An adrenal lesion is any abnormal growth or mass found in one or both of your adrenal glands, the small hormone-producing organs that sit on top of each kidney. Most adrenal lesions are discovered by accident during a CT scan or MRI ordered for something else entirely, which is why doctors call them “adrenal incidentalomas.” The vast majority turn out to be harmless, non-cancerous adenomas, but evaluation still matters because some lesions produce excess hormones that quietly damage your cardiovascular system, and a small fraction are malignant. The workup involves a combination of imaging characteristics and blood or urine tests, and the process can feel confusing if nobody walks you through what each step is actually looking for.
How Common Are Adrenal Lesions
Adrenal lesions are far more common than most people realize. In a review of over 65,000 abdominal CT scans in patients with no known cancer, about 5% had an adrenal mass.
1PubMed. The incidental adrenal mass on CT: prevalence of adrenal disease in 1,049 consecutive adrenal masses in patients with no known malignancyA Brazilian hospital study found a somewhat lower rate of roughly 2.5%, with older age and male sex both linked to higher odds of discovery.
2Arq Bras Endocrinol Metab. Prevalence of adrenal incidentaloma at computed tomography (chest and abdominal) in a general hospital in BrazilAmong cancer patients, the numbers climb steeply: a large cancer-center analysis of over 58,000 patients reported adrenal abnormalities in about 13% of abdominal CT reports, though that figure includes metastases alongside benign findings.
3PubMed Central. The prevalence and spectrum of reported incidental adrenal abnormalities in abdominal computed tomography of cancer patients: The experience of a comprehensive cancer centerThe practical takeaway is that if you have been told you have an adrenal lesion, you are in very common company. Most of these findings are incidental and benign, but every one of them warrants at least a basic workup to rule out hormone overproduction and cancer.
What Types of Lesions Can Appear
Adrenal lesions fall along two independent axes: whether they are benign or malignant, and whether they are hormonally active (“functioning”) or silent (“non-functioning”). Most are both benign and non-functioning, which is the best-case scenario. In one detailed series of 139 patients evaluated for adrenal incidentalomas, about 44% had non-functional benign adenomas. Roughly 37% had functioning lesions, meaning the mass was quietly overproducing a hormone. About 11% were malignant.
4Archives of Internal Medicine. Evaluation of Functional and Malignant Adrenal IncidentalomasAmong the functioning lesions in that series, cortisol excess was the most frequent culprit, followed by aldosterone overproduction and catecholamine-secreting tumors (pheochromocytomas). That matters because each of those hormone patterns carries different health risks and calls for a different set of lab tests. Certain lesion types also have characteristic appearances on imaging. Lipid-rich adenomas and myelolipomas, for instance, have features on CT that make them easy to identify without any further testing.
5PubMed Central. Pitfalls and differential diagnosis on adrenal lesions: current concepts in CT/MR imaging: a narrative reviewCT Imaging and the Hounsfield Unit Threshold
The first and most informative tool for evaluating an adrenal lesion is usually the CT scan that found it. Radiologists measure the density of the mass in Hounsfield units (HU), a scale where water is 0 and denser tissue scores higher. Benign adrenal adenomas tend to be rich in intracellular fat, which makes them appear less dense. For decades, the standard threshold has been 10 HU or below on an unenhanced (non-contrast) CT: if the lesion measures at or under 10 HU, it is almost certainly a benign adenoma and generally needs no further imaging workup.
That threshold is highly specific but not very sensitive. One surgical series found that using 10 HU as the cutoff correctly identified adenomas with about 94% specificity but only about 48% sensitivity, meaning it catches the ones it flags very reliably but misses over half of all adenomas because many contain less fat and measure above 10 HU. Raising the threshold to 16 HU improved sensitivity to around 65% without sacrificing specificity.
6PubMed Central. Utility of the 10 Hounsfield Unit Threshold for Identifying Adrenal Adenomas: Can We Improve?What this means in practice is that a low-density lesion on CT is very reassuring, but a lesion measuring above 10 HU is not automatically worrisome. It just needs more investigation.
