Parathyroid scintigraphy is a specialized imaging test that utilizes a small amount of radioactive material to create pictures of the parathyroid glands. This non-invasive procedure helps medical professionals examine how these glands are functioning. The primary purpose of this scan is to pinpoint the exact location of parathyroid tissue that may be overactive or situated in an unusual position within the body.
Why Parathyroid Scintigraphy is Performed
The main reason for performing a parathyroid scintigraphy scan is to locate overactive parathyroid glands, which are typically four small glands situated near or behind the thyroid gland in the neck. These glands produce parathyroid hormone (PTH), which plays an important role in regulating calcium levels in the blood and bones. When one or more of these glands become overactive, it leads to a condition called hyperparathyroidism, causing elevated calcium levels in the bloodstream.
The scan helps identify the precise location of an adenoma, which is a benign tumor, or parathyroid hyperplasia, a condition where all four glands are enlarged. Pinpointing the exact site of the problem gland or glands is important for surgical planning. This specificity allows surgeons to perform a more targeted and less invasive procedure, making the surgery easier and potentially shortening recovery time.
Preparing for the Scan
Specific instructions are provided to patients preparing for a parathyroid scintigraphy scan, though some facilities may have no special preparation requirements. Patients may be advised to avoid certain medications, such as vitamin D supplements, and should discuss all current medications, including over-the-counter drugs, with their healthcare provider. It is recommended to remove any metal jewelry or accessories from the neck area before the scan, and wearing loose-fitting, comfortable clothing is recommended.
Patients should inform the medical team about any allergies or pregnancy, as radiation exposure is not suitable for pregnant women. For breastfeeding mothers, special preparations may be necessary, sometimes involving a temporary interruption of breastfeeding. While some facilities allow normal eating and drinking, it is always best to confirm any dietary restrictions with the nuclear medicine department prior to the appointment.
The Scintigraphy Procedure
The parathyroid scintigraphy procedure begins with the injection of a radioactive tracer, such as technetium-99m sestamibi, into a vein in the arm or hand. This tracer is designed to be absorbed by overactive parathyroid tissue more readily than by healthy glands. After the injection, there is a waiting period of about 15 minutes to allow the tracer to circulate and be taken up by the parathyroid glands.
Following this initial waiting period, the patient lies on a scanning bed, often with a support under the shoulders to extend the neck, making the area more accessible for imaging. A gamma camera is then used to capture early images of the neck and chest area. These images take about 30 minutes to acquire.
After the early imaging, there are delayed scans. Patients may be asked to return to the department after one to two hours for a second set of images. The entire test can take about four hours to complete.
Understanding the Scan Results
The images produced during parathyroid scintigraphy reveal areas where the radioactive tracer has accumulated. Overactive parathyroid tissue, such as an adenoma or hyperplastic glands, absorbs and retains the tracer more than normal tissue, making these areas appear as “hot spots” on the scan.
The scan helps identify common findings, including a single adenoma, multiple adenomas, or generalized hyperplasia affecting all four glands. The scan can also detect ectopic parathyroid tissue, which is located away from its usual position. The information gained from these images provides medical professionals with anatomical and functional details, guiding subsequent treatment decisions, particularly surgical removal of the identified overactive gland or glands.
Safety and Potential Considerations
Parathyroid scintigraphy involves exposure to a small amount of radiation, similar to that from other common diagnostic imaging procedures. The radioactive tracer used emits gamma rays that are comparable to X-rays. The radiation dose is considered low, and the tracer naturally decays and is eliminated from the body within two days.
Allergic reactions to the radioactive tracer are rare. Medical professionals weigh the risks against the benefits of the scan, which provides valuable information for diagnosing and treating parathyroid conditions. The diagnostic insights gained outweigh any risks associated with the small radiation dose. Patients are advised to avoid close contact with small children for a short period after the scan due to the radioactivity released.