An adrenal adenoma is a benign (noncancerous) tumor that grows on the outer layer of one of your adrenal glands, the small hormone-producing organs that sit on top of each kidney. These growths are common, showing up in roughly 2% of healthy adults, and the vast majority never cause symptoms or require treatment. Most people discover they have one only because a CT scan or MRI was done for an unrelated reason, which is why doctors often call them “adrenal incidentalomas.”
Why Most Adenomas Don’t Cause Problems
Adrenal adenomas fall into two categories: functioning and nonfunctioning. A nonfunctioning adenoma doesn’t produce excess hormones. It simply sits on the adrenal gland without disrupting anything. Most adrenal adenomas are nonfunctioning, and if they’re small, they don’t need treatment at all.
A functioning adenoma, on the other hand, pumps out too much of one or more adrenal hormones. This can lead to real, noticeable health effects depending on which hormone is overproduced. Even functioning adenomas are benign growths, but the hormone excess they cause often does need to be addressed.
Symptoms of Functioning Adenomas
The symptoms you’d experience depend entirely on which hormone the adenoma is overproducing. The two most common scenarios are cortisol excess and aldosterone excess.
Cortisol Excess (Cushing’s Syndrome)
When an adenoma secretes too much cortisol, you can develop Cushing’s syndrome. This tends to cause a distinctive pattern: weight gain concentrated in the face and midsection, thinning skin that bruises easily, muscle weakness, high blood sugar, and sometimes purple stretch marks on the abdomen. Because these changes develop gradually, many people attribute them to aging or stress before the underlying cause is identified.
Aldosterone Excess (Conn’s Syndrome)
An aldosterone-producing adenoma causes a condition called primary aldosteronism. Aldosterone controls sodium and potassium balance, so when levels run too high, the main result is persistent high blood pressure that doesn’t respond well to standard medications. Some people also develop low potassium, which can cause muscle cramps, weakness, and fatigue. Not everyone with aldosterone excess has low potassium, though, so blood pressure that stubbornly resists treatment is often the strongest clue. Screening is recommended for anyone with blood pressure consistently above 150/100, blood pressure that requires four or more medications to control, or high blood pressure combined with an adrenal mass found on imaging.
In rare cases, an adrenal adenoma can also secrete excess sex hormones, but this is far less common than cortisol or aldosterone overproduction.
How Adrenal Adenomas Are Diagnosed
Because most adenomas are discovered accidentally on imaging, the diagnostic process usually works backward: you already know a mass is there, and the next step is figuring out whether it’s benign and whether it’s producing hormones.
On a CT scan without contrast, the density of the mass gives doctors a strong initial clue. Adrenal adenomas tend to be rich in fat, and fat appears low-density on CT. A reading of 10 Hounsfield units (a measure of tissue density) or below is considered highly reliable for identifying a benign adenoma. Between 10 and 40% of adenomas, however, are “lipid-poor,” meaning they contain less fat and measure above that threshold. For those masses, a follow-up scan with contrast dye can help. Doctors look at how quickly the mass releases the contrast dye afterward. Benign adenomas tend to wash out the dye rapidly, while malignant masses hold onto it longer.
Current guidelines simplify the imaging follow-up. If a mass is small (4 cm or under), measures 20 Hounsfield units or less, and appears uniform on a noncontrast CT, it’s considered benign and no further imaging is needed. Masses that measure above 20 Hounsfield units but are still under 4 cm typically get a repeat scan in 6 to 12 months just to confirm they aren’t growing. Masses over 4 cm with higher density readings warrant closer attention and often a referral to a specialist team.
Regardless of what the imaging shows, a hormonal evaluation is recommended for all adrenal masses. Blood and urine tests check for overproduction of cortisol, aldosterone, and adrenaline-related hormones to rule out both functioning adenomas and a rarer adrenal tumor called a pheochromocytoma.
Risk of an Adenoma Becoming Cancerous
This is one of the most common concerns people have after learning about an adrenal mass, and the numbers are reassuring. The chance of a benign adrenal adenoma transforming into adrenal cancer is less than 1%. A meta-analysis of long-term follow-up studies found that only about 0.2% of incidentally discovered adrenal masses turned out to be or become cancerous over time.
Size is the most important factor. Tumors under 4 cm carry very low risk. Between 4 and 6 cm, the malignancy rate rises to about 2%. Above 6 cm, it jumps to roughly 25%. This is why the 4 cm mark serves as a key threshold in clinical decision-making: masses that exceed it get more scrutiny, and often a recommendation for surgical removal even if they appear benign on imaging.
When Surgery Is Recommended
Most adrenal adenomas never need to be removed. Surgery is typically recommended in two situations: the adenoma is producing excess hormones that are causing health problems, or the mass is large enough to raise concern about malignancy (generally above 4 cm).
The procedure is usually done laparoscopically, meaning through a few small incisions rather than a large one. The surgeon removes the entire affected adrenal gland. Recovery from laparoscopic surgery is relatively quick, with most people returning to normal activity within a few weeks. Since you have two adrenal glands, the remaining one takes over full hormone production without difficulty.
For functioning adenomas causing Cushing’s syndrome, it’s worth knowing that the remaining adrenal gland may be temporarily sluggish after surgery. When one gland has been overproducing cortisol, the other often dials down its own output in response. It can take weeks to months for the remaining gland to ramp back up, and you may need temporary hormone replacement during that period.
What Follow-Up Looks Like
If your adenoma is small, nonfunctioning, and looks clearly benign on imaging, follow-up may be minimal. Many of these need no repeat imaging at all under current guidelines. For masses that fall into a gray zone on initial scans, a repeat CT in 6 to 12 months confirms the adenoma isn’t growing, which is usually the end of the monitoring process. Hormonal testing may also be repeated if your initial results were borderline or if new symptoms develop.
The risk of a small, stable, nonfunctioning adenoma becoming either hormonally active or malignant during follow-up is under 1% for each scenario. For most people, an adrenal adenoma is a finding that requires some initial testing, a bit of watchful waiting, and then fades into the background of their medical history.