CT, MRI and PET Scans for Pheochromocytoma

Which Scans Are Used for Pheochromocytoma of the Adrenal Gland (and Paraganglioma)?

Doctors have a number of options when they order scans to look for a pheochromocytoma within the adrenal gland. These imaging choices include CT scans, MRI scans, nuclear medicine scans (DOTATATE PET, MIBG, FDG PET) and ultrasound. The scan should always be read together with the blood or urine metanephrine tests and the whole picture of the patient. We carefully analyze the imaging phenotype of the tumor. The imaging phenotype describes all the aspects of what the tumor looks like on your scan and helps us arrive at the correct diagnosis. It should be noted that this is far from a perfect science. No scan can tell whether a pheochromocytoma will ever spread (metastasize); a scan can only show whether it already has. A suspected pheochromocytoma should not be biopsied with a needle.

What Do Adrenal Experts Look for on Scans of a Pheochromocytoma?

Experts at adrenal surgery look for several characteristics of tumors on the different imaging studies (scans). In fact, we look at 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: whether the borders are smooth or irregular, and whether the margins are clear or unclear.

The most important points about scans for pheochromocytomas are:

• A benign cortical adenoma is the most common adrenal tumor, and it is almost always round. A cortical adenoma grows from the adrenal cortex, the outer layer of the adrenal gland (see adrenal anatomy). Most adenomas are rich in fat and measure 10 Hounsfield units (HU) or less on a CT without contrast. A pheochromocytoma is essentially never that low, so a density of 10 HU or less makes a pheochromocytoma very unlikely.
• CT or MRI is used to find the tumor. For most adults a CT scan is the first scan, and often the only scan, that is needed. In our experience an “adrenal-protocol” CT, done without and with IV contrast, gives the most information.
• For most adults, MRI adds little to a good CT. MRI is the appropriate first scan in children and in pregnancy, because it uses no radiation.
• Functional (nuclear medicine) imaging is not needed for a typical single pheochromocytoma in one adrenal gland. It is used when metastatic, multifocal or hereditary disease is suspected. A 68Ga-DOTATATE PET scan is generally preferred; an I-123 MIBG scan is an alternative, particularly when MIBG therapy is being considered.
• Ultrasound cannot characterize adrenal tumors in adults and is not needed.

CT Scans (CAT Scans) for Pheochromocytoma and Other Adrenal Masses

The CT scan (also called CAT scan) is very accurate at examining the adrenal glands and other abdominal structures and can be used for any type of adrenal tumor. The CT scan is painless and takes only a few minutes to complete. The pictures are very good at finding tumors, and very accurate measurements can be taken, which helps in planning treatment. CT is the first-level imaging test for adrenal masses because it is quick and has high spatial resolution; the appearance before contrast and the behavior after contrast are both used to reach a diagnosis.

The “adrenal-protocol, contrast-enhanced CT scan” is our preferred scan for adrenal tumors and masses. The unenhanced part (before IV contrast is given) provides the single most useful number, the density of the tumor, and the contrast part adds detail about the tumor and the structures around it. Modern IV contrast is safe for patients with a pheochromocytoma. On CT scans, adrenal adenomas are usually well-demarcated round or oval lesions, with homogeneous and relatively low attenuation values (10 Hounsfield Units [HU] or lower), due to high fat content. Unfortunately, unenhanced (non-contrast) CT alone is not always diagnostic, since 15–30% of adenomas are lipid-poor and show higher attenuation values, like pheochromocytomas do. This is one reason a pheochromocytoma, especially a small, silent one, can be mistaken for an adenoma on a scan, and why every adrenal mass needs metanephrine testing.

MRI Scans for Pheochromocytoma (or Paraganglioma)

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 takes longer than a CT and uses magnetic fields to generate pictures of body structures, rather than x-rays like the CT scan or sound waves like the ultrasound. Because it involves no radiation, MRI is the appropriate first scan for children and for pregnant women, and it is often used for the repeated, lifelong surveillance scans of people who carry a hereditary gene change.

MRI has similar diagnostic accuracy to CT. On T2-weighted MR images (on which fluid-filled tissues appear bright), adrenal adenomas are homogeneous and have intermediate-to-low signal intensity compared to skeletal muscle or liver. An important component of an adrenal MRI protocol is chemical shift imaging (CSI), which enables the radiologist to detect fat inside the tumor as a loss of signal intensity. MRI detects lipid-rich adenomas very reliably, but its sensitivity for lipid-poor adenomas is considerably lower.

