SCANS TO LOCATE AN ABNORMAL PARATHYROID GLAND
Once the patient is diagnosed with hyperparathyroidism (which is done by laboratory results), we must take every step to identify the location of abnormal gland or glands. As you will have read by now, the patient may have one abnormal gland or a parathyroid adenoma (close to 85% of cases), they may have 2 or more adenomas (multiple parathyroid adenomas,10% of cases), or all 4 glands could be abnormal or parathyroid hyperplasia in 5% of people suffering from hyperparathyroidism.
Ultrasound imaging is a very reliable way to identify an abnormal enlarged parathyroid gland. Ultrasound uses harmless sound waves to look at the structures under the skin, including thyroid, parathyroid, muscles, and blood vessels. Ultrasound should always be the first study to look for an abnormal parathyroid because it is fairly accurate, but does not expose the person to any type of radiation, unlike sestamibi or CT scan. When it is performed by expert radiologists, endocrinologists, or surgeons, it has a high likelihood to show the abnormal partathyroid. In the past decade ultrasound has become available in doctor’s offices, and most parathyroid specialists have an ultrasound machine and can immediately do a scan for the patient when the diagnosis of hyperparathyroidism is confirmed, and begin the process of treating the patients without delay.
Ultrasound can show the exact dimensions of the thyroid gland, enlarged parathyroid glands with the vessels feeding it, carotid artery, lymph nodes, the portion of the thymus that is in the neck, breathing tube (trachea) and the surrounding muscles. The ultrasound image to the left here, shows a very large parathyroid adenoma just below the lower edge of the thyroid gland, roughly an inch and a half deep to the skin. Ultrasound does have it’s limitations; it cannot see behind bone or cartilage, so if a parathyroid adenomas is hiding behind the collar bone, chest bone, breathing tube or voice box.
All expert parathyroid surgeons perform their own ultrasound, to not only confirm the size and location of the abnormal parathyroid but also to asses the relationship of the abnormal gland to adjacent structures (thyroid, carotid artery, recurrent laryngeal nerve), as well as the distance away from the skin. This information is very helpful in planning the surgery and making it be safer. In cases when both an ultrasound and sestamibi scan have been done, and identify an abnormal gland in the same area the accuracy of the findings is greater than 90%. Dr. Larian repeats the ultrasound in the office himself to exactly locate the parathyroid adenoma so that during surgery he knows the exact location, thus further minimizing the surgery.
PROS – 1. Very accurate. 2. Can show the anatomy of the neck very well and create a roadmap for the surgeon to use to access the abnormal parathyroids, and avoid important structures. 3. There is no radiation exposure for the patient. 4. Can be done in the office.
CONS – 1. Hard for the surgeon to visualize the anatomy when the procedure is done at another imaging center and not by the surgeon. 2. Does not show parathyroids that are hiding behind the voice box, breathing tube, chest bone or collar bone. 3. Patients that have thyroid inflammation (Hashimoto’s thyroiditis), will often have lots of enlarged lymph nodes that can be confused on ultrasound for an abnormal parathyroid gland.
A parathyroid sestamibi scan is also an effective way to locate a parathyroid adenoma. In a sestamibi scan, the patient is given a very 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 parathyroid slowly. So an initial scan is compared to the delayed scan to identify the abnormal parathyroid. The sestamibi is a very technical study and can have inaccurate results if 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 locate the abnormal glands in roughly 85% of cases, and when done without expertise it can be much much less accurate. However, there are times when the 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 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 have a low level of activity (too low to be seen on a sestamibi scan).
HOW THE SESTAMIBI WORKS: When the parathyroid gland is producing the PTH hormone (which is a largue protein), 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 it is the more likely it is for sestamibi to attach to it. So in the situation where the PTH levels are very high (above 150 pg/dl) sestamibi scans are most likely to be able to find the abnormal gland. When the PTH is less then 100 the likelihood that this scan will show the abnormal gland is LOW.
As can be seen from the image above the sestamibi scan does not show detailed anatomy, but rather the general area of the abnormal gland, therefore it does not give detailed anatomic information to be used for the surgery.
PROS – 1. Very accurate when the PTH is high (PTH greater than 150 pg/dl). 2. Can show parathyroids that are hiding behind the voice box, breathing tube, chest or collar bones. 3. It can 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 PTH is low (less then 100 pg/dl). 2. Needs to be done by an imaging center with a lot of experience to be done well. 3. Because it uses a radioactive material the patient is exposed to radiation. 4. It does not give detailed anatomic information but rather a general location. 5. The results can be inaccurate if there are thyroid nodules.
SPECT & CT Fusion Scan
SPECT or single-photon emission computed tomography is a more sophisticated 3-dimensional imaging that uses the same radiotracer as the conventional sestamibi parathyroid scan. 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 the enlarged parathyroid gland, and therefore it has greater accuracy. However, just as in the sestamibi scan, this scan must be done by experienced, well-versed imaging centers. Just as in the sestamibi scan it can miss a parathyroid tumor that is not producing a large amount of PTH, and thus this test is also not ideal for people who have a PTH less than 100. The images shown here, clearly 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 the PTH is high. 2. Can show parathyroids that are hiding behind the voice box, breathing tube, chest or collar bones. 3. It can find a gland that is in an ectopic location (unusual spot), as in the upper neck, or down in the chest. 4. More anatomic detail than a sestamibi scan.
