An adrenal mass is a growth on one or both of your adrenal glands, the small hormone-producing organs that sit on top of each kidney. Most adrenal masses are discovered by accident during a CT scan or MRI ordered for an unrelated reason, which is why doctors often call them “incidentalomas.” In a large study of 25,000 generally healthy adults who received routine abdominal CT scans, about 1.4% had an adrenal mass they didn’t know about. The overwhelming majority of these growths are benign and never cause problems, but each one needs evaluation to rule out hormone overproduction or, rarely, cancer.
Why Most Are Found by Accident
Adrenal masses rarely announce themselves with symptoms. Most people learn they have one after getting imaging for back pain, kidney stones, abdominal issues, or a post-accident evaluation. The adrenal glands are small (roughly the size of a walnut), so even a growth of a centimeter or two can show up clearly on modern CT scanners without causing any physical discomfort. Because cross-sectional imaging has become so routine, these discoveries have become increasingly common.
Common Types of Adrenal Masses
The most common adrenal mass by far is a benign adenoma, a slow-growing, non-cancerous nodule made of normal adrenal tissue. Adenomas account for the vast majority of incidentally discovered adrenal growths. Other benign types include adrenal cysts (fluid-filled sacs) and myelolipomas (masses containing fat and bone marrow elements), both of which have a distinctive appearance on imaging and almost never require treatment.
On the more concerning end of the spectrum, adrenocortical carcinoma is a rare adrenal cancer with an incidence of roughly 0.7 to 2.0 cases per million people per year in the United States. It tends to occur in larger masses and carries a poor prognosis when it has spread, with a five-year survival rate below 15% for metastatic disease. In people who already have a known cancer elsewhere in the body, an adrenal mass may turn out to be a metastasis, a deposit of cancer that has spread from its original site. Distinguishing between a harmless adenoma and a metastasis in cancer patients is one of the most important tasks in adrenal imaging.
Functioning vs. Non-Functioning Masses
Some adrenal masses produce excess hormones, making them “functional.” Others appear hormonally silent and are classified as “non-functional.” This distinction matters because hormone overproduction can quietly damage your cardiovascular system and metabolism even before you notice symptoms.
About 10% of adrenal tumors secrete excess cortisol without producing the classic signs of Cushing syndrome (weight gain concentrated in the face and trunk, skin that bruises easily, muscle weakness). This condition, called subclinical hypercortisolism, can raise blood sugar and blood pressure over time. Interestingly, even masses classified as non-functional may secrete low levels of stress hormones that standard lab tests don’t pick up. Research using advanced hormone profiling has shown that people with supposedly silent adrenal tumors still produce higher levels of certain glucocorticoids compared to people without tumors, and this may contribute to a higher risk of diabetes and heart disease.
A less common but more dramatic type of functioning mass is a pheochromocytoma, a tumor that produces adrenaline and related hormones. The classic symptoms are episodes of severe high blood pressure, rapid heartbeat, headaches, and drenching sweats. These episodes can come and go unpredictably. An undiagnosed pheochromocytoma is dangerous because a sudden surge of hormones can trigger a hypertensive crisis, potentially leading to heart failure or circulatory collapse. This is why every adrenal mass needs hormonal screening before any procedure is done on it.
Some adrenal masses overproduce aldosterone, a hormone that regulates salt and water balance. Excess aldosterone causes high blood pressure that resists standard treatment, often paired with low potassium levels.
How Imaging Helps Identify the Mass
CT scanning is the primary tool for characterizing an adrenal mass, and one measurement in particular carries a lot of diagnostic weight: density, measured in Hounsfield units. A mass that measures less than 10 Hounsfield units on a non-contrast CT scan is almost certainly a benign, fat-rich adenoma. At that threshold, the specificity for a benign adenoma is 98 to 100%, meaning further workup is essentially unnecessary.
When a mass measures above 10 Hounsfield units, the picture is less clear. It could be a lipid-poor adenoma (a benign growth that simply doesn’t contain much fat) or something more concerning. In these cases, doctors use a contrast-enhanced CT with a “washout” study. The idea is straightforward: benign adenomas tend to release injected contrast dye quickly, while malignant masses hold onto it. An absolute washout above 60% and a relative washout above 40% are the traditional cutoffs suggesting a benign mass. However, these thresholds aren’t perfect. About 22% of malignant lesions in one large analysis showed washout patterns that mimicked benign adenomas, and more than a third of confirmed benign masses had washout values that looked suspicious. When the imaging remains uncertain, MRI or PET scanning may provide additional information.
Blood and Urine Tests for Hormone Activity
Every person found to have an adrenal mass should undergo basic hormonal screening, even if they feel perfectly fine. The standard workup typically covers three hormonal pathways.
- Cortisol: The initial screening test is an overnight dexamethasone suppression test. You take a small dose of a synthetic steroid at bedtime, then have your blood drawn the next morning. In a healthy person, the medication signals the adrenal glands to dial back cortisol production. If cortisol levels remain elevated, the mass may be producing cortisol on its own. This test is highly sensitive (95 to 100%) but can produce false positives, so abnormal results are confirmed with additional testing like late-night salivary cortisol or a 24-hour urine collection.
- Adrenaline-related hormones: Plasma free metanephrines (breakdown products of adrenaline) are measured to screen for pheochromocytoma. Because false positives are common, levels need to be two to three times the upper limit of normal to be considered diagnostic. This test is particularly important for any mass that doesn’t look like a straightforward adenoma on imaging.
- Aldosterone: If you have high blood pressure or unexplained low potassium, your doctor will check the ratio of aldosterone to renin in your blood. A ratio above a certain threshold triggers further confirmatory testing.
When Surgery Is Recommended
Size is one of the strongest predictors of whether an adrenal mass needs to come out. Most surgeons will recommend removal for any mass larger than 4 centimeters that also appears uneven in texture or dense on imaging (above 20 Hounsfield units), because adrenal cancer is more likely in larger, irregular-looking growths. Masses above 5 centimeters are generally removed regardless of how they look, with the exception of clearly benign cysts and myelolipomas, which have unmistakable imaging features.
Functional masses that produce excess hormones are typically removed as well, regardless of size, because the hormonal effects cause ongoing damage. For pheochromocytomas specifically, careful preparation before surgery is essential. Patients receive medications to block the effects of adrenaline for days to weeks before the operation, preventing a dangerous blood pressure spike during tumor removal.
Surgery is not recommended for small, stable, obviously benign masses that aren’t producing hormones. Removing these would expose you to surgical risk with no meaningful benefit.
What Follow-Up Looks Like
If your adrenal mass doesn’t require surgery, you’ll enter a monitoring period. Current guidelines recommend a follow-up imaging study at 3 to 6 months for masses with any suspicious features, or at 12 months for masses that appear clearly benign. The goal is to confirm the mass isn’t growing. Hormonal screening is typically repeated annually for up to four years, since some masses that appear non-functional at first can begin producing hormones over time.
After four years of stability, with no growth on imaging and normal hormonal results at each check, most patients can be discharged from routine surveillance. A mass that has remained unchanged for that long is very unlikely to cause problems going forward.