Adrenal medullary imaging

Alternative names
MIBG (iodine-131-meta-iodobenzylguanidine) scintiscan

Definition
This is a nuclear scan test that uses injected radioactive material (radioisotope) and a special scanner to locate or confirm pheochromocytoma (an adrenal gland tumor).

How the test is performed
A radioisotope (MIBG, iodine-131-meta-iodobenzylguanidine) is injected into a vein. Later that day (or the next day) you are asked to lie on a table which is placed under the arm of the scanner. The abdomen is scanned. You may be asked to return for repeated scans for 1 to 3 days. Each scan takes 1 to 2 hours.

After injection of the radioisotope, you are given Lugol’s iodine solution to block uptake into the thyroid. Because the radiation from this radioisotope is fairly high compared to most other radioisotopes, some precautions may be necessary for a few days after the test. The nuclear medicine personnel will instruct about specific precautions, which may include flushing the toilet twice after each use (to dilute radioactive material excreted in the urine) or other precautions.

How to prepare for the test
Lugol’s iodine solution may be given before the test as well as after administration of the radioisotope.

You must sign an informed consent form.

A hospital gown is usually worn during the scan, although loose fitting clothing may be allowed. Remove jewelry or metal objects before each scan.

For infants and children:
The preparation you can provide for this test depends on your child’s age and previous experience. For specific information regarding how you can prepare your child, see the following topics:

How the test will feel
There is a sharp needle prick when the material is injected. The radioisotope is not felt by the body, and the scan causes no sensation, but the table may be cold or hard. You must lie still during the scan.

Why the test is performed
To confirm pheochromocytoma, particularly when a CT scan is negative or inconclusive, or if multiple tumors or an extra-adrenal (not within the adrenal gland) tumor is suspected.

Normal Values

Normal values indicate localized areas of increased uptake of the radioisotope.

What abnormal results mean

Most often, this test is used to locate pheochromocytoma. It may be particularly useful to detect multiple tumors or tumors that are located in extra-adrenal tissues.

Additional conditions under which the test may be performed:

     
  • Multiple endocrine neoplasia (MEN) II

What the risks are


The risks are essentially the same as for X-rays (radiation) and for needle pricks.

There is some exposure to radiation from the radioisotope. The radioisotope contains iodine, so precautions (such as administration of Lugol’s solution) are used to prevent excessive uptake by the thyroid. There is significant exposure of the adrenal gland to radiation.

This test should not be performed on pregnant women because of the danger to the fetus from radiation.

Any time the body is penetrated (such as with a needlestick), there is a risk of infection. Injection into a vein also carries a slight risk of bleeding. The risk is no greater for this scan than for intravenous injection of any sort.

Special considerations

The radioisotope is costly and may not be available in all medical facilities. The person must be able to return for delayed images (1 to 3 days).

Johns Hopkins patient information

Last revised: December 7, 2012
by Mamikon Bozoyan, M.D.

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