CONS – 1. Much less accurate if PTH is low. 2. Needs to be done by an imaging center with a lot of experience to be done well. 3. Because it uses a radioactive material as well as a CT scan the patient is exposed to radiation. 4. Thyroid nodules may affect the results of the scan. 5. Less anatomic information than 4D CT scan or ultrasound.
4D Parathyroid CT Scan
The 4D Parathyroid CT scan is the newest imaging study to locate an abnormal parathyroid. It is the most accurate of the localization studies. It works based on the fact that abnormal parathyroid glands have more blood flowing through them then normal glands, and also the blood passes through the abnormal parathyroid gland at a different rate than the thyroid gland and lymph nodes. This difference is visible when the CT scan is done at different times after the contrast dye is injected into the bloodstream. This type of scan shows the anatomy in great detail which not only identifies the abnormal parathyroid gland but also in relation to the tissue around it, including the thyroid gland, blood vessels, breathing tube, and esophagus. It will show if the abnormal parathyroid is close to the area of the voice box nerve, even though the nerve itself is not visible, the anatomic path is well known to your surgeon. It can also show a gland that is not in the normal position (ectopic parathyroid gland), anywhere from the upper neck and all the way down into the chest.
The 4D parathyroid CT scan is able to identify an enlarged parathyroid better then the other scans mentioned on this page. However, it also exposes the patient to the highest dose of radiation. And although we have modified our 4D CT scan protocol to minimize the dose of radiation it still is a consideration, especially in younger patients. We firmly believe this is the study of choice in patients that have had previous parathyroid surgery and have had recurrence or persistence of disease. And also newly diagnosed hyperparathyroid patients that have a negative ultrasound and PTH levels that are less the 100 pg/dL.
PROS – 1. Very accurate. 2. Can show parathyroid glands anywhere in the neck and chest even if they are hiding behind the voice box, breathing tube, chest or collar bones. 3. More anatomic detail than a sestamibi scan or a SPECT scan. 4. More accurate even when the tumor is small and PTH levels are only slightly elevated.
CONS – 1. Exposure to radiation at a higher dose then Sestamibi or SPECT scans.
Parathyroid Scan FAQs
Dr. Larian understands that patients often have a lot of questions about the imaging tests required for locating parathyroid tumors, and that the choice of which scan to get can be confusing. He has answered some common questions for you below to help you through this process.
Q: Can localization scans help make the diagnosis of hyperparathyroidism?
A: No, the diagnosis of hyperparathyroidism is made by laboratory findings. The scan is only to help identify where the abnormal gland is.
Q: Which scan should be the first choice?
A: Ultrasound should always be the first choice because it only uses sound waves. There is no radiation involved.
Q: Should I be concerned about radiation exposure?
A: Many patients do express some concern in regards to being exposed to radiation for parathyroid scans. First, the decision to proceed with one of the studies that use radiation (Sestamibi, SPECT, or 4D CT scan) should be only after having a negative ultrasound. Having said that, the dose of radiation in these scans is low and not harmful. Knowing the exact location of the abnormal parathyroid allows your surgeon to perform a minimally invasive focused surgery, which minimizes the scarring, trauma to the tissue under the skin, and recovery time.
Q: Where do I go for a Sestamibi SPECT scan?
A: If we are treating a patient who lives in the Los Angeles area for a parathyroid disorder, Dr. Larian will send the patient to one of the local hospitals with great expertise in performing SPECT sestamibi scans. If the patient cannot get to LA for the scan, we will recommend a reputable medical center that performs this type of scan on a regular basis. You have to ask the imaging center how often they perform a sestamibi scan and what is their success rate in identifying the abnormal gland. Less then 70% success rate is not acceptable.
Q: Do all parathyroid surgery patients need a Sestamibi SPECT scan?
A: No, Only ones that have a negative ultrasound study and have a PTH that is higher than 150 pg/dL.
Q: When would you choose a 4D parathyroid CT scan over a SPECT scan?
A: When the patient has had a negative or equivocal ultrasound study and the PTH level is less than 100 pg/dL. The chance of sestamibi or SPECT scan being positive when the PTH is less than 100 pg/dL is significantly lower, because the abnormal gland is not very active and not producing a lot of hormone, this decreases the attraction of the parathyroid to the sestamibi radiotracer, and makes it less likely to attach to it and show up on the scan.
Q: Is a high-resolution CT scan of the neck and upper chest the same as a 4D parathyroid CT scan?
A: No, the 4D parathyroid CT scan is a specialized form of high-resolution CT scan. It not only looks at a thin section of imaging of the neck and the upper chest but also at different time points after injecting the contrast dye. This allows the 4D scan to also see how the contrast that is injected in the blood flows through the tissue which can distinguish between lymph nodes, thyroid tissue and parathyroid. The ability to tell these tissues apart from each is very helpful because on a regular CT scan they can look the same.
Contact The CENTER For Advanced Parathyroid Surgery Today
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.
Dr. Larian is an experienced parathyroid surgeon in Los Angeles with a unique knowledge in the diagnostic testing and their meaning and ramifications the patients suffering from hyperparathyroidism.
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