What Scans are Best for Adrenal Tumors?
There are five main imaging tests to examine the adrenal glands (and the rest of the abdomen) for the presence of a tumor: CT, MRI, nuclear medicine scans, PET scans and ultrasound. (The word "tumor" simply means "mass"; these can be benign or malignant.) Some of these tests are better than others and are therefore used routinely, while one or two are used infrequently yet can yield important information when positive.
Dr. Carling meticulously studies a CT scan prior to a Mini Back Scope Adrenalectomy (MBSA) operation. Dr. Carling has reviewed thousands of adrenal tumor scans.
When we look at the imaging of the adrenal gland, whether it is an ultrasound, CT, MRI, nuclear medicine (MIBG, PET, etc.) scan or other imaging study, we need to have a whole-person approach and evaluate all aspects of the tumor and the patient. We carefully analyze the "imaging phenotype" of the tumor. The "imaging phenotype" describes all aspects of what the tumor looks like on your scan and helps us arrive at the correct diagnosis, including the likelihood of cancer. It should be noted, this is far from a perfect science. In many cases we can never know for sure whether the tumor is cancerous short of removing it via adrenalectomy. Since the interpretation of adrenal imaging is not black and white, you need a team and a surgeon who is experienced and has great judgment.
What do expert adrenal doctors look for on adrenal scans? What we look for on an imaging study (scan) is a combination of more than a dozen criteria giving us a total impression, called the "imaging phenotype". For instance, we carefully examine the size and the shape of the tumor. That means we will look at whether the borders are smooth or irregular, whether the margins are clear or unclear, and so forth.
The key and most important points of adrenal imaging and adrenal scanning are:
Adrenal protocol, contrast-enhanced CT scan demonstrating a right adrenal adenoma (4.4 cm, arrow), causing adrenal hypercortisolism (adrenal Cushing syndrome). Benign adrenal adenomas are typically smooth, round or oval, homogeneous and lipid-rich.
- A benign cortical adenoma is the most common adrenal tumor and it is almost always round. A cortical adenoma is an adrenal tumor that grows from the adrenal cortex -- the outermost layer of the adrenal gland. (See adrenal anatomy for more information.)
- The gold standard of adrenal imaging is a CT scan. A non-contrast CT is the first step: it measures the density of the tumor in Hounsfield units (HU). A uniform tumor measuring 10 HU or less is a benign, lipid-rich adenoma, and for most patients this is the only scan needed to characterize the tumor.
- When the tumor measures more than 10 HU or looks irregular, it is indeterminate and needs more: an “adrenal-protocol” CT with contrast and washout measurements, an MRI or a PET scan. A contrast-enhanced CT is also valuable for planning surgery. Contrast is avoided if you have an allergy to contrast dye or reduced kidney function.
- MRI is rarely needed and, in most adults, should not be the first scan. MRI is preferred in pregnancy and in children, to avoid radiation.
- Nuclear medicine scans are rarely necessary. They are helpful in some very specific settings that few doctors will ever see.
- Ultrasound is not accurate enough for the adrenal glands in adults.
- The scan shows what a tumor looks like, not what it does. Every adrenal tumor also needs hormone testing, however benign it looks.
Adrenal CT Scans and Hounsfield Units
The CT scan (also called CAT scan) is very accurate at examining the adrenal glands and other abdominal structures and can be used on any type of adrenal tumor. Like the other tests in this group, the CT scan is painless. It takes only a few minutes to complete. The pictures are very good at demonstrating tumors throughout the body, and very accurate measurements can be taken, which helps the planning of subsequent therapies. CT is the first-level imaging modality for the evaluation of adrenal lesions since it is fast and gives great resolution.The non-contrast CT scan is the first step in characterizing an adrenal tumor. On an unenhanced CT (no IV contrast is given to the patient), adrenal adenomas are usually well-demarcated round or oval lesions, with homogeneous and relatively low attenuation values (10 Hounsfield units [HU] or less), due to their high fat content. A homogeneous tumor of 10 HU or less is benign on imaging, and if it also makes no excess hormone it generally needs no repeated imaging. Unfortunately, unenhanced (non-contrast) CT alone is not always diagnostic, since 15–30% of adenomas are lipid-poor, thereby showing higher attenuation values. In these cases, additional imaging after intravenous contrast administration (the “adrenal protocol”, contrast-enhanced CT scan) can help to differentiate adenomas from non-adenomas. This requires a further late phase after the venous phase, commonly 15 minutes after the contrast is given. A contrast-enhanced scan is also our preferred study for planning surgery.
