How to detect a parathyroid adenoma?

Detection of Parathyroid Adenoma

For optimal detection of parathyroid adenoma, a combination of ultrasound and sestamibi dual-phase scan with SPECT or SPECT/CT is recommended as the initial imaging approach. 1

Initial Diagnostic Approach

First-Line Imaging

• Ultrasound of the neck:

  • Widely recommended as initial localization study with sensitivity of 76-80% and positive predictive value (PPV) of 93% 2
  • Benefits include low cost, no radiation exposure, and ability to evaluate thyroid pathology simultaneously
  • Limitations include operator dependency and difficulty visualizing ectopic glands, particularly in the mediastinum

• Sestamibi dual-phase scan with SPECT or SPECT/CT:

  • Recommended by the American College of Radiology as an equivalent alternative or complementary study to ultrasound 1
  • Provides functional information about hyperfunctioning parathyroid tissue
  • SPECT/CT improves anatomical localization compared to planar imaging alone

Second-Line Imaging

• 4D-CT (CT neck without and with IV contrast):
  • Sensitivity of 62-88% and PPV of 84-90% 2
  • Particularly useful when ultrasound and sestamibi are negative or discordant
  • Leverages unique perfusion characteristics of parathyroid adenomas
  • Typically performed as a 3-phase protocol: noncontrast, arterial, and venous phases 1

Advanced Imaging Techniques

For Difficult Cases or Recurrent/Persistent Disease

• MRI neck:

  • Emerging technique for preoperative localization
  • Useful in patients with contraindications to CT contrast or radiation exposure

• Selective parathyroid venous sampling:

  • Reserved for reoperative surgical candidates with recurrent or persistent hyperparathyroidism
  • Used when noninvasive examinations yield nonlocalizing, equivocal, or discordant results
  • Reported sensitivity ranges from 40% to 93% 1
  • Invasive procedure with potential complications

• [18F]Fluorocholine PET/CT:

  • Newer modality showing promise in localizing parathyroid adenomas
  • May have advantages in detecting upper parathyroid adenomas that are often misidentified by other imaging modalities 3

Optimizing Ultrasound Technique

Systematic Scanning Approach

• Use a combination of techniques:

  • Real-time gray scale imaging
  • Color and power Doppler
  • Graded compression gray scale imaging 4

• For small adenomas (<1 cm), combination techniques are particularly important:

  • Gray scale alone sufficient for only 11% of small adenomas
  • Combined approach required for 89% of small adenomas 4

• Advanced ultrasound technologies:

  • Shear wave elastography (SWE) can help differentiate parathyroid adenomas from thyroid tissue (parathyroid adenomas have lower tissue stiffness) 5
  • 3D ultrasound with color Doppler may improve visualization of the polar artery, a characteristic feature of parathyroid adenomas 5

Common Pitfalls and Challenges

• Misidentification of superior vs. inferior glands:

  • About half of superior parathyroid adenomas are erroneously assigned to the inferior position by both ultrasound and SPECT/CT 3
  • Be particularly vigilant when evaluating suspected inferior adenomas

• Ectopic glands:

  • May be missed on standard imaging
  • Common ectopic locations include the thymus, mediastinum, carotid sheath, and intrathyroidal positions
  • Consider ectopic locations when preoperative localization fails 2

• Multiple adenomas:

  • Present in 15-20% of primary hyperparathyroidism cases 2
  • May require multiple imaging modalities for complete detection
  • Risk factors include MEN syndromes, lithium therapy, and previous radiotherapy 2

• Non-secreting adenomas:

  • Rare but can present as neck masses without biochemical abnormalities
  • Require high clinical suspicion and appropriate imaging 6

Practical Algorithm for Detection

1. Confirm biochemical diagnosis first (elevated calcium and PTH)
2. Start with ultrasound and sestamibi scan with SPECT/CT as complementary first-line imaging
3. If concordant positive results: Proceed to minimally invasive parathyroidectomy
4. If discordant or negative results: Proceed to 4D-CT
5. If still negative: Consider MRI or selective venous sampling in persistent cases

Remember that imaging has no utility in confirming or excluding the diagnosis of hyperparathyroidism but is essential for surgical planning, especially for minimally invasive approaches 2.