Imaging tests are a crucial component of the preoperative planning process for patients diagnosed with primary hyperparathyroidism. Once blood tests have confirmed that a parathyroid gland is overactive, the next clinical challenge is to determine exactly which of the four glands is the source of the problem. Because parathyroid glands are very small and their exact location in the neck can vary between individuals, specialised scans are used to provide a “roadmap” for the surgeon. These tests do not diagnose the condition as that is done via biochemistry but they are essential for facilitating minimally invasive surgical techniques. By precisely localising a benign adenoma, clinicians can reduce operative time, minimise scarring, and improve the overall success rate of the treatment.
What We’ll Discuss in This Article
- The primary role of neck ultrasound in identifying glandular enlargement.
- The function and procedure of a Sestamibi (nuclear medicine) scan.
- How SPECT/CT technology provides three-dimensional localisation.
- The use of 4D-CT scans for complex or recurrent cases.
- Why imaging is used for surgical planning rather than diagnosis.
- What happens when imaging tests fail to find an abnormal gland.
Ultrasound Scans for Parathyroid Localisation
A neck ultrasound is frequently the first imaging test performed because it is non invasive, does not involve radiation, and is highly effective at identifying enlarged glands. During the procedure, a radiologist or sonographer uses high frequency sound waves to create images of the structures in the neck, including the thyroid gland and the surrounding tissues. While normal parathyroid glands are usually too small to be seen on an ultrasound, an overactive gland that has developed into an adenoma is typically larger and has a distinct appearance.
The success of an ultrasound depends heavily on the skill of the operator and the location of the gland. If the abnormal gland is tucked behind the windpipe or has descended into the chest, it may not be visible. However, when an ultrasound successfully identifies a single enlarged gland that matches the biochemical data, it provides the surgeon with a clear target.
Sestamibi and SPECT/CT Scans
The Sestamibi scan is a specialised type of nuclear medicine imaging that is considered a gold standard for parathyroid localisation. During this test, a small amount of a mildly radioactive tracer called Technetium-99m Sestamibi is injected into a vein. This tracer is absorbed by both the thyroid and parathyroid glands, but it “washes out” of normal thyroid tissue much faster than it does from an overactive parathyroid gland. Images are taken shortly after the injection and again several hours later to see where the tracer remains.
To improve accuracy, many UK hospitals now use SPECT/CT, which combines the functional data of the Sestamibi scan with the anatomical detail of a CT scan. This creates a three-dimensional image that shows exactly where the overactive gland is located in relation to the spine, blood vessels, and windpipe. This is particularly helpful for “ectopic” glands, which are parathyroid glands located in unusual places, such as the upper chest or deep in the neck muscles. The Sestamibi scan is highly sensitive, although its effectiveness can be reduced if the patient also has thyroid nodules that absorb the tracer.
The Role of 4D-CT Imaging
Four-dimensional computed tomography, or 4D-CT, is an advanced imaging technique used when standard scans fail to locate the abnormal gland. The “fourth dimension” in this test refers to the way the contrast dye moves through the parathyroid tissue over time. Overactive parathyroid glands have a unique blood flow pattern; they tend to take up the contrast dye very quickly and then “wash it out” faster than the surrounding lymph nodes or thyroid tissue.
Because 4D-CT provides very high resolution images, it is exceptionally useful for finding very small adenomas or for planning “re-do” surgeries where a previous operation was unsuccessful. It provides the most detailed anatomical roadmap available, though it does involve a higher dose of radiation compared to ultrasound or Sestamibi. The Royal College of Radiologists highlights that 4D-CT is an increasingly valuable tool for complex parathyroid localisation, particularly in cases of multi-gland disease or surgical failure.
Why Imaging is Not for Diagnosis
It is a vital clinical distinction that imaging tests are used for localisation, not for the initial diagnosis of hyperparathyroidism. A scan might show a small lump in the neck that looks like a parathyroid adenoma, but if the blood calcium and parathyroid hormone levels are normal, that lump is not causing a disease. Conversely, if the blood tests confirm hyperparathyroidism but the scans are all negative, the patient still has the condition; the gland is simply too small or too well hidden to be seen.
