The parathyroid scan is a specialized diagnostic tool used in nuclear medicine to evaluate the small glands in the neck that regulate calcium levels in the body. These four glands, usually situated behind the thyroid, produce parathyroid hormone (PTH), which acts as a hormonal thermostat to maintain precise calcium balance in the blood and tissues. A parathyroid scan is primarily performed when blood tests indicate a problem with this calcium regulation system. The procedure utilizes a mild radioactive tracer and specialized cameras to create images that help locate any abnormal glandular tissue.
Why Parathyroid Scans Are Perform
This imaging procedure identifies the location of overactive parathyroid tissue, which causes primary hyperparathyroidism. This disorder occurs when one or more parathyroid glands produce excess parathyroid hormone, regardless of the body’s calcium needs. The resulting high levels of parathyroid hormone cause calcium to be drawn from the bones and preserved by the kidneys, leading to hypercalcemia.
Most primary hyperparathyroidism cases (approximately 85%) are caused by a single, benign tumor called a parathyroid adenoma. The scan’s main purpose is to pinpoint this small, hyperfunctioning adenoma, which may be difficult to find through physical examination alone. Accurately localizing the abnormal gland pre-operatively enables surgeons to perform a highly targeted, minimally invasive procedure, helping preserve the three remaining healthy glands.
Preparing for the Imaging Procedure
Preparation for the parathyroid scan is generally straightforward, though specific instructions may vary slightly depending on the imaging facility. Patients are typically advised to wear comfortable clothing and remove all jewelry or metallic objects from the neck and chest area, as metal can interfere with the image quality. Some facilities may require the patient to fast for a few hours before the appointment, while others permit eating and drinking as normal.
In certain instances, patients may need to temporarily stop taking specific medications, such as thyroid hormones, especially if a dual-tracer technique is planned, but this decision is always made by the referring physician. The patient should also plan for the total appointment time, which can range from three to five hours, since the procedure involves waiting periods between image acquisitions. Patients who have difficulty lying still for extended periods should discuss this with the medical staff, as remaining motionless is necessary for clear images.
Step-by-Step Guide to the Scan
The parathyroid scan, often called a Sestamibi scan, is a nuclear medicine procedure beginning with the injection of a radioactive tracer into a vein, typically in the arm. The most common tracer is Technetium-99m Sestamibi, which is selectively absorbed by the cells of the parathyroid glands, particularly those that are overactive. This tracer allows the abnormal gland to be visualized because the cells of a hyperfunctioning parathyroid adenoma contain more mitochondria, which actively take up the Sestamibi compound.
The procedure uses a specialized device called a gamma camera to detect the low-level radiation emitted by the tracer. The first, or early, phase involves taking images shortly after the injection, often within the first 10 to 15 minutes. During this initial phase, the tracer is visible in both the thyroid gland and any overactive parathyroid tissue, as well as surrounding blood flow.
The second, or delayed, imaging phase occurs roughly one to three hours later, which is the time required for the tracer to “wash out” of the normal thyroid tissue. The overactive parathyroid adenoma retains the tracer for a longer period, appearing as a persistent “hot spot” on the delayed images. To enhance anatomical detail and three-dimensional localization, the technologist may also perform Single-Photon Emission Computed Tomography (SPECT), which involves the gamma camera rotating around the patient’s neck and chest. Sometimes, a low-dose Computed Tomography (CT) scan is performed simultaneously (SPECT/CT) to fuse the functional image with a detailed anatomical map.
Understanding the Scan Results
A nuclear medicine physician interprets the images by comparing the early and delayed scans to identify areas of persistent radiotracer activity. A “positive” scan is defined by the presence of a bright, localized area of retained activity in the neck or upper chest, which pinpoints the location of the hyperfunctioning parathyroid adenoma. This single, clearly visible hot spot confirms the presence of the abnormal gland and is highly valuable for planning a focused, minimally invasive parathyroidectomy.
A “negative” or inconclusive scan means the tracer did not clearly identify a single, retained hot spot, but this does not necessarily mean the patient does not have hyperparathyroidism. The scan may be negative if the diseased glands are very small, if the patient has multi-gland disease (hyperplasia), or if the adenoma is located in an unusual or ectopic position, such as deep within the chest. The results from the scan are then used by the surgeon to determine the most effective surgical approach, allowing for a targeted operation that reduces recovery time and minimizes scarring compared to traditional surgery.