Thickening of the left adrenal gland usually means the gland’s tissue has grown wider than normal but hasn’t formed a distinct lump or tumor. On a CT scan, normal adrenal limbs measure about 5 mm or less in width. When a radiologist describes “thickening,” they’re noting that one or both limbs of the gland exceed that size while still keeping their general shape. In most cases, this finding is benign, but it does require a workup to rule out hormonal problems or, rarely, something more serious.
What Thickening Looks Like on Imaging
Your adrenal glands sit on top of each kidney and have a roughly Y-shaped or inverted V-shaped appearance on cross-sectional imaging. Each arm of that shape is called a limb. Radiologists measure limb width to decide whether a gland looks normal or enlarged. A limb wider than 5 mm is considered thickened, though some studies use a 3 mm cutoff for higher sensitivity.
Thickening differs from a nodule or mass. A nodule is a distinct round growth within the gland, while thickening describes a more diffuse, spread-out enlargement where the gland gets bulkier but retains its normal contour. The medical term for this pattern is adrenal hyperplasia, which simply means the gland tissue has expanded. It can appear smooth and uniform or slightly bumpy with tiny nodules scattered through the tissue.
Why It Happens on the Left Side
Many of the conditions that cause adrenal thickening affect both glands equally. When thickening appears on the left side alone, there are a few possible explanations. The left adrenal gland is a slightly more common site for metastatic disease (cancer that has spread from elsewhere in the body), though isolated thickening without a known primary cancer is overwhelmingly likely to be benign. The risk of an incidentally found adrenal abnormality being malignant in someone with no cancer history is roughly one in a thousand.
Unilateral thickening can also reflect a normal anatomical variant, early hyperplasia that happens to be more prominent on one side, or a small adenoma (a benign growth) that hasn’t yet formed a clearly defined nodule. In practice, the left-versus-right distinction matters less than the gland’s size, density on imaging, and whether it’s producing excess hormones.
Common Causes of Adrenal Thickening
The most frequent cause is adrenal cortical hyperplasia, a non-cancerous overgrowth that can be triggered by several underlying conditions. These include:
- Primary aldosteronism (Conn’s syndrome): The adrenal glands overproduce aldosterone, a hormone that controls sodium and potassium balance. This is one of the most common causes of difficult-to-treat high blood pressure. In many cases, bilateral adrenal hyperplasia is the underlying anatomy rather than a single tumor.
- Cushing’s syndrome: Excess cortisol production, often driven by signals from the pituitary gland, causes both adrenal glands to enlarge over time. The thickening is most noticeable in the limbs of the gland where cortisol-producing tissue is concentrated.
- Congenital adrenal hyperplasia: A group of inherited enzyme deficiencies that cause the adrenal glands to work harder and grow larger, typically present from birth but sometimes diagnosed in adulthood.
- Physiologic stress or chronic illness: Prolonged physical stress, critical illness, or long-term stimulation of the adrenal glands can cause mild, reversible thickening.
Benign adenomas are another possibility. These small, noncancerous tumors are extremely common and are found incidentally in 1 to 5 percent of all abdominal CT scans, with prevalence increasing with age. Certain genetic conditions like multiple endocrine neoplasia type 1 and familial adenomatous polyposis raise the likelihood. Obesity and tobacco use are also associated with a higher chance of developing an adenoma.
Symptoms That May Point to a Cause
Adrenal thickening itself doesn’t cause symptoms. What matters is whether the enlarged tissue is producing excess hormones. Many cases are “nonfunctioning,” meaning the gland is bigger but hormonally quiet, and you feel perfectly fine.
If the thickening is hormonally active, the symptoms depend on which hormone is overproduced. Excess aldosterone typically causes high blood pressure that resists standard treatment, along with low potassium levels that can trigger muscle weakness, cramping, or fatigue. The classic triad that raises suspicion for a mineralocorticoid-producing problem is hypertension, unexplained low potassium, and metabolic alkalosis (a shift in blood chemistry).
Excess cortisol can cause weight gain concentrated in the face and midsection, thinning skin that bruises easily, mood changes, high blood sugar, and muscle weakness. A rare but important possibility is pheochromocytoma, a tumor that produces adrenaline-like hormones and causes episodes of severe high blood pressure, rapid heartbeat, sweating, and headaches. Although pheochromocytomas usually form distinct masses rather than diffuse thickening, they must be ruled out because of their cardiovascular risks.
What Testing Looks Like
European and North American guidelines agree that every incidentally discovered adrenal abnormality needs two things evaluated: whether it’s hormonally active and whether it could be malignant. Your doctor will likely start with a physical exam looking for signs of hormone excess, then order blood and urine tests.
The standard hormonal workup typically covers three areas. First, cortisol overproduction is screened with an overnight dexamethasone suppression test, where you take a small steroid pill at bedtime and have your cortisol measured the next morning. If cortisol drops below a specific threshold, overproduction is effectively ruled out. This test catches autonomous cortisol secretion with sensitivity between 73 and 100 percent. Second, pheochromocytoma is checked through plasma or urine metanephrines, breakdown products of adrenaline-like hormones, with about 95 percent sensitivity and specificity. Third, if you have high blood pressure or unexplained low potassium, your doctor will measure the ratio of aldosterone to renin in your blood to screen for primary aldosteronism.
On the imaging side, the density of adrenal tissue on an unenhanced CT scan provides a strong clue about whether a lesion is benign. Tissue that measures 10 Hounsfield units or less (a measure of density on CT) is almost certainly a lipid-rich adenoma, and no further imaging is needed. Tissue at 0 Hounsfield units or below is virtually guaranteed to be benign. If the density is higher, additional imaging with contrast washout analysis or MRI may be used to further characterize the tissue.
Follow-Up and What to Expect
If your hormonal tests come back normal and the imaging characteristics look benign, the finding is typically managed with periodic monitoring. The purpose of follow-up imaging, usually a repeat CT at 6 to 12 months, is to confirm the thickening is stable and not slowly growing. Stability over time is strong reassurance that the finding is benign.
If hormonal testing reveals excess aldosterone, cortisol, or catecholamines, the next steps depend on the specific diagnosis. A single hormone-producing adenoma on one side may be a candidate for surgical removal, while bilateral hyperplasia causing excess aldosterone is usually managed with medication that blocks aldosterone’s effects. The key distinction, and the reason the workup exists, is to separate the small number of cases that need intervention from the large majority that simply need observation.
For people with no history of cancer and an adrenal finding that measures under 4 cm with benign imaging features, the overall prognosis is excellent. Most of these findings never cause problems and are simply one of the many incidental discoveries that modern high-resolution imaging picks up.