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Parathyroid scintigraphy
Parathyroid scintigraphy does not diagnose hyperparathyroidism — the diagnosis is biochemical — but localises the adenoma before minimally invasive surgery, based on slow washout of sestamibi from a mitochondria-rich adenoma compared with fast washout from the thyroid.
Why it matters in the exam
The exam presents a patient with high calcium and PTH who is sent for scintigraphy, and asks about the principle, the protocol or the reason for a negative result. The principle: Tc-99m sestamibi is taken up by both thyroid and parathyroid, but washes out of the thyroid within about an hour and stays in the adenoma, which is rich in oxyphil cells and mitochondria; on the delayed image (about two hours) a hot focus remains. In the subtraction method, pertechnetate or I-123, which are taken up only by the thyroid, is added and the images are subtracted.
SPECT/CT improves three-dimensional localisation, finds ectopic adenomas (mediastinal, intrathyroidal, retro-oesophageal) and guides the surgeon. Causes of a false-negative result: a small adenoma, hyperplasia of several glands (multigland disease), an adenoma with few oxyphil cells and fast washout, and drugs such as calcium channel blockers. Causes of a false positive: a thyroid nodule, an inflamed lymph node and thyroid cancer. The scan is therefore combined with neck ultrasound, and two concordant studies allow a focused operation on one side only.
F-18 fluorocholine PET/CT is more sensitive than sestamibi, especially for small adenomas, multigland disease and after a failed previous operation, and it is accepted as a second-line study and in many centres as the first. 4D-CT is a radiological alternative. In hyperparathyroidism secondary to renal failure, imaging is not needed for diagnosis and is used only sometimes before re-operation. The decision to operate rests on clinical and biochemical criteria, not on the scan; a negative scan does not cancel surgery but leads to bilateral neck exploration.
Key points
- The diagnosis is biochemical; the scan localises before surgery.
- Sestamibi washes out of the thyroid and stays in the adenoma.
- SPECT/CT finds ectopic adenomas.
- F-18 fluorocholine PET/CT is more sensitive, especially after failed surgery.
- A negative scan does not cancel surgery.
Summary table
| Method | Principle | Advantage | Limitation |
|---|---|---|---|
| Dual-phase sestamibi | Slow washout from the adenoma | Available and simple | Low sensitivity in multigland disease |
| Sestamibi–pertechnetate subtraction | Removes the thyroid from the image | Helps with thyroid nodules | Sensitive to motion |
| SPECT/CT | Three-dimensional localisation | Ectopic adenomas | Slightly higher radiation dose |
| F-18 fluorocholine PET/CT | Uptake in proliferating cells | High sensitivity, re-operation | Availability and cost |
| 4D-CT | Enhancement pattern over time | Precise localisation | Radiation to the thyroid |
A free exam question
איזה שילוב ממצאים ניתן למצוא בבדיקות מעבדה בהיפרפאראתירואידיזם ראשוני? )יש לסמן את התשובה המדויקת ביותר( (the question as examined, in Hebrew)
- א. עלייה ב- PTH ובקלציום, ירידה בפוספאט בדם, וקלציום-פוספאט גבוהים בשתן
- ב. עלייה ב- PTH ,בקלציום ובפוספאט בדם, וקלציום-פוספאט גבוהים בשתן
- ג. עלייה ב- PTH , ירידה בקלציום ובפוספאט בדם, וקלציום-פוספאט נמוכים בשתן
- ד. עלייה ב- PTH ,ירידה בקלציום, פוספאט גבוה בדם, וקלציום-פוספאטנמוכים בשתן
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Sources
- EANM Practice Guidelines for Parathyroid Imaging, 2021 — Tc-99m sestamibi techniques and F-18 fluorocholine PET
- AAES Guidelines for Definitive Management of Primary Hyperparathyroidism, 2016 — Preoperative localisation
- SNMMI Procedure Standard for Parathyroid Imaging, 2021 — Dual-phase and subtraction protocols
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.