threshold, dropping the older subcategories that graded severity by how high the cortisol climbed. In practice, clinicians usually confirm with a repeat test rather than act on one borderline value, and they still weigh how far above the cutoff the number sits when deciding what to do.

Why does a mild finding get its own name? Because it is not metabolically neutral. As Park and Kim note, MACS is associated with a higher prevalence of conditions such as type 2 diabetes and dyslipidemia, while progression to overt Cushing syndrome is uncommon, on the order of less than one percent. The question sits at the intersection of endocrinology and metabolic epidemiology: a biochemical state is linked to cardiometabolic burden, yet randomized trials have not settled whether removing the gland improves outcomes compared with careful monitoring.

How the pieces drive a decision#

The guideline reads as a decision tree, not a verdict. A homogeneous mass at 10 HU or less with a normal hormone screen is benign and non-functioning, and generally needs no imaging follow-up. A mass that is large, indeterminate on imaging, or clearly hormone-producing moves toward multidisciplinary review and, for many, surgery. MACS occupies the middle ground. For a person with a one-sided adenoma, a cortisol that fails to suppress, and comorbidities plausibly tied to cortisol excess, the guideline supports discussing adrenalectomy, with the choice tailored to age, overall health, how persistently cortisol stays elevated, the severity of those comorbidities, and personal preference.

That tailoring is the honest reflection of the evidence. The imaging and biochemical thresholds are well defined and reproducible. Managing the milder findings still depends on judgment applied to you, one specific person, by your own clinicians.