Since a parathyroid tumor can be in many places in the neck, (and even down in the chest in front of the heart in less than 1% of cases), several types of scans and x-rays have been developed to help determine where the tumor is located. Unfortunately, most parathyroid tumors are only the size of an almond, so they are hard to find and many scans are “negative” because the scan simply can’t see it. As outlined below, there are several types of scans, but none of them are great. All of them are incorrect more than 50% of the time. When scans are “negative” they are wrong nearly 100% of the time (a tumor exists, it just isn’t seen on the scan). Even when these scans are “positive”, they are wrong more than 50% of the time. Because they are so inaccurate (both positive and negative), scans cannot be used to determine if a person has hyperparathyroidism, and they cannot be used to determine who should have a parathyroid operation and who should not. Do not allow the results of your scans to determine who performs your operation and do not allow your doctor to say with confidence that they know where your parathyroid tumor is located because of a scan, since all scans can be wrong even when “positive”. Even if the scan is correct in finding the tumor, 30% of people will have a second tumor that is not seen on the scan (we have a very nice operation video that shows this, illustrating that the best parathyroid surgeons will examine all four parathyroid glands). The bottom line, scans are way over used and way over emphasized. All scans, regardless of who performs them, are wrong more than they are right. Be cautious of a surgeon that puts too much emphasis on the scan.
Sestamibi Scan
The sestamibi scan is the most common scan performed to try to “find” a parathyroid tumor. Virtually all patients will have a sestamibi scan prior to their operation. The quality of this scan is very dependent upon the skill of the people performing it, and the doctor interpreting it. About 40% of sestamibi scans are correctly positive, with about 60% being equivocal or negative. A “negative” scan doesn’t mean you don’t have a parathyroid tumor, it simply means the scan didn’t find it. Most commonly this means the parathyroid tumor is right behind to the thyroid gland and it just can’t be seen. Even when sestamibi scans are “positive”, they are wrong about 50% of the time because thyroid nodules can look like a parathyroid tumor, or the scan is interpreted as lower parathyroid gland and it is actually an upper gland. The take away message is that this scan is not as accurate as doctors think, and because it is often wrong (both positive and negative), the results of this scan should not be used to decide what to do. Like all scans, the sestamibi scan is not a diagnostic or management tool. Be careful of putting too much emphasis on this or any other scan.
The SPECT scan is a different type of Sestamibi scan. It is less accurate at finding parathyroid tumors, but if it does find one, it is better at telling the surgeon where it is located. The makers of this app strongly believe that this scan is over used and over emphasized. In reviewing over 40,000 sestamibi scans we can confidently say that a SPECT scan provides wrong information more often than it provides correct information.
Ultrasound:
The ultrasound scan is the second most used scan for hyperparathyroidism. Again, the quality of this scan is dependent upon the person performing the scan, with the highest quality scans being ones performed by an endocrinologist or surgeon (not a technician). The problem with ultrasound scanning is that the sound waves cannot travel very deep into the tissues, and so about 30% of parathyroid tumors cannot be found simply because they are deeper than the sound waves travel. Another problem with ultrasound scans is that small parathyroid tumors are often confused with lymph glands that occur normally in the neck. Although many doctors rely heavily on ultrasound scans, just like sestamibi scans they are wrong just as often as they are right. Often the ultrasound scan will not show a very large parathyroid tumor because of its location (called a false-negative scan because the patient has a tumor but the scan doesn’t show it). Other times a lymph node or thyroid nodule will be called a parathyroid gland by mistake (called a false-positive scan because this isn’t a parathyroid tumor). Ultrasound scans are way over used, and their results are not nearly reliable as some doctors would like you to believe.
CT Scan and 4-D CT Scan
The CT scan (or CAT Scan) is much less dependent upon the person performing the test than the sestamibi or ultrasound scans. However, this test is less accurate at finding small parathyroid tumors than the ultrasound scan and typically can only find tumors that are medium or large in size. Thus, CT scans, and the more advanced 4-D CT Scan is still wrong at least 50% of the time. Importantly, this test requires IV dye that some people cannot tolerate, and this test is 5 times more expensive than ultrasound and 4 times more expensive than sestamibi. This test is over used and is often wrong.
MRI Scans
MRI scans are very poor at finding parathyroid tumors. There is no role for MRI scans in patients with hyperparathyroidism. This test should never be done to try to find parathyroid tumors. NEVER.
For more information on this topic: http://www.parathyroid.com/sestamibi.htm