Sestamibi Parathyroid Scanning (Out-patient Technique and Intra-operative Technique)
Sestamibi is a radioactive compound that is given by vein in hospital radiology suites for the purpose of “lighting up” abnormal parathyroid tissue, so that parathyroid tumors can be seen by radiation-detecting technology (gamma camera or radioguided probes). Sestamibi is rapidly concentrated in normal thyroid tissue and parathyroid tissue. After about 2 hours, this agent “washes out” of normal thyroid and parathyroid tissue, but remains detectable in parathyroid tumors. Thus, a typical out-patient 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 2 hours later that demonstrates Sestamibi uptake in overactive parathyroid glands
Out-patient Sestamibi scanning is very helpful when it demonstrates abnormal parathyroid tissue, but in 30-40% of patients with clear cut hyperparathyroidism, the test fails to demonstrate abnormal glands at 2 hours. This circumstance occurs commonly if there is abnormal thyroid tissue blocking the parathyroid signal or when the offending parathyroid tissue is deep in the neck, in multiple locations or close to a blood vessel.
In these cases, pre-operative high resolution neck ultrasound performed by an endocrinologist is the localization procedure of choice for parathyroid tumors. When out-patient 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 1” minimally-invasive incision will be curative.
At Ft. Lauderdale Endocrine Surgery, we use Sestamibi a second time on the day of surgery. The injection is given 1.5 hours before surgery starts. During the actual surgery we insert a narrow radioactive probe into our 1” minimally invasive incision and use the probe to find abnormal parathyroid tissue in the neck directly. This technique detects enlarged parathyroids 90% of the time and is not susceptible to many of the pitfalls of the gamma camera. Unfortunately, even the gamma probe technology misses multiple gland disease in 10% of patients. That is why we are adamant about the use of rapid intra-operative parathyroid hormone testing as our final gold-standard for cure. If the rapid PTH determination drops by more than 50% after we have removed a diseased parathyroid gland, the patient is very likely to be cured of his/her hypercalcemia and hyperparathyroidism.
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