A right 6 cm pheochromocytoma seen on a CT scan (arrow) and after removal. Pheochromocytomas are vascular and may appear variable with solid, cystic, calcified, and necrotic components.
A note about the technical detail: this is by far the most technical page of this website. We include it because many doctors who see a patient with an adrenal tumor read this page, and the detail helps them take better care of you. Don't worry about the technical parts if you are not a doctor; keep reading, because most of this website is written for patients as well as doctors.
The absolute percentage washout (APW) of contrast from the adrenal tumor can then be calculated using a formula. The relative percentage washout (RPW) is used when an unenhanced CT value is not available. An APW above 60% or an RPW above 40% at 15 minutes after contrast administration suggests a benign adenoma.
This method can, to some degree of certainty, differentiate benign adenomas, which enhance quickly and show rapid washout, from non-adenomas such as adrenocortical cancer and metastases, which instead demonstrate strong enhancement but prolonged washout. Washout can help, but it cannot be relied on alone to exclude cancer or a pheochromocytoma. A tumor that remains indeterminate needs further evaluation (for example MRI or FDG-PET, or a repeat scan after 6 to 12 months) or removal. Read more about the risk of cancer in an adrenal tumor.
Pheochromocytomas on Contrast-Enhanced CT Scans. Pheochromocytomas can present with solid, cystic, calcific, and/or necrotic components--quite variable. Smaller pheos tend to display a more uniform attenuation, with a density of 40–50 HU. After contrast administration, pheochromocytomas enhance avidly (meaning turn very bright) with some of them showing higher enhancement on the portal venous phase and others on the arterial phase; nevertheless, their APW and RPW are similar to those of adenomas. Therefore, pheochromocytomas often cannot be reliably differentiated from adenomas using CT washout protocols. When lesions are quite large (>6 cm), intralesional hemorrhage, necrosis, or calcifications can be observed.
A left adrenocortical cancer (arrow) depicted on an adrenal protocol (arterial phase) contrast-enhanced CT, and following removal. Adrenal cancers often display a heterogeneous (variable) appearance due to necrosis, calcifications, and bleeding into the tumor.
Metastases to the adrenal gland (most commonly from carcinomas of the lung, breast and kidney, and from melanoma) appear as focal masses with strong and prolonged enhancement on the portal venous phase and slower washout than adenomas. It should be noted that the appearance of adrenal metastasis can be very variable depending on the underlying cancer.
MRI Scans to Evaluate Adrenal Tumors
An MRI demonstrating a left pheochromocytoma (arrow and pathology). Some pheochromocytomas light up brightly on an MRI scan, which is suggestive, but the diagnosis is made by blood or urine metanephrines.
The MRI (also called an MR scan) is very similar to the CT scan in the type of information and pictures it provides. The scan uses magnetic fields to generate pictures of body structures, rather than x-rays like the CT scan or sound waves like the ultrasound, so it involves no radiation. For that reason MRI is preferred in pregnancy and in children, and it is a good alternative when CT contrast cannot be given. Many adrenal tumors are also first seen on an MRI done for another reason.
MRI has similar diagnostic accuracy to CT in characterizing adenomas. On T2-weighted MR images (fluid-filled tissues appear bright), adrenal adenomas are homogeneous and present intermediate-low signal intensity compared to skeletal muscle or liver. An important component of the adrenal MRI protocol is chemical shift imaging (CSI). This modality enables the radiologist to detect fat within the tumor, which shows as a loss of signal intensity. MRI detects nearly all adenomas that measure 10–20 HU on CT, but it is much less reliable for lipid-poor adenomas measuring more than 30 HU.Some pheochromocytomas light up brightly on an MRI scan. This can be suggestive, but the diagnosis is made by blood or urine tests: every patient needs measurement of plasma free metanephrines or 24-hour urine fractionated metanephrines, and must be appropriately prepared prior to adrenalectomy.
MRI showing an adrenal cancer (arrow) arising from the right adrenal gland. Note the heterogeneity and irregular borders.
