An adrenal incidentaloma is a mass found on one of your adrenal glands during imaging that was done for a completely unrelated reason. You go in for a CT scan after a car accident, a kidney stone workup, or routine abdominal imaging, and a growth shows up on your adrenal gland that nobody was looking for. These are remarkably common, showing up in roughly 0.5% to 4.2% of people who get abdominal imaging, and in about 2.3% of people examined in autopsy studies. The vast majority are benign and never cause problems, but every one needs a basic evaluation to rule out two things: hormone overproduction and cancer.
Why Most Are Harmless
The most common type of adrenal incidentaloma is a nonfunctioning adenoma, a small, benign growth that produces no excess hormones and poses no cancer risk. These make up the majority of cases. They sit quietly on the adrenal gland, often for a person’s entire life, without causing symptoms or health consequences.
That said, a meaningful minority of incidentalomas do turn out to be something that needs attention. Roughly 5% to 6.5% are pheochromocytomas, tumors that can release surges of adrenaline and related hormones. About 8% of those pheochromocytomas are completely silent, causing no symptoms at all, which is exactly why screening matters even when you feel fine. A smaller percentage produce excess cortisol or aldosterone. And in rare cases, particularly with larger masses, the growth can be an adrenal cancer.
The Hormone Workup
Every adrenal incidentaloma requires blood and urine tests to check whether it’s producing hormones. The two tests considered mandatory are a measurement of metanephrines (to rule out pheochromocytoma) and an overnight dexamethasone suppression test (to check for excess cortisol production). For the cortisol test, you take a low dose of a steroid pill at bedtime, then have your blood drawn the next morning. If your cortisol level stays above 1.8 micrograms per deciliter, that suggests the adrenal gland is producing cortisol on its own, a condition called mild autonomous cortisol secretion, or MACS. This isn’t full-blown Cushing’s syndrome with obvious symptoms like a round face and stretch marks. It’s a subtler pattern of excess cortisol that can quietly contribute to weight gain, high blood sugar, bone thinning, and high blood pressure over time.
If you have high blood pressure, with or without low potassium, your doctor will also check your aldosterone-to-renin ratio to screen for primary aldosteronism. This is a condition where the adrenal gland overproduces aldosterone, a hormone that regulates salt and water balance, driving blood pressure up. It’s one of the most common treatable causes of hypertension, and an adrenal mass in someone with hard-to-control blood pressure raises suspicion.
How Imaging Determines the Risk
The single most useful piece of information from a CT scan is the density of the mass, measured in Hounsfield units (HU). Benign adenomas are typically rich in fat, which makes them appear less dense on an unenhanced (no contrast dye) scan. For over two decades, the standard cutoff has been 10 HU or less: a mass at or below that density is almost certainly a benign, fat-rich adenoma regardless of its size. More recent evidence suggests that for masses smaller than 4 centimeters, a threshold of 20 HU may be safe enough to rule out malignancy, though the traditional 10 HU cutoff remains the most widely used benchmark in clinical guidelines.
When a mass measures above 10 HU on an unenhanced scan, it’s considered “lipid-poor,” and additional imaging steps are needed. One common approach has been a contrast washout study, where dye is injected and the scan is repeated after a delay. Benign adenomas tend to release the contrast dye quickly, with a relative washout greater than 50%. Malignant tumors hold onto the dye, typically showing a relative washout below 40%. Size matters too. The risk of malignancy rises significantly once a mass exceeds 4 centimeters.
When Surgery Is Recommended
Surgery is recommended in three main scenarios. First, any mass that’s actively producing excess hormones (a functioning tumor) generally needs to come out, since the hormonal effects carry long-term health risks. Second, any mass larger than 4 centimeters that lacks clearly benign imaging features should be removed, because the cancer risk climbs with size. Third, any mass with suspicious radiological characteristics, such as irregular borders, high density, or slow contrast washout, warrants surgical removal regardless of size.
There’s some debate around the exact size threshold. Different expert groups have proposed cutoffs ranging from 4 to 6 centimeters. But the prevailing view is that 4 centimeters is the point at which a mass that doesn’t look clearly benign on imaging should be taken out. A 5-centimeter mass that measures below 10 HU on an unenhanced CT, for example, has a cancer risk close to zero, so size alone doesn’t automatically mean surgery. Context matters.
When surgery is needed, it’s almost always done laparoscopically, through small incisions, with most people going home within a day or two and returning to normal activity within a few weeks.
What Follow-Up Looks Like
If your mass is small, measures below the density thresholds for concern, and your hormone tests come back normal, you may not need any further imaging at all. Current guidelines have moved away from the older approach of scanning every patient repeatedly over years.
For masses that are indeterminate but not concerning enough for surgery, follow-up imaging is typically done at 6 to 12 months. If the growth has expanded by more than 20% in diameter (and at least 5 millimeters), surgery becomes the next step. In a 10-year follow-up study of nonfunctioning adrenal incidentalomas, significant growth of 10 millimeters or more occurred in about 8.9% of patients, though shorter studies have reported rates as low as 1.2%. The risk of meaningful growth is higher in people who are overweight or obese.
As for repeat hormone testing, the current approach is simpler than it used to be. If your initial biochemical workup is completely normal, routine retesting is no longer recommended unless you develop new symptoms or worsening health problems like uncontrolled blood sugar or blood pressure. The old practice of annual hormonal screening for every patient has largely been dropped.
Living With an Adrenal Incidentaloma
For most people, the diagnosis is far more alarming than the actual condition. Finding an unexpected mass on an organ you may not have thought much about naturally triggers anxiety. But the reality is that the overwhelming majority of adrenal incidentalomas are benign growths that will never affect your health. The workup exists to catch the small fraction that do matter, and once that evaluation is complete and comes back reassuring, many people require nothing more than a single follow-up scan or no additional monitoring at all.
The most important thing is completing that initial evaluation fully: the hormone tests and the imaging characterization. Skipping the workup because you feel fine is the real risk, since conditions like pheochromocytoma or mild autonomous cortisol secretion can cause damage silently over years. Once you have clear answers, the path forward is usually straightforward.