What is a parathyroid scan?
Four parathyroid glands sit behind the thyroid gland in the neck. They are small and not easily located.
These glands regulate calcium levels in the body. Sometimes they become overactive and the calcium levels become high enough to start causing various problems. In this case they need to be excised (cut out).
The diagnosis of hyperparathyroidism is made using the clinical signs and symptoms and demonstrating high parathyroid hormone levels and calcium levels. Once this has been confirmed you can be sent for the scan to help locate the offending gland. There are usually 4—you want to have the right one removed.
A non-specific chemical that gets taken up in living tumour cells (benign or malignant) called Sestamibi is labelled to a radioactive substance that emits gamma rays that can be detected using a special machine called a gamma camera. Since a parathyroid adenoma is a tumour (non-cancerous) is usually concentrating this substance and a focal area can be demonstrated on imaging that increases in intensity over time.
Sometimes, however, the thyroid also takes up this tracer and it becomes hard to identify the focal adenoma. In this case a second tracer with similar radioactive properties, but that only gets concentrated in the thyroid gland, is also injected.
The two data sets are subtracted from each other to give you images that only show the parathyroid adenoma according to the following equation:
Sestamibi (thyroid + parathyroid) data – Thyroid scan (thyroid) data = Remaining parathyroid data only
What can I expect to happen?
The Sestamibi is injected followed by static imaging at 15 minutes, at 1 hour, 2 hours and 3 hours to demonstrate the increased tracer concentration with time.
At three hours the pertechnetate is injected and imaged 20 minutes later.
The nuclear physician will process and report the study.