Contrast Washout and Its Limits
When a lesion measures above 10 HU and its nature is uncertain, the traditional next step has been a washout CT, where the scan is repeated after contrast dye is injected and then again after a delay. Benign adenomas tend to lose contrast quickly, while malignant lesions hold onto it. Early studies found that a relative washout above 50% on delayed scans correctly classified nearly all benign versus malignant lesions in their cohorts.
7PubMed. Characterization of indeterminate (lipid-poor) adrenal masses: use of washout characteristics at contrast-enhanced CTMore recent evidence, however, has seriously challenged the reliability of washout CT for incidental adrenal masses. A large multi-institution study of 336 incidentalomas above 10 HU found that the overwhelming majority were benign regardless of washout pattern. Among lesions under 4 cm, malignancy was vanishingly rare at about 0.3%, and washout did not meaningfully distinguish benign from malignant masses in that size range. Even for masses over 4 cm, the difference between those that washed out and those that did not was not statistically significant. The authors concluded that washout CT “with the established thresholds is insufficient to reliably diagnose adrenal masses,” and the test’s added value in true incidentaloma populations appears negligible.
8PubMed Central. Washed up: the end of an era for adrenal incidentaloma CTThis is an area of active debate, and many radiology departments still perform washout protocols. But the trend is moving toward relying less on washout and more on lesion size, stability over time, and hormonal testing.
MRI and PET Scans
MRI offers an alternative way to characterize adrenal lesions, especially those that remain unclear after CT. The most useful MRI technique is called chemical-shift imaging, which detects the presence of intracellular fat. In a lipid-containing adenoma, the signal on one sequence drops noticeably compared with another, giving radiologists a clear marker of benign tissue. One study found that unenhanced CT characterized about 36% of adrenal masses, and chemical-shift MRI then resolved another 60%, leaving only about 4% of patients needing an invasive biopsy.
9Journal of Nuclear Medicine. 18F-FDG PET in Characterizing Adrenal Lesions Detected on CT or MRIThere are exceptions. Rare adrenal cancers and certain metastases from kidney, liver, or fat-derived tumors can also contain enough lipid to mimic adenomas on chemical-shift MRI. This is uncommon, but it means MRI is not foolproof. PET scanning, which uses a radioactive sugar tracer to highlight metabolically active tissue, can help in patients with a known cancer elsewhere, where the main question is whether the adrenal lesion is a metastasis. A lesion that does not light up on PET is unlikely to be a metastasis.
Hormonal Testing
Imaging tells you what the lesion looks like; hormonal testing tells you what it is doing. Even if a lesion appears perfectly benign on a scan, it may be silently pumping out excess hormones. The standard workup screens for three main conditions.
Autonomous Cortisol Secretion
The most common hormonal abnormality in adrenal incidentalomas is mild cortisol overproduction, often called “autonomous cortisol secretion.” It does not cause the dramatic weight gain and muscle wasting of full-blown Cushing syndrome, but it is associated with higher rates of high blood pressure, diabetes, and cardiovascular problems. The standard screening test is the overnight dexamethasone suppression test: you take a small dose of dexamethasone at night, and your blood cortisol is measured the next morning. In a healthy system, cortisol drops; in autonomous secretion, it stays elevated.
The debate is over where exactly to draw the line. Research has explored various thresholds. One large study found that patients with a post-test cortisol above roughly 1.2 micrograms per deciliter had significantly higher rates of hypertension and diabetes compared with those who suppressed below that level, even after adjusting for age, obesity, and other factors.
10PubMed Central. Dexamethasone Suppression Testing in Patients with Adrenal Incidentalomas with/Without Mild Autonomous Cortisol Secretion: Spectrum of Cortisol Cutoffs and Additional Assays (An Updated Analysis)Current European guidelines do not recommend repeating the hormonal workup on follow-up if the initial screening is normal and no new symptoms appear.
11Endocrinology and Metabolism. Recent Updates on the Management of Adrenal IncidentalomasPheochromocytoma Screening
Pheochromocytomas are catecholamine-producing tumors that can cause dangerous blood pressure spikes. Missing one before surgery is a serious safety concern because manipulating the tumor during an operation can trigger a life-threatening hypertensive crisis. Screening involves measuring metanephrines, the breakdown products of catecholamines. Plasma free metanephrines have a sensitivity of about 97 to 99%, making them excellent at ruling out the diagnosis.
