Thickening of the left adrenal gland, usually spotted on a CT scan done for an unrelated reason, is one of the most common incidental findings in abdominal imaging. The vast majority of these findings turn out to be benign and non-functional, meaning they produce no excess hormones and pose no immediate health threat. An umbrella review covering over a thousand adrenal incidentalomas found the rate of malignancy to be well under one percent, while roughly 12 percent of cases involved subtle hormonal overproduction.1BMJ. Prevalence and outcomes of incidental imaging findings: umbrella review Still, the finding warrants a structured workup because a small but real fraction of thickened adrenal glands do signal a hormonal disorder, a genetic condition, or, rarely, something more serious.
What Counts as “Thickened”
Your adrenal glands sit on top of each kidney and are shaped differently on each side. The left gland is typically larger and more elongated, often described as crescent- or semilunar-shaped, hugging the upper-inner border of the left kidney. A normal adrenal body measures under about 10 to 12 mm, and the limbs (the thinner arms extending from the body) normally measure under 5 to 6 mm. Many radiologists have long used a 10 mm cut-off for limb thickness, beyond which the gland is flagged as abnormal.2PubMed Central. Normal adrenal gland thickness on computerized tomography in an Asian Indian adult population
In practice, those cut-offs are rough guides. A study of Nepalese adults found average left adrenal limb thickness was around 4 mm and the body around 6 mm, with radiologists also comparing limb thickness to the nearby diaphragmatic crus as a reference point. In that study, over 89 percent of people had a limb-to-crus ratio under one on the left side, confirming that a limb thicker than the diaphragmatic crus beside it raises suspicion.3Medical Journal of Shree Birendra Hospital. Normal Adrenal Gland Thickness on Computed Tomography in Nepalese Adults Presenting to Tertiary Referral Hospital The point is that “thickening” on your radiology report means the gland exceeded an expected size range, prompting your doctor to investigate further.
Why the Left Gland Gets Flagged More Often
You might wonder whether left-sided thickening is more worrying than right-sided thickening. The left adrenal gland is inherently larger and more elongated than the right, which makes subtle changes in its size easier to spot on imaging. The right gland is smaller and tucked behind the liver, where partial-volume effects from surrounding tissue can obscure its edges. As a result, radiologists detect left-sided abnormalities with somewhat more confidence, and incidental reports of left adrenal thickening come up frequently. Whether the thickening is on the left or the right does not, by itself, predict whether it is something harmful. One retrospective study of incidental adrenal enlargement found that lesion location was not a significant predictor of whether a mass was functionally active.4PubMed Central. Incidental Adrenal Enlargement: An Overview from a Retrospective Study in a Chinese Population
The Most Common Explanation Is a Benign, Quiet Nodule
The single most likely outcome when a thickened adrenal gland is investigated is that it turns out to be a non-functional adrenal adenoma or simple hyperplasia, meaning the tissue has grown somewhat but is not overproducing any hormone. In a Chinese retrospective study of incidentally enlarged adrenal glands, about 69 percent of cases were non-functional after full biochemical workup.4PubMed Central. Incidental Adrenal Enlargement: An Overview from a Retrospective Study in a Chinese Population A separate study at a Brooklyn hospital found that among patients who completed hormonal testing, about 16 percent had abnormal results, but none ultimately needed treatment.5Journal of the Endocrine Society. 12572 Incidental Adrenal Enlargement On Ct Scan In South Brooklyn Health, How Often Is It Functional?
These numbers are reassuring, but they also reveal why doctors do not simply ignore the finding. Roughly one in five to one in three cases does show some hormonal abnormality, and some of those conditions benefit from treatment. The workup is straightforward and largely blood-and-urine based, so the cost of checking is low compared with the risk of missing a treatable condition.
Hormonal Conditions That Can Cause Thickening
When adrenal thickening is not just an innocent bystander, it is often tied to excess production of cortisol or aldosterone. These are the two most clinically relevant hormonal causes.
