How is pheochromocytoma diagnosed?
Pheochromocytoma can be diagnosed based on a number of factors, including a physical examination; blood and urine lab tests, which measure urinary catecholamines and epinephrine and norepinephrine in blood and urine; and imaging, including magnetic resonance imaging (MRI). A CT scan uses ultrafast electron beams to produce three-dimensional views
of organs. It is performed at a hospital or clinic and takes only minutes. An MRI is a computerized scanning method that uses radio waves and a magnet to scan body parts. An MRI is usually performed at a hospital and takes about 30 minutes. There is also a radionucleide scan that can help localized pheochrocytones that are not in the usual gland location. This is metarodobenzylguanidine (MIBG) with I123 (iodine isotope).
The diagnosis of pheochromocytoma is established by the demonstration of elevated 24-hour urinary excretion of free catecholamines (norepinephrine and epinephrine) or catecholamine metabolites (vanillylmandelic acid and total metanephrines). The measurement of plasma catecholamines can also be of value in the diagnosis of pheochromocytoma. However, the measurement of plasma catecholamines has limited sensitivity and specificity. Plasma metanephrines have been reported to be more sensitive than plasma catecholamines. When 52 patients with pheochromocytoma were studied, every patient was found to have elevated plasma levels of metanephrines, but 8 had normal levels of plasma catecholamines. Pharmacologic testing with agents such as glucagon or clonidine is rarely required to make the diagnosis.
Once a person has been diagnosed with a pheochromocytoma, he or she will undergo tests to identify exactly where in the body the tumor is located. The imaging techniques used are usually computed tomography scan (CT scan) and magnetic resonsance imaging (MRI). A CT scan creates pictures of the interior of the body from computer-analyzed differences in x rays passing through the body. CT scans are performed at a hospital or clinic and take only a few minutes. An MRI is a computerized scanning method that creates pictures of the interior of the body using radio waves and a magnet. An MRI is usually performed at a hospital and takes about 30 minutes.