Parathyroid Scan

Definition

A parathyroid scan is a nuclear medicine procedure that uses a small amout of radioactive material to create an image of the parathyroid.

Purpose

A parathyroid scan is used to help detect and diagnose problems with the parathyroid. It is used to help diagnose parathyroid cancer , a uncommon and slow growing cancer, but one that can be deadly when it spreads, or metastizes to other areas of the body or causes very high levels of calcium in the blood, known as hypercalcemia. A parathyroid scan is also used to help diagnose over activity of the parathyroid, known as hyperparathyroidism.

Precautions

Women who are pregnant should not have a parathyroid scan. Only very small amounts of radioactive tracer are used in the proceedure, which have been shown to be safe for adults. However, the radioactive tracer can pass into the fetus from the mother's bloodstream, and it is not completely clear what effects even small amounts of radioactive material have on a developing fetus. Instead, pregnant women should schedule the scan for after delivery of the baby or use alternative diagnostic and imaging procedures.

Women who are breastfeeding should also not undergo a parathyroid scan because the radioactive material can be passed to the nursing infant in the breast milk. If a breastfeeding woman needs to undergo the scan she should arrange alternative feeding

QUESTIONS TO ASK YOUR DOCTOR

If the scan shows abnormalities in my parathyroid, what is the next step?
How likely is a false positive? A false negative?
What other diagnostic or imaging procedures might be appropriate for me?

methods for the day following the scan and the following two to three days until the radioactive tracer has been eliminated from her body.

The quality of the parathyroid scan image can be negatively affected by the presence of barium or bismuth in the individual's body. Barium is used in some imaging procedures as a contrast material. Any procedures involving barium should be scheduled for at least four days before the scan, or after the parathyroid scan has been completed. Bismuth is a component of some medicines used to treat nausea, diarrhea , upset stomach, and heartburn . It is sold under a variety of brand names including Pepto-Bismol. No medicine containing bismuth should be taken for four days before the scan.

Description

A parathyroid scan uses very small amounts of radioactive material to create an image of the parathyroid. The parathyroid is actually not one thing, but rather the collection of four organs, each about the size of a pea, that are located in the neck near the thyroid. The parathyroid's main function is to release parathyroid hormone (PTH) into the body. This helps to regulate the levels of calcium in the blood and the amount of calcium that the body stores.

The first step of a parathyroid scan is to inject the radioactive material, sometimes called a radioactive trace or simply a trace. The trace is usually injected in the patient's arm. The trace enters the bloodstream directly, where it circulates throughout the body. Some of it is absorbed by the parathyroid. The trace emits very low levels of gamma radiation. This radiation can be detected by a specialized device called a gamma camera. The gamma camera is sensitive to the gamma radiation and passes that information to a computer which uses the information to create an image of the parathyroid and the surrounding area.

After the trace has been injected the scan can begin. In some cases the scan is started immediately after the injection. In other cases the patient may be asked to wait for a certain amount of time to allow the trace to be absorbed into the parathyroid.

The patient is placed onto a table with his or her head stabilized while the gamma camera moves around the patient to image the parathyroid from a variety of angles. It is important for the patient to lie extremely still during the imaging, because any movement can cause the image to be blurry and unreadable. The patient may be asked to hold his or her breath for short times during the scan to help ensure a clear image. The nuclear medicine technician doing the scan may reposition the patient a number of times to allow the parathyroid to be imaged from different angles.

The parathyroid may be imaged, and the patient asked to wait for a certain period of time and then imaged again. In many cases the parathyroid is scanned at one and two hours after injection of the trace. In between the patient is free to move around. The patient may be asked to drink water to help flush any trace not absorbed by the parathyroid from the body.

Preparation

For most individuals, no special preparation is required before the individual arrives for the appointment. However, women who are breastfeeding may be asked to switch to an alternative feeding method before the scan. Before the scan, the individual will be asked to remove all metal jewelry and accessories, and may be asked to put on a gown.

Aftercare

So special aftercare is required. Individuals can go about their normal activities immediately after the scan is complete. However, women who are breast feeding should not resume breast feeding until at least a few days after the proceedure to ensure that all of the radioactive tracer has been eliminated from the body and will not be passed to the nursing infant.

Complications

Most individuals experience no complications from a parathyroid scan. There is a small risk of bleeding, bruising , swelling, or infection any time an injection is given. In extremely rare cases the radioactive tracer may cause an allergic reaction.

KEY TERMS

gamma radiation —High-energy, short wavelength electromagnetic radiation emitted by the nuclei of an excited atom.

Results

A diagnosis is not made on the basis of a parathyroid scan alone. Instead, information from other diagnostic tests is combined with information about symptoms, health history , physical examination, and risk factors, to make an accurate diagnosis. However, a parathyroid scan can provide extremely valuable information about the presence of a problem and its location.

A normal parathyroid scan shows the same amount of the radioactive tracer being absorbed in all areas of the parathyroid. An abnormal scan, in contrast, shows that one or more areas of the parathyroid are absorbing abnormally large amounts of the tracer. This indicates increased levels of parathyroid activity in that location which may be caused by a tumor.

Caregiver concerns

A doctor determines the need for a parathyroid scan. The doctor, a nurse, or a nuclear medicine specialist explains the proceedure to the patient and answers any questions or concerns about the proceedure that the patient may have. A nurse gives the injection of the radioactive tracer. A nuclear medicine technician or nuclear medicine technologist performs the scan. The images that result from the scan are then interpreted by a radiologist or a doctor specializing in nuclear medicine. The results are then communicated to the doctor who ordered the scan who then informs the patient of the results and determines which if any additional diagnostic tests or treatments are necessary.

Resources

BOOKS

Brant, William E. and Clyde A. Helms. Fundamentals of Diagnostic Radiology, 3rd Ed. Philadelphia: Lippincott, Williams & Wilkins, 2007.

Naveh-Many, Tally, ed. Molecular Biology of the Parathyroid. New York: Kluwer Academic/Plenum, 2005.

Shannon, Joyce Brennfleck. Endocrine and Metabolic Disorders Sourcebook, 2nd Ed. Detroit, MI: Omnigraphics, 2007.

PERIODICALS

“Recent Advances in Thyroid Cancer.” Current Problems in Surgery 45.3 (March 2008): p.156–251.

Demir, Hakan, Metin Halac, Gozde D. Gorur, Kerim Sonmezoglu and Ilhami Uslu. “FDG PET/CT Findings in Primary Hyperparathyroidism Mimicking Multiple Bone Metastases.” European Journal of Nuclear Medicine and Molecular Imaging 35.3 (March 2008): 686–687.

ORGANIZATIONS

Radiological Society of North America, 820 Jorie Blvd, Oak Brook, IL, 60523-2251, 800-381-6660, http://www.rsna.org/.

Robert Bockstiegel