Pheochromocytoma (adrenaline-producing adrenal tumor)
Diagnosis and Radiological Tests
In patients who are thought to have a pheochromocytomaPheochromocytoma - a disease where too much adrenaline is being made by an adrenal tumor, biochemical tests should be done to measure the levels of catecholamines (adrenalineAdrenaline - the hormone that helps control the "fight or flight" response and puts the body on "high alert" (also known as epinephrine), noradrenaline, and dopamine) and metanephrines (i.e. the molecules that catecholamines break down into). The reason that many physicians rely on the metanephrines levels more than the catecholamine levels is that adrenaline only lasts a short time in the body before it is broken down where metanephrines last much longer in the body. Catecholamine and metanephrines levels may be measured in either the plasma (i.e. blood) or in a 24 hour urine collection. It is not clear if the urine test or the blood test is "better" so you should work with your physician to determine which is better for you. In general, plasma tests are better for children with whom a 24 hour urine collection is not possible. In addition, plasma metanephrines is a very sensitive study (i.e. identifies all patients with the disease, but may have false positivesi.e. positive test in someone who does not have a pheochromocytoma) and is therefore good for patients with known disease and for patients with a known family history of pheochromocytoma or associated genetic syndromes. Although the NIH recommends plasma metanephrines for patients with an incidentally discovered adrenal tumor, many physicians feel that the 24 hour urine test is better than the plasma test because it has fewer false positives. Levels that are at least twice the upper limit of normal levels confirm that the patient has a pheochromocytoma. For patients with an adrenal incidentalomaAdrenal incidentaloma - an asymptomatic adrenal tumor that is discovered on an imaging test (CAT scan, MRI, etc) which was ordered to evaluate a problem that is unrelated to adrenal disease., if the metanephrines levels are between 1 and 2 times the upper limit of normal, there is an approximately 30% risk of pheochromocytoma.8 Certain medications and certain conditions can lead to false positive results (i.e. a positive test in someone who does not have pheochromocytoma:
- Tricyclic antidepressants (including cyclobenzaprine hydrochloride)
- Ethanol (alcohol) withdrawal
- Withdrawal from clonidine and other drugs (e.g., elicit drugs)
- Antipsychotics, buspirone hydrochloride, and bupropion hydrochloride
- Major physical stress (e.g., surgery, stroke)
- Obstructive sleep apnea syndrome
Check with your doctor before being tested and be sure he or she knows all of your medications. Other available tests include suppression and provocative testing that are rarely, if ever, needed. Provocative tests can cause life-threatening high blood pressure.
Figure 8: Pheochromocytoma On CAT scan
Figure 9: Pheochromocytoma On MRI
Figure 10: Metastatic Pheochromocytoma On MIBG scan
When the diagnosis is confirmed with plasma or urine studies, the patient should have a CAT scan or MRI to identify the location of the pheochromocytoma. Pheochromocytomas usually have a very distinct appearance on CAT scan and MRI. CT or MRI can also help determine if other organs are involved or other tumors outside the adrenal glands (i.e. paragangliomas) exist.
When the adrenal glands appear normal or near-normal on CAT scan or MRI, nuclear medicine tests like an MIBG scan (i.e. metaiodobenzylguanidine scan) or PET scan (i.e. positron emission tomography scan) can be helpful. These tests use a weakly radioactive particle to home into the tumor so that it "lights up" on X-ray. The MIBG scan is specific for adrenaline-producing tumors while the PET scan identifies any very metabolically active tumors. Radioisotope scans may also be useful in detecting small paragangliomas, metastatic disease, and subtle areas of recurrent disease. They are also useful in screening patients with familial disorders where bilaterality and extra-adrenal pheochromocytomas (paragangliomas) are more common.