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Endocrine · Parathyroid

Parathyroid Imaging

Snapshot

Imaging in primary hyperparathyroidism is for pre-operative localisation only — it never makes the diagnosis (that is biochemical). Workhorses: ⁹⁹ᵐTc-sestamibi with SPECT/CT and, increasingly, ¹⁸F-fluorocholine PET/CT (most sensitive, ≈92%). Ultrasound is complementary; concordant ultrasound + sestamibi → focused parathyroidectomy.

Read the full article →In-depth, fully referenced version
≈92%¹⁸F-fluorocholine Se
≈80–90%Sestamibi SPECT/CT (single)
SPECT/CTLocalisation & ectopics
Multigland ↓Sensitivity falls
Reference values
  • Sestamibi: 400–900 MBq (EANM 2021); some US protocols use up to ~1,110 MBq.
  • Dual-phase: early 10–15 min, delayed 90–150 min (EANM 2021).
  • Subtraction: ¹²³I 7.4–14.8 MBq, sestamibi 2 h later with simultaneous dual-window imaging; or ⁹⁹ᵐTc-pertechnetate 74–150 MBq (EANM 2021).
  • SPECT/CT: 128×128, 360°, 60–120 projections ×15–25 s; low-dose CT ~120 kVp.
  • ¹⁸F-fluorocholine: ~100 MBq, image 5 & 60 min; effective dose ≈2 mSv.
  • Sensitivity: US 76%, sestamibi-SPECT 79%, 4D-CT 89%, fluorocholine PET ≈92% (95% single-gland).
  • Multigland: sestamibi SPECT/CT ≈34%, dual-phase ≈22%.
  • Detection ≳500 mg; ~10–15% rapid washout; ectopic in ~6–16%.

Tracers & mechanism

  • Sestamibi — lipophilic cation, retained in mitochondria-rich oxyphil cells; washes out slower than thyroid (basis of dual-phase). P-glycoprotein efflux → fast washout → false negatives.
  • ¹⁸F-fluorocholine — choline analogue; ↑ membrane synthesis in hyperfunctioning cells; higher target-to-background than sestamibi.
  • ¹²³I / ⁹⁹ᵐTc-pertechnetate — taken up by thyroid only (NIS); used to subtract thyroid.

Sestamibi — dual-phase

  • Early (10–15 min) + delayed (90–150 min): adenoma persists on delayed while thyroid washes out.
  • Fails with fast-washout adenomas (~10–15%) or sestamibi-avid thyroid nodules.

Dual-tracer subtraction

  • Sestamibi image − thyroid image (¹²³I or pertechnetate) = parathyroid-only focus.
  • Better than dual-phase for fast washout and thyroid nodules; needs good registration.

SPECT / SPECT-CT

  • 3-D localisation; SPECT/CT separates parathyroid from thyroid and finds ectopics — recommended standard.
  • Adds localisation accuracy/specificity more than raw sensitivity.

¹⁸F-fluorocholine PET/CT

  • Most sensitive: ≈92% (95% single-gland, 88% multigland), specificity ≈99%.
  • Best for negative/discordant imaging, multigland, small or ectopic glands, re-operative cases; lower dose than sestamibi.

Modality comparison

ModalitySensitivityNotes
Ultrasound≈76%
Operator-dependent; poor for mediastinum
Sestamibi dual-phase≈48–70%
Fails with fast washout / thyroid nodules
Sestamibi SPECT/CT≈80–90% (34% multigland)Standard; best anatomical map
¹⁸F-fluorocholine PET/CT≈92% (95% single-gland)Most sensitive; lower dose
4D-CT≈89%
Good anatomy; higher radiation

How to read it

  • Dual-phase → focus persisting on delayed images.
  • Subtraction → what remains after the thyroid image is removed.
  • SPECT/CT & PET/CT → assign to a quadrant vs an ectopic site; report side and level.
  • Ectopic: superior → tracheo-oesophageal groove / retro-oesophageal / posterior mediastinum; inferior → thymus / anterior mediastinum, intrathyroidal, undescended.
  • Always state ultrasound concordance and single- vs multigland pattern.

Choosing the test

  • First-line: ultrasound + functional (sestamibi SPECT/CT or fluorocholine PET); concordant → focused surgery.
  • Negative / discordant → fluorocholine PET/CT (or 4D-CT).
  • Multigland / familial → fluorocholine PET; avoid focused surgery.
  • Re-operative → fluorocholine PET + SPECT/CT + ultrasound; consider venous sampling.
  • Secondary/tertiary (renal) HPT → imaging less reliable; used selectively.

Special situations

  • Multigland disease — main false-negative cause (conventional ≈22–34%); fluorocholine best.
  • Ectopic / supernumerary glands — commonest reason for failed exploration.
  • Concurrent thyroid disease — degrades sestamibi specificity; use subtraction / SPECT-CT / PET.

Pitfalls & false results

  • False + : thyroid nodules (oncocytic/Hürthle, follicular adenomas).
  • False − : small glands (<500 mg), multigland disease, fast washout.
  • Imaging does not diagnose HPT (biochemical) — a negative scan only means failed localisation.
  • One avid focus ≠ single-gland disease — confirm with intra-operative PTH.

Sources

  1. SNMMI / EANM parathyroid scintigraphy guideline — protocol, doses, SPECT/CT.
  2. EANM guidance on ¹⁸F-fluorocholine PET/CT in primary hyperparathyroidism.
  3. Cheung K et al. Meta-analysis of pre-operative localisation (Ann Surg Oncol) — pooled sensitivities.
  4. ¹⁸F-fluorocholine vs sestamibi/tetrofosmin SPECT/CT (J Nucl Med).
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