Primary hyperparathyroidism (PHPT) is a condition in which one or more of the parathyroid glands become overactive, leading to excessive parathyroid hormone (PTH) production and elevated calcium levels in the blood. The definitive treatment for PHPT is surgical removal of the abnormal gland(s), known as parathyroidectomy. Before surgery, accurate localization of the overactive gland(s) is helpful for surgeons as it provides a “roadmap” of where we should look for the abnormal gland
Why Radiological Studies Are Important
Radiological imaging helps in:
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- Localizing the abnormal parathyroid gland(s) to guide the surgeon.
- Distinguishing between single-gland and multi-gland disease, which affects surgical planning.
- Reducing surgical time and invasiveness, enabling a more targeted and minimally invasive approach.
- Identifying ectopic parathyroid glands, which may be located outside the usual anatomical position.
Key Radiological Studies Used in PHPT Management
Ultrasound
How it Works: High-frequency sound waves create an image of the thyroid and parathyroid glands.
Advantages: Non-invasive, widely available, and does not involve radiation. Also identifies the presence of thyroid nodules that may require intervention at the time of parathyroidectomy.
Limitations: Operator-dependent; may not detect small or deep-seated parathyroid adenomas.
Sestamibi Scintigraphy (Technetium-99m Sestamibi Scan)
How it Works: A radioactive tracer (sestamibi) is injected into the bloodstream. Overactive parathyroid tissue absorbs the tracer and appears as a “hot spot” on imaging.
Advantages: Effective in detecting single adenomas and can help guide surgery.
Limitations: Less accurate in cases of multi-gland disease or small adenomas.
4D CT Scan (Four-Dimensional Computed Tomography)
How it Works: A high-resolution CT scan captures images at multiple time points after contrast injection, highlighting blood flow and enhancement patterns.
Advantages: Highly sensitive and useful for detecting ectopic parathyroid glands in the chest or deep neck.
Limitations: Higher radiation exposure than ultrasound or sestamibi. 4DCT is still a relatively new imaging study for PHPT in Melbourne and the skill required to produce a high quality result is dependent on where this scan is performed.
Occasionally, an abnormal gland may not be identified in radiological studies. This may be due to:
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- Multiglandular disease leading to smaller glands that are harder to identify
- Scans not being performed optimally (eg. Inappropriate timing of injection of the contrast agent and scanning at the correct time) and missing the abnormal parathyroid gland(s) as a consequence
- Lack of experience in interpreting results and not being reported correctly
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It is important to note that the diagnosis of PHPT is based on blood tests, not on radiological studies. The absence of an abnormal parathyroid gland in radiological studies should not prevent surgical intervention.
Conclusion
Radiological studies are an essential component of PHPT management, helping surgeons localize the overactive gland, increase surgical success, and minimize invasiveness. A combination of ultrasound, sestamibi scans and 4D CT is commonly used.