12JAMA. Biochemical Diagnosis of Pheochromocytoma: Which Test Is Best?The trade-off is that plasma testing produces more false positives than 24-hour urine collections of metanephrines and catecholamines, which have higher specificity (around 98%). For that reason, some centers prefer urine testing for low-risk patients with incidental adrenal findings, reserving plasma metanephrines for patients with a family history of hereditary endocrine syndromes or clinical symptoms strongly suggestive of pheochromocytoma.
13PubMed. A comparison of biochemical tests for pheochromocytoma: measurement of fractionated plasma metanephrines compared with the combination of 24-hour urinary metanephrines and catecholaminesPrimary Aldosteronism
If you have high blood pressure and an adrenal lesion, your doctor should check for primary aldosteronism, a condition where the adrenal gland overproduces aldosterone, driving up blood pressure and lowering potassium. The screening test is the aldosterone-to-renin ratio. In adrenal incidentaloma populations, the prevalence of confirmed primary aldosteronism has been reported at roughly 3 to 4% of patients, with nearly all affected individuals already having hypertension at the time of diagnosis.
14PubMed Central. Primary aldosteronism in patients with adrenal incidentaloma: Is screening appropriate for everyone?15PubMed. Determination of the aldosterone/renin ratio in 269 patients with adrenal incidentaloma
If aldosteronism is confirmed and surgery is being considered, a specialized procedure called adrenal vein sampling is often needed to determine which gland is the source. This involves threading a catheter into the adrenal veins and measuring hormone levels directly. The procedure can be technically challenging, and bilateral cannulation fails in a meaningful number of cases. Recent research has shown that even unilaterally successful sampling can provide useful diagnostic information.
16PubMed. Unilaterally Selective Adrenal Vein Sampling for Identification of Surgically Curable Primary AldosteronismSize, Growth, and Malignancy Risk
Lesion size is one of the strongest predictors of whether an adrenal mass is malignant. Most guidelines use 4 cm as the threshold above which malignancy risk rises meaningfully, though some disagreement exists about the exact number.
17PubMed Central. Adrenal Incidentaloma Controversial Size RecommendationsBelow 4 cm and with a benign appearance on CT, the risk of cancer is extremely low. In the large multi-institution incidentaloma study discussed earlier, the malignancy rate for lesions under 4 cm with density above 10 HU was just 0.3%.
8PubMed Central. Washed up: the end of an era for adrenal incidentaloma CTGrowth rate is equally telling. A study comparing adenomas with malignant nodules found that adenomas grew at an average of about 1 mm per year, while malignant lesions grew at an average of over 58 mm per year. A growth rate of 3 mm per year cleanly separated benign from malignant in that cohort, with perfect sensitivity and specificity.
18PubMed. Differences in Growth Rate on CT of Adrenal Adenomas and Malignant Adrenal NodulesAnother study proposed a lower absolute growth threshold of 0.8 cm total increase as the best balance between catching cancers and avoiding unnecessary surgery.
19Endocrine Practice. Change in Adrenal Mass Size as a Predictor of a Malignant TumorThis is why follow-up imaging is part of the standard protocol for lesions that cannot be definitively characterized at first: stability over time is strong evidence of benignity.
When Biopsy Is Considered
Adrenal biopsy is rarely needed and is reserved for situations where imaging and lab tests cannot settle the diagnosis. The classic scenario is a patient with a known cancer elsewhere and a new adrenal mass that does not have benign imaging features. In that setting, knowing whether the mass is a metastasis changes treatment planning substantially. Image-guided needle biopsy can provide a definitive tissue diagnosis when other methods fall short.
20PubMed Central. Image-guided adrenal and renal biopsyOne absolute prerequisite before any adrenal biopsy is biochemically ruling out pheochromocytoma. Puncturing a pheochromocytoma with a needle can trigger a massive catecholamine surge and a hypertensive emergency. As long as metanephrines are normal, the procedure is generally safe, though minor complications like bleeding or pain at the puncture site can occur.