Some pheochromocytomas light up brightly on T2-weighted MRI images. This appearance is suggestive, but it is seen in only some pheochromocytomas and it does not by itself make the diagnosis. Pheochromocytoma patients always need measurement of plasma or 24-hour urine fractionated metanephrines and must be appropriately prepared prior to adrenalectomy.

Nuclear Medicine Scans for Pheochromocytoma and Paraganglioma: DOTATATE PET and MIBG

A nuclear medicine scan (also called functional imaging) uses a small dose of a radioactive substance 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 tumor 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 needed only in certain cases: when a pheochromocytoma or paraganglioma is suspected to have spread (metastatic disease), when there may be more than one tumor (multifocal disease), in hereditary disease, and for paragangliomas. A typical single pheochromocytoma in one adrenal gland, with clear blood tests and a good CT or MRI, does not need one. The nuclear medicine scans used are DOTATATE PET (68Ga-DOTATATE PET/CT), MIBG (I-123 MIBG), and regular PET (18-FDG-PET/CT).

The DOTATATE PET scan is generally the preferred functional scan for pheochromocytoma and paraganglioma. It detects somatostatin receptors on the surface of pheochromocytoma and paraganglioma cells, using PET imaging with 68Ga-DOTATATE. It produces sharp images with strong contrast between the tumor and the surrounding tissues, and it is particularly good at finding paragangliomas, metastases and multiple tumors. Depending on the DOTATATE findings and the clinical question, MIBG and FDG PET remain useful in selected cases and may help with staging and treatment choices.

The MIBG scan detects only pheochromocytomas and paragangliomas (remember, paragangliomas are closely related tumors that grow outside the adrenal gland) and a few related tumors. MIBG is a substance that resembles norepinephrine (noradrenaline), one of the hormones made by the adrenal medulla, so it is taken up and concentrated by pheochromocytoma cells. For imaging it is labeled with radioactive iodine-123 (I-123 MIBG), and the pictures are taken with a special camera, usually the day after the injection. MIBG is an alternative to DOTATATE PET, and it is particularly useful when treatment with MIBG is being considered for metastatic disease, because the scan shows whether the tumors take it up. Its drawbacks are limited spatial resolution, difficulty in detecting small tumors or large tumors with extensive necrosis or hemorrhage, lack of uptake in some tumors, and interference from certain medications, all of which can lead to false-negative results.

FDG PET Scans for Pheochromocytoma and Paraganglioma

Regular PET (18-FDG-PET/CT) shows how much glucose (sugar) a tumor uses and is mainly used to image cancers. In pheochromocytoma and paraganglioma it can be useful in metastatic disease, particularly in people with a change in the SDHB gene. It is also very useful in adrenocortical carcinoma and in metastasis to the adrenal gland from other cancers (most commonly carcinomas of the lung, breast and kidney, and melanoma), where it may identify spread, for instance to lymph nodes and the liver, that is not detected on the CT scan.

18-FDG-PET/CT is used in many cancer patients (including lung, breast, kidney and colorectal cancer and melanoma) for diagnosis, surveillance, and follow-up after therapy. 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.

Is Ultrasound Helpful for Pheochromocytoma or Paraganglioma?

Ultrasound is the fastest, cheapest, and most readily available scan to look at the kidneys and adrenal glands, but it is the least accurate. It cannot characterize adrenal tumors in adults, so it is not needed and it does not replace a CT or MRI.

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For clinicians: the next three paragraphs are technical. We include them for the referring doctors who read this page. If you are not a doctor, don't worry about this section.

The absolute percentage washout (APW) of contrast from the adrenal tumor can be calculated using a formula. The relative percentage washout (RPW) is used when an unenhanced CT value is not available. Classically, an APW >60% or RPW >40% 15 minutes after contrast administration has been taken to indicate a benign adenoma. Washout calculations are relied on less today than they used to be.

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, pheochromocytomas and metastases, which typically demonstrate strong enhancement but prolonged washout.

Pheochromocytomas on Contrast-Enhanced CT Scans. Pheos can present with solid, cystic, calcific, and/or necrotic components, and are quite variable. Smaller pheos tend to display a more uniform attenuation, with an unenhanced density well above 10 HU. After contrast administration, pheochromocytomas enhance avidly (meaning they turn very bright), some more on the portal venous phase and others on the arterial phase; nevertheless, their APW and RPW can be similar to those of adenomas. Therefore, pheochromocytomas cannot be reliably differentiated from adenomas using CT washout protocols, and biochemical testing with metanephrines is required for every adrenal mass. When lesions are large, hemorrhage, necrosis, or calcifications within the tumor can be observed.

Last updated October 2026.

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