Surgeons use these tests primarily to decide if they can perform a “focused” parathyroidectomy (a small incision on one side of the neck) or if they need to perform a “four gland exploration” (checking all glands through a central incision). If two different types of scans (such as ultrasound and Sestamibi) both point to the same spot, the surgeon can be very confident in a focused approach. If the scans disagree or are negative, the surgeon will typically examine all four glands during the operation to ensure the source of the high calcium is removed.
| Imaging Test | Primary Advantage | Main Limitation |
| Ultrasound | No radiation; identifies glands near thyroid. | Operator dependent; cannot see behind bone/air. |
| Sestamibi | Shows gland function; finds ectopic glands. | Less effective if thyroid nodules are present. |
| SPECT/CT | 3D anatomical and functional mapping. | Requires injection of radioactive tracer. |
| 4D-CT | Highest resolution; identifies tiny adenomas. | Higher radiation dose; requires IV contrast. |
What Happens if Scans are Negative?
It is not uncommon for a patient with confirmed hyperparathyroidism to have “negative” or inconclusive imaging. This occurs in approximately 15 to 20 percent of cases. A negative scan does not mean that the disease is absent; it simply means that the overactive gland is not large enough or active enough to be detected by current technology. In these situations, UK surgeons are still able to perform a highly successful operation by carefully examining all four parathyroid glands during surgery.
In some complex or recurrent cases where standard imaging has failed, specialised centres may use even more advanced tests, such as a PET-CT scan using a specific tracer called Choline. NHS England provides specialised commissioning for these advanced imaging techniques in tertiary centres to ensure that patients with difficult to locate glands receive the best possible preoperative planning. Regardless of the imaging results, the goal remains the same: to identify and remove the overactive tissue and restore normal calcium balance.
Conclusion
Imaging tests such as ultrasound, Sestamibi scans, and 4D-CT provide essential information for locating abnormal parathyroid glands before surgery. While these tests are not used to diagnose the condition—which is done through blood work—they allow for safer and more focused surgical procedures. Combining different types of scans increases the likelihood of finding the overactive gland, even when it is in an unusual location. If you experience severe, sudden, or worsening symptoms, call 999 immediately.
Do I need to do anything to prepare for a Sestamibi scan?
Usually, no special preparation is needed, though you should inform the staff if you are pregnant or breastfeeding. You may be asked to remove jewellery or metal objects that could interfere with the images.
Is the radiation from these scans dangerous?
The amount of radiation used in a Sestamibi or SPECT/CT scan is very low and considered safe for most adults. The benefit of accurately locating the gland for surgery far outweighs the minimal risk.
Why did my ultrasound find nothing even though my calcium is high?
Ultrasound is limited by what it can see through. If the gland is deep in the neck, behind the windpipe, or in the chest, the sound waves cannot reach it.
Can these scans find parathyroid cancer?
While these scans find enlarged glands, they cannot definitely tell if a gland is cancerous. However, parathyroid cancer is extremely rare (less than 1 percent), and most enlarged glands are benign.
How long do these imaging tests take?
An ultrasound usually takes 20 to 30 minutes. A Sestamibi scan is a longer process, often involving an initial scan and then a repeat scan 2 to 4 hours later.
Will the scans show my thyroid as well?
Yes, most neck scans will show the thyroid gland. Sometimes, thyroid nodules can be seen, and the radiologist will note these as they can occasionally be confused with parathyroid glands.
What if I am allergic to the dye used in CT scans?
If you have a known allergy to iodine or contrast media, you must tell the medical team. They may use an alternative test like ultrasound and Sestamibi, which do not use iodine-based contrast.
Authority Snapshot (E-E-A-T)
The Medical Content Team at MyPatientAdvice delivers evidence based health education for the UK public, prioritizing clinical safety and accuracy. This article has been reviewed by Dr. Stefan Petrov, a UK trained physician with experience in internal medicine, surgery, and diagnostic imaging. All information regarding parathyroid localisation and surgical planning is strictly aligned with the standards of the NHS and the National Institute for Health and Care Excellence (NICE).