When Surgery Is Recommended
Surgery is indicated for all functioning adrenal tumors regardless of size, for lesions with imaging features suspicious for malignancy, and for non-functioning tumors above the size cutoff where malignancy risk becomes appreciable.
21PubMed Central. Surgical Indications and Techniques for AdrenalectomyLaparoscopic (minimally invasive) adrenalectomy is the standard approach for most of these cases and has been for over two decades. The upper size limit considered safe for laparoscopy has expanded over time, from around 6 cm to 10–12 cm depending on the surgeon’s experience. Open surgery is reserved for large tumors with signs of local invasion or confirmed malignancy where a wider surgical margin is needed.
22PubMed Central. Laparoscopic adrenalectomy: An updateBilateral Lesions and Genetic Syndromes
When adrenal masses appear on both sides, the evaluation becomes more nuanced. Bilateral adrenal adenomas are common enough on their own, especially in older adults, and are usually benign. But bilateral masses also raise the possibility of hereditary tumor syndromes. In one series of patients with bilateral pheochromocytomas, about two-thirds of index cases had a syndromic or familial association, most frequently Von Hippel-Lindau disease and multiple endocrine neoplasia type 2.
23PubMed Central. Bilateral adrenal masses: a single-centre experienceBilateral micronodular and macronodular adrenal disease can also cause cortisol overproduction and is frequently linked to germline mutations.
24Ewha Medical Journal. Overview of endocrine tumor syndromes manifesting as adrenal tumorsIf you have bilateral adrenal lesions, particularly pheochromocytomas or Cushing-type cortisol excess, your doctor may recommend genetic testing and screening of close relatives.
Steroid Profiling for Detecting Adrenal Cancer
Adrenocortical carcinoma (ACC) is the nightmare scenario with an adrenal lesion, but it is rare. It also tends to be biochemically noisy, churning out unusual patterns of steroid hormones and their precursors. Researchers have developed urine and blood steroid profiling methods that exploit this messiness. By measuring a panel of steroid metabolites using mass spectrometry, studies have achieved accuracy in the range of 90 to 96% for distinguishing ACC from benign adenomas.
25The Journal of Clinical Endocrinology & Metabolism. Urine Steroid Metabolomics as a Biomarker Tool for Detecting Malignancy in Adrenal Tumors26European Journal of Endocrinology. Plasma steroid metabolome profiling for the diagnosis of adrenocortical carcinoma
These tests are not yet part of routine clinical practice everywhere, but they represent a promising non-invasive tool. Three independent studies with cohorts of at least 100 patients have confirmed significant differences in steroid excretion patterns between benign and malignant adrenal tumors.
27PubMed. Diagnosis of a malignant adrenal mass: the role of urinary steroid metabolite profilingIn the future, steroid profiling may help avoid unnecessary surgery on large but benign lesions, while flagging smaller cancers that might otherwise be monitored too conservatively.
Artificial Intelligence and Radiomics
A newer area of development is using machine-learning algorithms to analyze the texture and mathematical features of adrenal lesions on CT and MRI, an approach called radiomics. A systematic review of these studies found that machine-learning models have been built for several tasks: distinguishing benign from malignant lesions, classifying specific subtypes like lipid-poor adenomas and pheochromocytomas, and even differentiating hormone-secreting from non-secreting incidentalomas. All published models achieved diagnostic accuracy above an area-under-the-curve of 0.80, and several outperformed conventional radiologist assessments.
28PubMed Central. Artificial intelligence and radiomics applications in adrenal lesions: a systematic reviewThe caveat is that these studies are limited by small sample sizes and have not yet been validated in large, prospective, multi-center trials. In one early study, an unsupervised machine-learning approach correctly predicted malignancy in seven of eight adrenocortical carcinomas across all imaging phases.
29BJS Open. Radiomics: a new tool to differentiate adrenocortical adenoma from carcinomaThe technology is not ready to replace current evaluation methods, but it may eventually help standardize interpretation and reduce the number of indeterminate lesions that currently require follow-up imaging or surgery just because a human reader could not tell what they were looking at.