Localization (i.e. finding the abnormal gland)
In most patients with primary hyperparathyroidism (80%), only one of the four parathyroid glands is diseased these people have what is called a "single adenomaAdenoma - A benign, enlarged, and hyperactive parathyroid gland.." In about 10% of affected people, two or three glands are hyperactive- called "double or triple adenoma." Finally, in 10% of patients, all four glands are hyperacitve- called "four gland hyperplasiaFour gland hyperplasia - When all four glands are hyperactive.." Localizing tests are radiology tests designed to help identify which parathyroid gland(s) are hyperactive. In the past, localization studies were not routinely performed before a first operation because a bilateral neck exploration (an operation where the surgeon examines all four parathyroid glands) was usually performed. (see Bilateral Neck Exploration) However, if a focused parathyroidectomy (an operation where the surgeon examines and removes just the hyperactive gland) is going to be performed then accurate pre-operative localization is an essential component, so most patients undergo some form of pre-operative localization. (see Focused Parathyroidectomy) If a bilateral neck exploration is going to be performed, then pre-operative localization studies may not be necessary. The most commonly performed localizing tests are a sestamibi scanSestamibi scan - Nuclear medicine test where a small amount of radioactive material is injected into a vein and an X-ray is taken. and ultrasound of the neck. Increasingly, high resolution CT (computed tomography or CAT scans) and MRI (magnetic resonance imaging) scans are also showing significant promise. Your surgeon will decide which localizing tests are most appropriate for you.
Sestamibi scans involve injecting a small amount of special radioactive material into a vein and taking an X-ray image of the chest, neck, and head. Sestamibi scans have an accuracy rate of about 80 to 95%. The accuracy of the test is very institution-specific and depends on the quality of the equipment used, the technique used to perform the test, and the skill of the interpreter. Centers that perform a lot of parathyroid surgery typically have more accurate sestamibi scans. The advantages of sestamibi scans are its wide availability and the ability to evaluate for diseased glands outside of the neck at the same time.
Figure 3: Sestamibi scan
Figure 4: Ultrasound
High resolution CAT scan (CT scan) of the neck and chest designed specifically for the parathyroid glands are available at select institutions. While traditional CT scans are not very good at finding diseased parathyroid glands, newer techniques using intravenous (IV) contrast are showing promise in localizing parathyroid glands both in the neck and chest. 42 These specialized CAT scans can have accuracy rates as high as 90 to 95%. 42
Figure 5: CAT scan
Parathyroid Biopsy with parathyroid hormone (PTH) testing may be used if patients are found to have a mass in the neck on ultrasound and it is unclear if it is parathyroid gland or other structure like a thyroid nodule or lymph node. A biopsy can be performed in most centersand is usually done with ultrasound guidance. This involves putting a needle into the mass and removing a few cells from it. These cells can be a) examined under a microscope to see if they resemble parathyroid cells or b) tested for PTH levels.
MRI (magnetic resonance imaging) can also be used to help localize parathyroid abnormalities but the accuracy is not as good as the other tests and is typically only used in cases of re-operative surgery. (see Special Cases: Re-operative Parathyroid Surgery)
Parathyroid venous sampling (selective venous sampling) is another specialized test that may be performed in selected centers. This test is typically only used in cases of re-operative surgery. It can be done in two ways:
- Jugular venous sampling Your surgeon will pass a needle into a large vein (the internal jugular vein) on each side of the neck under ultrasound guidance. A blood sample is taken and tested for PTH levels. Your surgeon is looking to see if one side of the neck has higher levels which would indicate that the overactive gland is on that side. This test does not reveal the exact location of the overactive parathyroid but helps to determine which side it is on.
- Selective venous sampling A radiologist or vascular surgeon inserts a catheter (a plastic tube) into a vein in the groin. It is advanced under guidance into veins in the neck and chest to again sample blood for PTH levels. This test is more invasive and may take longer but allows your surgeon to gain information about blood levels of PTH from both the neck and chest to help pinpoint the location of your abnormal gland.