Sestamibi Scans: details about technique and what to expect

If hyperparathyroidism is confirmed through blood tests showing elevated parathyroid and calcium levels, additional tests will be needed before parathyroid disease treatment.

Treatment of parathyroid disease involves removal of the affected parathyroid gland or glands in order to lower parathyroid hormone levels and eliminate symptoms of high calcium. Determining how many glands are affected is important for surgical planning. If only one gland is affected, radioguided surgery for hyperparathyroidism can be performed, a minimally invasive parathyroid surgery. A sestamibi scan is frequently ordered to evaluate all four parathyroid glands, in efforts to determine which is diseased.

A sestamibi scan is a nuclear scan. Sestamibi is a compound that is bound to the radioactive isotope Tc99m. It is therefore often referred to as Tc99m-sestamibi. This pharmeceutical binds to active parathyroid tissue. When calcium levels are high (as they are in all patients with primary hyperparathyroidism), normal parathyorid glands will be inactive, meaning they are not actively making parathyroid hormone. These tissues will not take up Tc99m-sestamibi. Therefore, the priniple of this test is that only abnromal, overactive parathyroid glands will appear on this scan.

This test will take approximately 2 hours, depending on the location of the test. This test begins with injection of Tc99m-sestamibi into a vein. This compound is radioactive, but is only mildly radioactive and therefore safe. Imediately folowing this injection, initial images of the neck and chest are taken as a baseline image. After approximately 2 hours, another set of images of the head and neck are taken. Ideally, these images should show a "hot spot," usually a small round, darkened area in the neck, to indicate the abnormal parathyroid glands. If this is the case, the parathyroid surgeon can identify the location of the abnormal gland in the neck and minimally invasive parathyroid surgery will be possible. If multiple "hot spots" appear, more than one gland is likely affected. Minimally invasive parathyroid surgery may or may not be possible; this will have to be discussed between the patient and doctor. If no "hot spots" appear, it is called a negative scan. A negative scan does not mean there is no parathyroid disease. Approximately 15% of patient with primary hyperparathyroidism have negative scans. In cases of a negative scan, the surgeon explores all the four parathyroid glands during surgery and identifies the abnormal gland with direct visualization.