Subclinical Cortisol Excess
The most common functional finding in incidentally discovered adrenal thickening is mild autonomous cortisol secretion, sometimes called subclinical Cushing’s syndrome. In the umbrella review mentioned earlier, about 12 percent of adrenal incidentalomas fell into this category, though only a tiny fraction progressed to full-blown Cushing’s syndrome with its classic signs of weight gain, easy bruising, and muscle weakness.1BMJ. Prevalence and outcomes of incidental imaging findings: umbrella review In full Cushing’s disease, the problem usually starts with a small tumor in the pituitary gland that overdrives the adrenal glands with too much stimulating hormone, causing both glands to enlarge.6PubMed. Cushing Syndrome: Diagnostic Workup and Imaging Features, With Clinical and Pathologic Correlation Whether surgery is needed for the milder, subclinical version remains debated. Current European guidelines recommend a multidisciplinary team approach, weighing the patient’s age, preferences, and whether they have conditions like diabetes or high blood pressure that could be worsened by even mild cortisol excess.7Endocrinology and Metabolism. Recent Updates on the Management of Adrenal Incidentalomas
Primary Aldosteronism
Aldosterone is the hormone that regulates sodium and potassium balance, and overproduction drives up blood pressure. Primary aldosteronism has been found in a meaningful fraction of people with hard-to-control hypertension. The main causes are a small aldosterone-producing adenoma or bilateral hyperplasia, but there is a rarer form involving unilateral adrenal hyperplasia where one gland thickens on its own and overproduces aldosterone.8PubMed Central. Primary aldosteronism caused by unilateral adrenal hyperplasia If you have high blood pressure and a thickened left adrenal gland, your doctor will likely test your aldosterone-to-renin ratio as part of the initial screening.
Congenital Adrenal Hyperplasia
Not all adrenal thickening develops in adulthood. Congenital adrenal hyperplasia is a group of inherited conditions in which the adrenal glands lack an enzyme needed to produce cortisol efficiently. The most common form involves a deficiency of an enzyme called 21-hydroxylase, which accounts for about 95 percent of cases.9PubMed Central. Nonclassic Congenital Adrenal Hyperplasia: What Do Endocrinologists Need to Know? When cortisol production is impaired, the pituitary gland keeps sending signals to the adrenal glands to work harder. That chronic stimulation causes the glands to enlarge over time and to shunt steroid precursors into alternative pathways, leading to excess androgen production.10Biology and management. Congenital adrenal hyperplasia: 21-hydroxylase deficiency and 11-hydroxylase deficiency
The milder, “nonclassic” form of 21-hydroxylase deficiency can go undiagnosed until adulthood and may first come to attention when imaging reveals unexpectedly large adrenal glands. In women, symptoms often include irregular periods, acne, or excess body hair. In men, the condition can be nearly silent aside from the imaging finding. It is inherited in an autosomal recessive pattern, meaning both parents must carry a copy of the gene variant.
Chronic Stress and Adrenal Size
Chronic psychological or physiological stress can also change adrenal gland size over time, though this is more of a research observation than something radiologists typically diagnose on a scan. The stress-response system linking the brain to the adrenal glands can take on several forms under prolonged activation, including sustained overproduction of cortisol and, eventually, measurable growth of the glands themselves.11PubMed Central. Regulation of the Hypothalamic-Pituitary-Adrenocortical Stress Response Animal research has shown that chronic variable stress leads to both an increase in the number of adrenal cells (hyperplasia) and an increase in cell size (hypertrophy) in specific zones of the gland.12PubMed. Chronic stress induces adrenal hyperplasia and hypertrophy in a subregion-specific manner In humans, this mechanism is thought to contribute to adrenal enlargement in conditions like major depression and post-traumatic stress disorder, though it would rarely be the sole explanation for a radiologist flagging adrenal thickening on a scan.
Less Common but Important Causes
Adrenal Hemorrhage and Vascular Congestion
In acute settings, adrenal thickening can reflect bleeding into the gland. This happens most often after major trauma, surgery, or in people on blood-thinning medications. A case series documented that adrenal congestion, visible as gland thickening and surrounding fat inflammation on CT, can precede outright hemorrhage. The proposed mechanism involves a mismatch between the rich arterial blood supply to the adrenal gland and the limited number of draining veins, creating vulnerability to vascular congestion and eventual bleeding.13PubMed. Adrenal congestion preceding adrenal hemorrhage on CT imaging: a case series Adrenal hemorrhage is usually managed conservatively unless it causes adrenal insufficiency or is life-threatening in volume.
