What should be assessed on ultrasound to diagnose primary hyperparathyroidism?

Ultrasound Assessment for Primary Hyperparathyroidism

Ultrasound assessment for primary hyperparathyroidism should focus on identifying enlarged parathyroid glands with specific sonographic characteristics, though it should be performed only after biochemical confirmation of the disease. 1

Important Preliminary Considerations

• The diagnosis of primary hyperparathyroidism is biochemical (elevated or high-normal serum calcium with concurrent elevated or inappropriately normal PTH levels), not radiological 1
• Imaging studies, including ultrasound, have no role in confirming or excluding the diagnosis but are used for preoperative localization after biochemical confirmation 1
• Ultrasound is often used as an initial imaging study due to its low cost, wide availability, and non-invasive nature 2

Key Ultrasound Features to Assess

B-Mode (Grayscale) Assessment

• Look for enlarged oval or bean-shaped hypoechoic nodules posterior to the thyroid gland 2
• Assess for typical locations: posterior to upper and lower poles of thyroid gland 3
• Evaluate for ectopic locations: thyrothymic ligament, carotid sheath, mediastinum, or intrathyroidal 4
• Measure dimensions of suspected parathyroid adenomas (typically >5mm in diameter) 5
• Assess for homogeneous texture which helps differentiate from thyroid nodules 2

Vascular Assessment

• Identify polar feeding artery using color Doppler, which is characteristic of parathyroid adenomas 2
• Evaluate for peripheral vascularity pattern which helps differentiate from lymph nodes 2

Advanced Ultrasound Techniques

• Consider shear wave elastography (SWE) which shows parathyroid adenomas typically have lower tissue stiffness compared to thyroid tissue 2
• 3D ultrasound technology can enhance visualization of the polar artery when adding 3D color Doppler 2

Potential Pitfalls and Challenges

• Concomitant thyroid nodules significantly decrease ultrasound sensitivity (from 94-100% without thyroid nodules to 54-84% with thyroid nodules) 6
• Smaller adenomas (<5mm) are more difficult to detect 5
• Ectopic parathyroid glands are often missed on ultrasound 3, 4
• Intrathyroidal parathyroid adenomas can be misdiagnosed as thyroid nodules 4
• Distinguishing parathyroid adenomas from level 6 lymph nodes can be challenging 2

Improving Diagnostic Accuracy

• Combining ultrasound with other imaging modalities (such as sestamibi scanning) increases sensitivity and positive predictive value 3, 7
• Per-patient sensitivity and positive predictive values are approximately 84% and 99% for ultrasound alone, but increase to 91% and 98% when combined with scintigraphy 4
• Office-based ultrasound performed by experienced clinicians can localize abnormal glands to the specific quadrant in approximately 79% of cases 7

Special Considerations for Secondary and Tertiary Hyperparathyroidism

• Secondary and tertiary hyperparathyroidism typically involve multiglandular disease (MGD) 3
• The goal of imaging in these cases is to identify all eutopic and potential ectopic or supernumerary glands 3
• Ultrasound sensitivity for detecting ectopic glands in secondary/tertiary hyperparathyroidism is lower (7-32%) 3