What X-Rays and Scans are Best for Pheochromocytoma of the Adrenal Gland (and Paraganlioma Within the Abdomen?

Doctors have a number of options when they order scans or x-rays to look for the presence of a pheochromocytoma within the adrenal gland. These imaging choices include: Ultrasound, CT scans, MRI scans and Nuclear Medicine scans (MIBG, PET scans, etc). It is best of the doctor approaches this with a whole-person approach in order to evaluate all aspects of the tumor and 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 as the correct diagnosis including the likelihood of cancer. It should be noted, this is far from perfect science. In many cases we can never know for sure whether the tumor is cancerous short of removing it via an adrenal operation. But an expert at adrenal surgery (there are very few expert adrenal surgeons) should be able to tell fairly accurately if a tumor is cancerous prior to operating.

What do the Expert Adrenal Doctors Look for on the Adrenal X-Rays and Scans Obtained to Look at Pheochromocytomas?

Experts at adrenal surgery look for several characteristics of tumors that are seen on the different imaging studies (scan), in fact, we look at a combination of more than a dozen of 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.

The key and most important points of adrenal imaging and adrenal scans for pheochromocytomas are:

  • A benign cortical adenoma is the most common adrenal tumor and they are almost always round. A cortical adenoma is an adrenal tumor that growes from the adrenal cortex -- the outermost layer of the adrenal gland. (see adrenal anatomy for more info).
  • The gold standard of adrenal imaging is a CT scan (CAT scan). An “adrenal-protocol, contrast enhancement CT scan” is best. Thus a CT Scan of the adrenal with and without contrast should always be the first scan ordered, and in more than 90% of cases the ONLY scan a patient will need.
  • MRI scans are almost never necessary and should never be the first scan that a doctor orders to look at adrenal masses.
  • Nuclear medicine scans are almost never necessary. Nuclear medicine is helpful in some very specific settings that few doctors will ever see.
  • Ultrasound is not very helpful, so don't bother getting an ultrasound. If you get one and you become our patient, we won't look at the ulrasound because it won't give useful information.

CT Scans (CAT Scans) to Evaluate Pheochromocytoma Tumors and Masses Within the Adrenal Gland

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 3 tests in this group, the CT scan is painless. It will take only a few minutes to complete. The pictures which result are very good at finding tumors throughout the body, and very accurate measurements can be taken which help the planning of subsequent therapies. CT represents the first-level imaging modality for the evaluation of adrenal lesions, since it permits a quick execution ensuring high spatial resolution, with findings of pre-contrast images and post-contrast behavior being commonly used to achieve a correct diagnosis.

The “adrenal-protocol, contrast enhanced CT scan” is the best scan or x-ray for adrenal tumors and masses. An unenhanced (no IV contrast is given to the patient) is good, but not nearly as good as a CT WITH IV contrast. On CT scans, adrenal adenomas are usually well-demarcated round or oval lesions, with homogeneous and relatively low attenuation values (lower than 10 Hounsfield Units [HU]), due to high fat content. 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 (adrenal-protocol, contrast enhancement CT scan) is required to differentiate adenoma from non-adenomas. The evaluation of the enhancement pattern of adrenal lesions needs a further late phase after the acquisition of the venous phase. There are different CT protocols suggested for the evaluation of adrenal masses; however, there is evidence that a 15-min post-contrast protocol has the highest diagnostic accuracy.

Can MRI Scans Help Evaluate and Locate a Pheochromocytoma (or Paraganglioma)?

The MRI (also called an MR scan or NMR scan) is very similar to the CT scan in the type of information and pictures it provides. The scan takes about an hour and uses magnetic fields to generate pictures of body structures rather than x-rays like the CT scan or sound waves like the ultrasound.

MRI has similar diagnostic accuracy to CT allowing characterizing adenomas regardless of their CT enhancement. 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 adrenal MRI protocol is chemical shift imaging (CSI). This modality enables the radiologist to detect intra-tumor fat resulting in a loss of signal intensity. The MR sensitivity for adenomas measuring 10–20 HU is nearly 100%, while that for lipid-poor adenomas measuring greater than 30 HU is significantly lower (13–75%)

Often pheochromocytomas enhance (light up brightly) on an MRI scan which is so characteristic that it by itself clinches the diagnosis. Of course, pheochromocytoma patients still need to have their plasma and urine (24 hour collection) measurements of fractionated metanephrines and catecholamines measured and be appropriately prepared prior to adrenalectomy. On MRI, adrenocortical carcinoma shows 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 to Help Locate and Evaluate Pheochromocytoma or Paraganglioma?