Infections
Certain infections can settle in the adrenal glands and cause them to swell. Histoplasmosis, a fungal infection caused by inhaling spores from contaminated soil, is one well-known example. In immunosuppressed individuals, disseminated histoplasmosis can reach the adrenal glands and cause unilateral or bilateral enlargement, sometimes accompanied by fever, weight loss, and eventually adrenal insufficiency.14Journal of the ASEAN Federation of Endocrine Societies. ADRENAL HISTOPLASMOSIS AND BILATERAL ADRENAL ENLARGEMENT Tuberculosis is another classic cause of adrenal enlargement, particularly in parts of the world where TB remains prevalent. These infections are far less common causes of a thickened adrenal gland than benign adenomas, but they are worth knowing about if you have a weakened immune system or live in an area where these infections are endemic.
Pheochromocytoma and Medullary Hyperplasia
The inner part of the adrenal gland, called the medulla, can develop its own growths. Pheochromocytomas are tumors that produce adrenaline and related hormones, causing episodes of high blood pressure, racing heart, sweating, and headaches. In people with a genetic syndrome called multiple endocrine neoplasia type 2 (MEN2), the medulla can first undergo a growth phase called adrenal medullary hyperplasia before progressing to a pheochromocytoma. Research on MEN2 patients found that medullary hyperplasia and pheochromocytomas share the same molecular abnormalities, leading some experts to argue that medullary hyperplasia in these patients should be treated as an early-stage tumor rather than a benign overgrowth.15PubMed Central. Adrenal medullary hyperplasia is a precursor lesion for pheochromocytoma in MEN2 syndrome
Metastatic Cancer
The adrenal glands are a relatively common destination for cancer that has spread from elsewhere in the body, particularly from lung, breast, and kidney cancers. In rare instances, the adrenal metastasis is discovered before the primary cancer is even known to exist. One case report described a unilateral adrenal mass initially thought to be a primary adrenal cancer but found on pathology after surgery to be a metastasis from an unknown primary tumor.16Journal of the Endocrine Society. 6485 Unilateral Adrenal Metastasis From Unknown Primary Carcinoma Mimicking Primary Adrenocortical Carcinoma Despite the anxiety this possibility causes, the overall risk of malignancy in incidentally found adrenal masses is extremely low in people without a known cancer history.
How Doctors Figure Out What Is Going On
The standard approach to a thickened adrenal gland has two tracks running in parallel: imaging characterization and hormonal testing.
On the imaging side, the first question is whether the tissue looks like a typical benign adenoma. Many adrenal adenomas are rich in intracellular fat, which gives them a characteristically low density on a non-contrast CT scan, measured in Hounsfield units. A large study with surgical pathology as the reference standard found that an unenhanced CT density at or below 10 Hounsfield units reliably distinguished adenomas and hyperplasias from non-adenomas, with perfect specificity.17PubMed. Clinical utility of noncontrast computed tomography attenuation value (hounsfield units) to differentiate adrenal adenomas/hyperplasias from nonadenomas: Cleveland Clinic experience The problem is that about a third of lipid-rich adenomas measure above that 10-unit threshold, which is where MRI with chemical shift imaging becomes useful. Chemical shift MRI detects intracellular fat by comparing two types of signal, and studies have shown it can identify adenomas that CT alone would miss.18PubMed. Comparison of unenhanced CT and chemical shift MRI in evaluating lipid-rich adrenal adenomas19PubMed Central. Magnetic resonance imaging of adrenal gland: state of the art
The harder imaging challenge is distinguishing thickening from hyperplasia versus a small adenoma. Research has shown significant overlap in CT density and contrast washout patterns between the two, meaning imaging alone often cannot make that call with certainty.20PubMed. Differentiation of Adrenal Hyperplasia From Adenoma by Use of CT Densitometry and Percentage Washout Fortunately, the distinction matters less than you might think. What matters clinically is whether the gland is producing excess hormone and whether the imaging features suggest malignancy, not whether the tissue pattern is technically an adenoma or hyperplasia.
On the hormonal side, all incidentally discovered adrenal masses should undergo screening blood and urine tests to rule out excess cortisol, excess catecholamines (the adrenaline-family hormones that indicate pheochromocytoma), and, in people with high blood pressure, excess aldosterone. These tests are simple, widely available, and can be completed with a combination of blood draws and a 24-hour urine collection. Only if the results are abnormal does the workup escalate to more specialized testing or a surgical consultation.
