What should be ordered on an ultrasound test for the diagnosis of primary hyperparathyroidism (PHPT)?

Ultrasound Assessment for Primary Hyperparathyroidism

For diagnosis of primary hyperparathyroidism (PHPT), ultrasound should focus on identifying enlarged parathyroid glands in typical locations posterior to the upper and lower poles of the thyroid gland, but should only be performed after biochemical confirmation of the disease. 1

Diagnostic Principles

• The diagnosis of PHPT is biochemical, not radiological, requiring elevated or high-normal serum calcium with concurrent elevated or inappropriately normal PTH levels 2
• Imaging studies, including ultrasound, have no role in confirming or excluding the diagnosis of PHPT but are used solely for preoperative localization 3, 1
• Ultrasound is performed to localize abnormally functioning parathyroid glands to facilitate targeted curative surgery, particularly minimally invasive parathyroidectomy (MIP) 3

Key Ultrasound Features to Assess

• Typical locations of parathyroid adenomas: posterior to the upper and lower poles of the thyroid gland 1
• Characteristic sonographic features of parathyroid adenomas:
  • Hypoechoic, homogeneous nodules 4
  • Lower tissue stiffness compared to thyroid tissue (if shear wave elastography is available) 4
  • Presence of a polar feeding artery (visible with color Doppler) 5
• Adenomas located at the caudal margin of the thyroid are more easily detected (92% sensitivity) compared to those at the cranial margin (23% sensitivity) 5

Ultrasound Performance Characteristics

• Sensitivity for detecting single parathyroid adenomas ranges from 57-73% 6, 7
• Specificity is high, ranging from 94-100% 6, 8
• Detection of feeding vessels by color Doppler significantly improves diagnostic accuracy (93% vs 39% when vessels are not visualized) 5
• Ultrasound is less sensitive for detecting multiglandular disease, with sensitivity dropping to 70% or lower 6

Complementary Imaging Modalities

• When ultrasound is negative or inconclusive, additional imaging is recommended:
  • Sestamibi dual-phase scan with SPECT or SPECT/CT 3
  • CT neck without and with IV contrast (4D-CT) 3
• Combining ultrasound with nuclear imaging techniques improves overall sensitivity to 78-98% 6, 7

Special Considerations

• Ultrasound is particularly useful for reoperation cases with sensitivity of 80% and specificity of 92% 8
• For secondary and tertiary hyperparathyroidism (typically multiglandular disease), ultrasound sensitivity for detecting ectopic glands is much lower (7-32%) 3, 1
• Ultrasound is less effective for detecting ectopic parathyroid glands, particularly those in the mediastinum 3

Common Pitfalls to Avoid

• Relying on imaging to make the diagnosis of PHPT (diagnosis is biochemical) 2
• Failing to use color Doppler to identify feeding vessels, which significantly improves diagnostic accuracy 5
• Not examining the entire neck region, including potential ectopic locations 3
• Mistaking lymph nodes or thyroid nodules for parathyroid adenomas 4

Ultrasound remains a first-line imaging modality for PHPT due to its convenience, availability, and low cost, but should always be performed after biochemical confirmation of the disease 6.