The parathyroid glands are four small glands typically situated behind the thyroid gland in the neck. These organs produce parathyroid hormone (PTH), which acts as the body’s primary regulator of calcium levels in the blood and bones. A parathyroid scan, often a nuclear medicine test, is a specialized diagnostic tool used when these glands are suspected of functioning improperly. This procedure helps medical professionals locate the specific gland or glands that may be causing a calcium imbalance.
Why the Parathyroid Scan is Necessary
The parathyroid scan is primarily used to investigate a condition called hyperparathyroidism, where one or more glands become overactive and produce too much PTH. This hormonal excess leads to elevated calcium levels in the bloodstream, which can affect the bones, kidneys, and nervous system over time. Pinpointing the exact position of the abnormal tissue is crucial before surgery.
The scan uses a radioactive tracer called Technetium-99m Sestamibi, which is injected into the patient’s vein. This tracer is readily absorbed by cells with high metabolic activity, including both the thyroid gland and any overactive parathyroid tissue, such as an adenoma. The imaging relies on a differential washout mechanism that occurs over time. While the tracer is quickly cleared from the normal thyroid tissue, the abnormal parathyroid tissue retains the tracer for a much longer period. This difference in tracer retention allows the imaging equipment to clearly distinguish the problematic gland from the surrounding healthy structures.
Preparation and What to Expect Beforehand
Patient preparation for this scan generally focuses on ensuring the best possible image quality and safety. Patients are often asked about any recent medical procedures, such as a CT scan involving iodine contrast, as these substances can interfere with the results. You will typically be instructed to wear comfortable clothing without metal fasteners, and you will need to remove all jewelry from around your neck and chest area before the procedure begins.
Though some centers allow for a normal diet, you may be asked to fast or limit certain medications that could influence your thyroid or calcium levels, so following specific instructions from your clinic is important. The scan often spans several hours, including lengthy waiting periods between imaging sessions. Preparing for a long appointment, perhaps by bringing reading material, can make the process easier.
The Parathyroid Imaging Procedure
The procedure begins with the intravenous injection of the Technetium-99m Sestamibi radiotracer, usually into a vein in your arm or hand. This allows the tracer to circulate and be absorbed by the glands. This is followed by the initial imaging session, where you will lie still on an examination table while a specialized device called a gamma camera takes pictures of your neck and upper chest.
These first images, known as the early phase, show tracer uptake in both the thyroid and any hyperactive parathyroid tissue. The patient is then released for a longer waiting period, typically between one and three hours, during which the differential washout occurs. Sometimes, the technologist may use Single-Photon Emission Computed Tomography (SPECT) imaging, which rotates around your body to create detailed, three-dimensional images of the tracer distribution. This advanced technique, often combined with a low-dose CT scan (SPECT/CT), provides better anatomical context and more precise localization, especially for glands located in unusual positions.
What the Scan Results Reveal
The final images are interpreted by comparing the early and delayed scans to identify areas of persistent radiotracer activity. An abnormal parathyroid gland, such as an adenoma, will be clearly visible as a “hot spot” that has retained the tracer, while the normal thyroid tissue has cleared it. This retained activity indicates the location of the overactive tissue responsible for the elevated PTH levels.
The precise localization provided by the parathyroid scan is instrumental for surgical planning, allowing surgeons to perform a minimally invasive parathyroidectomy. This targeted approach results in a smaller incision, a shorter operating time, and a quicker recovery for the patient. The amount of radiation exposure from the tracer is very low, comparable to a standard chest X-ray. You will be encouraged to drink plenty of fluids after the scan to help flush the radiotracer from your body more quickly.