Sestamibi Scan
A parathyroid sestamibi scan is an effective way to locate a parathyroid adenoma. In a sestamibi scan, a patient is given a small amount of radioactive dye (sestamibi radiotracer) that becomes quickly absorbed by an abnormal functioning parathyroid gland, as well as the thyroid. In the following few hours, the material leaves the thyroid quickly and the abnormal parathyroid slowly. Next, an initial scan (ideally done within 5-10 minutes of the injection) is compared to a delayed scan (2 hours later) to identify an abnormal parathyroid. The sestamibi is a technical study and can have inaccurate results if it is done at a facility that does not have a lot of experience doing this scan.
Even when the study is done by expert radiologists, sestamibi scans are only able to help locate abnormal parathyroid glands in roughly 85% of cases. When done without expertise, a sestamibi scan can be much less accurate. However, there are times when a parathyroid is either too small or not able to concentrate the sestamibi and won’t show activity on the scan; this does not mean that there is not an abnormal gland, but rather that the gland is not active enough to show on this type of study. It’s also possible that there are multiple minimally active parathyroid adenomas, or that all four glands are abnormal, and each has a low level of activity (too low to be seen on a sestamibi scan).
How a Sestamibi Scan Works: When the parathyroid gland produces parathyroid hormone (PTH), it uses a fair amount of energy. The part of the cell that creates the energy is called mitochondria, and the sestamibi nuclear material is attracted to the actively working mitochondria. The more active the mitochondria is, the more likely it is for sestamibi to attach to it. So, in the situation where PTH levels are high (above 150 pg/dl), sestamibi scans are most likely to be able to help find an abnormal gland. When a patient’s PTH level is less than 100, the likelihood that this scan will show an abnormal gland is low.
The other limitation of sestamibi nuclear material is that not all parathyroid cells have the same number of mitochondria. In the parathyroid glands the oxyphil parathyroid cells have a lot more mitochondria then the chief cells. Therefore, the different types of parathyroid tumor that have different proportions of oxhphil and chief cells will respond differently to the sestamibi injection based, making it a less consistent scan.
As can be seen from the image above, the sestamibi scan does not show detailed anatomy of the person’s neck, but rather the general area of an abnormal gland. Therefore, the parathyroid scan does not give detailed anatomic information that can be used for surgery. Additionally, you can see activity in multiple salivary glands, some thyroid nodules, as well as other tissues that can be misleading.
PROS – 1. Very accurate when a patient’s PTH level is high (PTH greater than 150 pg/ dl). 2. Can show parathyroids that are hidden behind the voice box, breathing tube, chest bone, or collarbone. 3. It can be used to find a gland that is in an ectopic location (unusual spot), as in the upper neck, or down in the chest.
CONS – 1. Much less accurate if a patient’s PTH level is low (less than 100 pg/dl). 2. Needs to be done at an imaging center with a lot of experience to ensure accurate results. 3. Because it uses radioactive material, a patient is exposed to radiation. 4. It does not give detailed anatomical information, but rather a general location. 5. The results can be inaccurate if there are thyroid nodules.
SPECT & CT Fusion Scan
SPECT (single-photon emission computed tomography) is a sophisticated 3D imaging parathyroid scan that uses the same radiotracer as a conventional sestamibi scan, and it fuses the images of a sestamibi scan with a CT scan done at the same time. This combination of images can help pinpoint the exact location of an enlarged parathyroid gland, and therefore, it has greater accuracy than a sestamibi scan performed on its own. However, just as in the sestamibi scan, SPECT imaging must be done at experienced, well-versed imaging centers. Just as in the sestamibi scan, a SPECT scan can miss a parathyroid tumor that is not producing a large amount of PTH. Thus, a SPECT test is not ideal for people who have a PTH level of less than 100. The images shown here point at a parathyroid adenoma (orange dot) in the right inferior aspect of the lower neck, just above the chest bone.
PROS – 1. Very accurate when a patient’s PTH level is high. 2. Can show parathyroids that are hidden behind the voice box, breathing tube, chest bone, or collarbone. 3. It can be used to find a gland that is in an ectopic location (unusual spot), as in the upper neck or down in the chest. 4. More anatomical detail than a sestamibi scan.
CONS – 1. Much less accurate if a patient’s PTH level is low. 2. Needs to be done at an imaging center with a lot of experience for accurate results. 3. Because it involves the use of radioactive material as well as a CT scan, a patient is exposed to radiation. 4. Thyroid nodules may affect the results of the scan. 5. Less anatomical information than a 4D parathyroid CT scan or parathyroid ultrasound.
Parathyroid Scan FAQ
At the CENTER, Dr. Larian is able to find a great majority of abnormal parathyroids on ultrasound alone. A parathyroid surgeon performing an ultrasound has the added advantage of being to able to compare ultrasound findings to what they see in surgery; this in time gives the parathyroid surgeon an exceptional amount of insight.
A minority of patients require multiple localization studies to identify an abnormal parathyroid gland. Each localization study is used to help create a personalized treatment plan for a patient, and ultimately, ensure that a patient can alleviate HPT symptoms.
Contact The CENTER For Advanced Parathyroid Surgery Today
Dr. Larian is an experienced parathyroid surgeon in Los Angeles with over 2 decades of experience in hyperparathyroidism surgery. unique knowledge in parathyroid gland diagnostic testing and the meaning and ramifications of parathyroid gland testing for patients suffering from HPT. Dr. Larian is happy to perform localization studies to help a patient diagnose HPT. And if a patient is dealing with HPT, Dr. Larian can provide a custom treatment recommendation.
If you feel as though you may be experiencing parathyroid problems and would like to speak with an expert parathyroid surgeon today, we encourage you to contact our CENTER by calling 310.461.0300 to set up an initial consultation.