Ultrasound
Ultrasound scanning is a key part of the assessment and may be performed more than once in the course of investigation and treatment.
Usually it is helpful to have an ultrasound at the time of initial Sestamibi or 4DCT. With a skilled operator, Ultrasound can often identify a parathyroid adenoma and can be used to help interpret the findings of the Sestamibi and 4DCT scan. In addition thyroid nodules are frequently found and these may need to be assessed prior to any neck surgery.
We will repeat the ultrasound in the office during consultation, and this is one of the main reasons for preferring face to face consultation ahead of the time for surgery. Based on our own ultrasound assessment, we can plan the best approach to surgery and if necessary, perform biopsy of thyroid nodules. In some cases it will prove to be appropriate or necessary to have concurrent thyroid surgery.
Once again , when you are asleep and positioned on the operating table, we will perform another ultrasound scan, to confirm previous findings, refresh our plan and position the incision optimally.
Nuclear Medicine Sestamibi scan and or “4D” CT
Both of these tests have their place and may be ordered alone or at times sequentially. They both can assess all of the neck and upper chest.
The resolution of Sestamibi scan depends on the activity of the adenoma rather than its size. Sestamibi is a molecule which is taken up by mitochondria in metabolically active tissue, especially parathyroid adenomas, salivary glands and the heart muscle. When a sestamibi scan is positive it shows that a parathyroid adenoma is metabolically active, not simply enlarged
Not all parathyroid adenomas take up enough Sestambi to be seen. They may also blend in with neighbouring structures such as the thyroid.
The resolution of CT scan is generally only about 1cm and small adenomas may not be seen. A plain, or non-contrast CT can see a lump in the neck, but can not accurately identify what kind of tissue it is.
“4D” CT involves an initial scan followed by intravenous injection of contrast agent and further scans immediately and at subsequent time points, to evaluate the enhancement characteristics of identified nodules. Parathyroid adenomas have variable characteristics but typically are less bright than the thyroid before contrast injection, because they don’t contain iodine. After injection parathyroids typically “enhance” (become more bright), more quickly than thyroid and then “wash out” ( become less bright) more quickly. By their position and characteristics we can often be very confident a lump is or is not a parathyroid.
Other scans:
Fluorocholine PET scan
There are emerging PET techniques including Fluorocholine PET scan which are slightly better than existing technology but not currently funded by medicare or private insurance. We may in some cases discuss such imaging with you.
Parathyroid Venous Sampling (or Selective Venous Sampling)
This technique is uncommonly used when the situation is more complex and routine imaging has been unclear. Most commonly we will use this for patients who have had one or more prior neck surgeries and who will have a scarred neck and predictably difficult re-operation.
We will refer you to an expert radiologist who will place a catheter, via the groin, sequentially into multiple sites within the veins of both sides of the neck and upper chest in order to take bloods samples at every location and to test these for parathyroid hormone level. We can then look for a gradient and interpret the likely side of the neck and general location- high or low. Sometimes the study will suggest the parathyroid is in the chest.