When Nodular Shape Matters More Than Size Alone
One detail worth knowing is that the shape and texture of adrenal thickening can carry more clinical weight than the size measurement by itself. Diffuse, smooth thickening of the gland often reflects hyperplasia from an external stimulus, like prolonged cortisol drive from the pituitary or chronic stress. A discrete nodule sitting within or on the gland is a different finding. In the Chinese retrospective study, nodular adrenal enlargement was a significant risk factor for the lesion being hormonally active, with roughly seven times the odds of functional status compared to non-nodular thickening.4PubMed Central. Incidental Adrenal Enlargement: An Overview from a Retrospective Study in a Chinese Population If your radiology report describes a nodular component within the thickened gland, your doctor may pursue the hormonal workup more urgently.
Bilateral Versus Unilateral Thickening
A thickened left adrenal gland in isolation carries a different set of possibilities than thickening of both glands. Bilateral adrenal enlargement tends to point toward systemic causes: pituitary-driven Cushing’s disease, congenital adrenal hyperplasia, or disseminated infections. Unilateral thickening, on the other hand, is more likely to be a localized adenoma, a focal area of hyperplasia, or, in rare cases, a metastatic deposit. Primary aldosteronism from unilateral adrenal hyperplasia is one scenario where a single thickened gland can explain high blood pressure that responds poorly to standard medications.8PubMed Central. Primary aldosteronism caused by unilateral adrenal hyperplasia The laterality of the finding helps your endocrinologist narrow the list of suspects, but it does not change the basic approach: imaging plus hormonal testing.
Genetic Syndromes Worth Screening For
Most adrenal thickening is sporadic, meaning it has no hereditary component. But a handful of genetic syndromes can cause adrenal enlargement that first appears on routine imaging. Primary bilateral macronodular adrenal hyperplasia is a condition where both adrenal glands develop large nodules and often overproduce cortisol. Research has linked this condition to abnormal activation of a signaling pathway inside adrenal cells that drives both cortisol secretion and tissue growth, sometimes through receptors that should not be present in the adrenal gland at all.21PubMed. Diagnosis and management of primary bilateral macronodular adrenal hyperplasia MEN2, discussed earlier, is another inherited syndrome where adrenal medullary growth can be the first sign. If you have a family history of adrenal tumors, thyroid cancer, or endocrine disorders, it is worth mentioning that to your doctor when discussing an incidental adrenal finding.
What Happens After the Initial Workup
If the imaging looks benign and the hormone tests come back normal, most guidelines recommend a follow-up CT scan in 6 to 12 months to make sure the gland has not changed significantly in size. If it remains stable and the biochemistry stays normal, further imaging is generally not needed. For masses that measure over 4 cm, grow significantly on follow-up, or show imaging features suspicious for malignancy, surgical removal is typically recommended regardless of hormonal function. For mild autonomous cortisol secretion, the decision is more nuanced and depends on whether you have related health problems that might improve with surgery.7Endocrinology and Metabolism. Recent Updates on the Management of Adrenal Incidentalomas
One common source of anxiety is the gap between the scan and the test results. Seeing “adrenal thickening” or “adrenal enlargement” on a radiology report can feel alarming, but the vast majority of these findings end up requiring nothing more than a blood test and a follow-up scan. The evidence consistently shows that incidental adrenal findings carry a very low rate of malignancy, and even the hormonally active ones are usually manageable with medication or, when needed, minimally invasive surgery.
Why Some Adrenal Adenomas Fool the Scanner
One frustrating wrinkle in adrenal imaging is that not all benign adenomas behave the same way on a scan. Most adenomas contain enough intracellular fat to appear obviously benign, but a subset called lipid-poor adenomas lack that fat signature and can mimic more concerning masses on CT. Recent MRI research has found that refined chemical-shift techniques can improve the detection of these lipid-poor adenomas, though sensitivity is still imperfect when the adenoma contains very little fat.22PubMed Central. The role of magnetic resonance imaging (MRI) in the detection of intracellular lipid content in adrenal adenomas In these ambiguous cases, a PET scan or a period of watchful waiting with repeat imaging may be needed to reach a confident diagnosis. The key takeaway is that an adrenal mass that does not look classically benign on CT is not necessarily malignant; it may simply be a benign adenoma that happens to be low in fat.