What is the best imaging modality for visualizing parathyroid glands?

Best Imaging Modalities for Visualizing Parathyroid Glands

The combination of neck ultrasound and sestamibi scan with SPECT/CT provides the most effective approach for visualizing parathyroid glands, with ultrasound serving as the first-line modality due to its high sensitivity (76-80%), cost-effectiveness, and lack of radiation exposure. 1

First-Line Imaging Modalities

Neck Ultrasound

• Sensitivity: 76-80%
• Advantages:
  • Cost-effective and widely available
  • No radiation exposure
  • Can differentiate parathyroid tissue from thyroid nodules
  • Can be performed by surgeons to improve localization 2
• Limitations:
  • Operator-dependent
  • Limited for detecting ectopic glands and multigland disease
  • May miss deep or retro-esophageal glands

Sestamibi Scan with SPECT/CT

• Sensitivity: 88-93%
• Advantages:
  • Provides both functional and anatomical information
  • Superior for detecting ectopic glands
  • Addition of SPECT/CT significantly improves localization over planar imaging alone 3
• Limitations:
  • Radiation exposure
  • Lower sensitivity in multigland disease
  • Variable sensitivity (41-96%) reported in literature 3

Second-Line Imaging Modalities

4D-CT (Four-Dimensional Computed Tomography)

• Sensitivity: 62-88%
• Advantages:
  • Excellent anatomical detail
  • Can detect small adenomas
  • Particularly useful when ultrasound and sestamibi are negative or discordant 1
• Limitations:
  • Higher radiation dose to thyroid gland
  • Controversy regarding optimal number of phases 4

MRI Neck

• Sensitivity: 63-93% (higher with 3.0T)
• Advantages:
  • No radiation exposure
  • Valuable in reoperative cases
  • 3.0T MRI shows promising results with sensitivity up to 98% 3
• Limitations:
  • Less widely available
  • More expensive
  • Most studies are retrospective with small sample sizes 3

Advanced/Specialized Techniques

Selective Parathyroid Venous Sampling

• Sensitivity: 40-93%
• Indications:
  • Reserved for reoperative surgical candidates
  • Recurrent or persistent hyperparathyroidism
  • When non-invasive imaging is inconclusive 1

Emerging Techniques

• PET/CT with 18F-Fluorocholine: Shows promising results with improved imaging and quantification over SPECT 4
• PET/MRI: Potential for simultaneous dynamic contrast-enhanced imaging and co-registered PET imaging with low radiation dose 4
• Shear Wave Elastography: Can help differentiate parathyroid adenomas from thyroid tissue based on tissue stiffness 5
• 3D Ultrasound: May improve visualization of polar arteries and enhance differentiation from lymph nodes 5

Imaging Algorithm

1. Initial Evaluation: Start with neck ultrasound as the first-line modality
2. Complementary Imaging: Add sestamibi scan with SPECT/CT regardless of ultrasound findings
3. Discordant or Negative Results: Proceed to 4D-CT or MRI
4. Persistent Localization Failure: Consider selective venous sampling for reoperative cases

Important Considerations

• Imaging has no role in confirming or excluding the diagnosis of hyperparathyroidism but is used for preoperative localization after biochemical confirmation 1
• The sensitivity of imaging is decreased in multigland disease, concomitant nodular thyroid disease, small adenomas, and mild hypercalcemia 3
• For ectopic parathyroids, which occur in 2-43% of cases, the combination of ultrasound and sestamibi with SPECT/CT significantly increases diagnostic accuracy 6
• Surgeon-performed ultrasound can improve localization rates when sestamibi scans are negative or equivocal, increasing success rates from 80% to 93% 2

Remember that while preoperative localization is crucial for minimally invasive approaches, intraoperative PTH monitoring remains essential to confirm removal of all hyperfunctioning tissue 1.