A nuclear medicine scan uses radioactive substances (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 as a radioactive iodine scan used in thyroid disease, or a sestamibi scan used in parathyroid disease. Learn more about these scans here.

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 • MIBG (I-131 MIBG) • DOTATATE PET (Gallium-68 PET/CT) • Regular PET (18-FDG-PET/CT)

The MIBG Scan is used only to detect the presence and location of pheochromocytomas and paragangliomas (remember, paragangliomas are just pheos that don't grow within the adrenal gland -- also known as extra-adrenal or outside-adrenal pheochromocytomas). The MIBG test does NOT detect any other type of adrenal tumor, only pheos. MIBG is another nuclear medicine scan which takes advantage of the fact that endocrine cells make hormones. A special radioactive dye is given to a patient which is a precursor for adrenaline (the hormone made by the adrenal medulla). This dye is concentrated in the hyperactive endocrine tissue which comprises the pheo and it can be seen on x-ray film. MIBG scintigraphy is the functional nuclear medicine imaging of choice for pheochromocytoma and paraganglioma, but suffers from drawbacks like limited spatial resolution, difficulty in detection of small tumors (< 1.5–2.0 cm) or large tumors with extensive necrosis/ hemorrhage, lack of tracer uptake in some tumors, and interference with certain medications, leading to false-negative results.

The DOTATATE scan is a more recent nuclear medicine technology which looks at the presence of somatostatin receptors within pheochromocytoma and paraganglioma cells, which facilitates targeted PET imaging with 68-Ga-DOTA-peptides. a-68 DOTATATE PET/CT detected similar number but has significantly greater lesion-to-background contrast compared to FDG PET/CT. DOTATATE PET/CT should now be considered the ideal first line investigation for imaging pheochromocytoma and paraganglioma. Depending on DOTATATE findings and the clinical question, FDG and MIBG remain useful and, in selected cases, may provide more accurate staging, disease characterization and guide treatment choices

TODO. The picture on the right shows a bright pheo in the patient's left adrenal gland. To make the picture easier to interpret, the radiologist gave the patient a second radioactive dye which is absorbed by the kidney. The computer interprets the dye in both kidneys as black areas, which accounts for the two "empty" areas on the scan. The pheo, therefore is the bright spot (the adrenal) on the top side of the left (empty) kidney. This test takes about an hour a day for 3 or 4 days. Note: X-rays are typically read as if we were looking at the patient, therefore, the patients left side will be on the right side of the picture we are viewing.

Are PET Scans Helpful to Evaluate and Locate Pheochromocytomas or Paragangliomas?

Regular PET (18-FDG-PET/CT) is mainly used to image malignant (cancerous lesions). 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 provided information for diagnosis, surveillance, and following therapy in these cases. Occasionally, an adrenal metastasis is the only evidence of cancer, and in those cases an adrenalectomy is indicted. Learn more about adrenal surgery for metastasis here.

Is Ultrasound Helpful to Evaluate and Locate Pheochromocytomas or Paragangliomas?

Ultrasound is the fastest, cheapest, and most readily available scan to look at the kidneys and adrenal glands. But, it is the least accurate, so it is usually not used as much as the CT scan. It can be used to examine any type of adrenal tumor but it is not very good so don't bother. We don't want to look at ultrasounds of the adrenal gland--it is a waste of our time.

Sorry folks for the technical stuff in the next 3 paragraphs below... this is by far the most technical page of this huge website. We do this because almost every endocrinologist that gets a patient with an adrenal tumor reads this website, so we must throw in some technical stuff for them so they can take better care of you. Don't worry about the technical stuff if you are not a doctor -- keep reading because 95% 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 unenhanced CT value is not available. If the APW is >60% or RPW is >40% after 15-min from contrast administration, this is indicative of benign adenoma, with sensitivity and specificity of 88% and 96% at the APW and sensitivity and specificity of 83% and 93% at the RPW, respectively.

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 instead demonstrate strong enhancement but pro- longed washout.

Pheochromocytomas on Contrast-Enhanced CT Scans. Pheos 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 other 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.

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