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Sestamibi Parathyroid Scanning

Sestamibi is a radioactive pharmaceutical compound delivered intravenously in hospital radiology suites for the purpose of "lighting up" abnormal parathyroid tissue. The compound reveals parathyroid tumors through the use of radiation-detecting technologies such as gamma cameras or radio-guided probes. Sestamibi concentrates rapidly in normal thyroid tissue and parathyroid tissue. After about two hours, this agent "washes out" of normal thyroid and parathyroid tissue, but remains detectable in parathyroid tumors. Thus, a typical outpatient Sestamibi scan consists of two sets of pictures taken by a radiation detector called a gamma camera:

  • An initial picture of normal thyroid and parathyroid tissue taken right after injection of the agent, and
  • A second picture taken two hours later that demonstrates Sestamibi uptake in overactive parathyroid glands

Outpatient Sestamibi Scanning

Outpatient Sestamibi scanning is very helpful when it demonstrates abnormal parathyroid tissue, but in 30 to 40 percent of patients with clear cut hyperparathyroidism, the test fails to demonstrate abnormal glands after two hours. This circumstance occurs commonly if there is abnormal thyroid tissue blocking the parathyroid signal, or if the offending parathyroid tissue is deep within the neck, in multiple locations, or close to a blood vessel.

In most cases, parathyroid tumors are most effectively localized by preoperative high resolution neck ultrasound performed by an endocrinologist. When outpatient Sestamibi scanning and high resolution ultrasound both demonstrate abnormal parathyroid tissue in the same location, the endocrinologist and endocrine surgeon can be very confident that removal of a single gland through a minimally invasive 1-inch incision will be curative.

Intra-operative Sestamibi Scanning

At Memorial Center for Integrative Endocrine Surgery, because our ultrasonography equipment is so effective for preoperative parathyroid localization, Sestamibi is used mainly on the day of parathyroid surgery. The Sestamibi injection is given 90 minutes before surgery. During the actual surgery a narrow radio-guided probe is inserted into the 1-inch incision, and the probe is used to directly find abnormal parathyroid tissue in the neck. This technique detects enlarged parathyroids 90 percent of the time and is not susceptible to many of the shortcomings of the gamma camera.

Unfortunately, even this gamma probe technology misses multiple gland disease in 10 percent of patients. That is why the center's physicians are adamant about the use of rapid intra-operative parathyroid hormone testing. If the rapid PTH determination drops by more than 50 percent after removal of a diseased parathyroid gland, the patient is very likely to be cured of hypercalcemia and hyperparathyroidism.

To learn more about how this method of care has evolved, read the article on Optimization of Minimally Invasive Radio-Guided Parathyroidectomypdf, written by Mack Harrell, MD and David N. Bimston, MD.



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