On MR, adrenocortical carcinomas show low signal intensity on T1-weighted images, high signal on T2-weighted images, and strong and heterogeneous contrast enhancement with slow washout. Similarly, metastasis to the adrenal gland can appear very variable on an MRI scan.
Are Nuclear Medicine Scans Useful For Evaluating Adrenal Tumors?
A nuclear medicine scan uses radioactive substances (a very low radiation dose) to take pictures of areas inside the body. The radioactive substance is injected into the body, and locates and binds to specific cells or tissues, including cancer cells. The technology is similar to a radioactive iodine scan used in thyroid disease, or a sestamibi scan used in parathyroid disease.
A nuclear medicine scan is only needed for certain cases of adrenal tumors, when CT and MRI scans are not sufficient. The most commonly used nuclear imaging scans in adrenal tumor imaging are:
- DOTATATE PET (Gallium-68 DOTATATE PET/CT)
- Regular PET (18-FDG-PET/CT)
- MIBG (I-123 MIBG)
An MIBG scan demonstrating positive uptake in the right adrenal gland (arrow) proving to be a pheochromocytoma.
The MIBG scan is used only to detect the presence and location of pheochromocytomas and paragangliomas (also known as extra-adrenal pheochromocytomas). This test does not detect any other type of adrenal tumor. MIBG is a nuclear medicine scan which takes advantage of the fact that endocrine cells make hormones. A radioactive tracer (I-123 MIBG), which resembles norepinephrine (noradrenaline, a hormone made by the adrenal medulla), is given to the patient. The tracer is concentrated in the hyperactive endocrine tissue which makes up the pheo, and it is then imaged with a special camera. MIBG scintigraphy was for many years the standard functional scan for pheochromocytoma and paraganglioma, but it suffers from drawbacks like limited spatial resolution, difficulty in detecting small tumors (< 1.5–2.0 cm) or large tumors with extensive necrosis or hemorrhage, lack of tracer uptake in some tumors, and interference by certain medications, leading to false-negative results. Today its main role is to select patients with metastatic disease who may benefit from MIBG therapy, or to serve when DOTATATE PET is not available.
What PET Scans are Used to Evaluate Adrenal Tumors and Growths?
A Gallium-68 DOTATATE PET/CT scan for metastatic pheochromocytoma demonstrating multiple metastatic lesions in bone and lymph nodes (arrows).
Pheochromocytoma and paraganglioma cells carry somatostatin receptors on their surface, which allows targeted PET imaging with Gallium-68 DOTATATE. DOTATATE PET/CT shows these tumors with greater contrast against the surrounding tissues than FDG PET/CT, and it is now the first-line functional scan for imaging pheochromocytoma and paraganglioma when such a scan is needed. Depending on the DOTATATE findings and the clinical question, FDG PET and MIBG remain useful in selected cases, and may help with staging, disease characterization and treatment choices.
Regular PET (18-FDG-PET/CT) is mainly used to image malignant (cancerous) lesions, and it is one option for an adrenal tumor that remains indeterminate on CT. It is not perfect: some benign adenomas and pheochromocytomas also take up the tracer. It is an imaging modality which is very useful in adrenocortical carcinoma and metastasis to the adrenal gland (most commonly carcinomas of the lung, breast, kidney, and melanoma). In adrenocortical cancer, 18-FDG-PET/CT can be more accurate than a CT scan and may identify metastasis (spread) for instance to lymph nodes and the liver not detected on the CT scan.
As a functional imaging modality, 18-FDG-PET/CT, which provides glucose metabolic information on malignant tumors, has shown great results for the detection of adrenal metastases. It is used in many cancer patients (including lung, breast, kidney, colorectal cancer and melanoma) and provides information for diagnosis, surveillance, and follow-up after therapy in these cases. Occasionally, an adrenal metastasis is the only evidence of cancer, and in those cases an adrenalectomy may be indicated. Learn more about adrenal surgery for metastasis here.
Ultrasound to Evaluate Adrenal Tumors and Growths
Ultrasound is the fastest, cheapest, and most readily available scan to look at the kidneys and adrenal glands. However, it is the least accurate, so in adults it is not used to examine adrenal tumors. It has a role in newborns and small children.
Last updated October 2026.