What is the role of neck ultrasound in diagnosing primary hyperparathyroidism (PHPT)?

Neck Ultrasound for Primary Hyperparathyroidism

Neck ultrasound is a highly appropriate initial imaging modality for preoperative localization in primary hyperparathyroidism, with reported sensitivity of 76-80% and positive predictive value of 93-95%, and should be combined with sestamibi scintigraphy with SPECT/CT to maximize localization accuracy. 1

Role of Ultrasound in PHPT

Diagnostic Limitations

• Ultrasound has no role in confirming or excluding the diagnosis of PHPT, which must be made biochemically with serum calcium and PTH levels. 2, 3
• Imaging is exclusively for preoperative localization to facilitate minimally invasive parathyroidectomy (MIP), not for diagnosis. 1, 2

Performance Characteristics for Localization

Single-Gland Disease:

• Sensitivity ranges from 76-80% in meta-analyses, though individual studies report wide variability (44-97%). 1
• Positive predictive value is consistently high at 93-95%. 1, 4
• Detection rate reaches 96% for single parathyroid adenomas when performed by experienced operators. 5

Factors Affecting Detection:

• Adenomas located caudally (inferior pole) have 92% detection rate, while cranially located adenomas have only 23% detection rate. 6
• Color Doppler identification of feeding vessels increases diagnostic accuracy to 93% versus only 39% when vessels are not detected. 6
• Larger adenomas are detected more reliably; sensitivity decreases significantly with smaller glands. 4, 7

Common Causes of False-Negative Results

Ultrasound fails to localize adenomas most commonly due to: 1

• Ectopic location (mediastinal, intrathymic)
• Far posterior positioning behind thyroid
• Multigland disease (MGD affects 15-20% of PHPT cases)
• Small adenoma size (<1 cm)
• Concomitant thyroid disease obscuring visualization

Recommended Imaging Strategy

Initial Imaging Approach

The combination of ultrasound and sestamibi scintigraphy with SPECT/CT achieves the highest diagnostic performance, with sensitivity of 93-96.8% and PPV of 95.8-96%. 1, 2, 4

• Both the American Head and Neck Society and American Association of Endocrine Surgeons recommend ultrasound as the preferred initial study, noting the advantage of concurrent thyroid evaluation. 1
• Multiple imaging modalities used in combination maximize accuracy through concordant results. 1
• Approximately 60% of PHPT patients have concomitant nodular thyroid disease requiring evaluation. 4

Alternative Imaging When Ultrasound is Inadequate

4-D parathyroid CT (multiphase CT without and with IV contrast) is the primary alternative, with sensitivity of 79-92% for single-gland disease and PPV of 88-92%. 1, 2

• CT is particularly valuable for ectopic adenomas in the root of neck and mediastinum. 5
• Most studies show CT performance superior to ultrasound alone, though one prospective study found dual-isotope scintigraphy superior to CT. 1

Operator Expertise Considerations

• Ultrasound performed by experienced endocrinologists or surgeons achieves sensitivity of 85-87% with PPV of 95.2%. 4, 7
• Surgeon-performed ultrasound with correct localization results in shorter operative times (60 vs 80 minutes), fewer bilateral neck explorations (8% vs 39%), and lower operative failure rates (0.3% vs 9.6%). 7
• Younger patients (<60 years) have higher rates of correct ultrasound localization. 7

Clinical Implications for Surgical Planning

When Ultrasound Enables MIP

Concordant preoperative imaging (ultrasound + sestamibi) identifying a single adenoma allows MIP in approximately 80% of PHPT cases, offering faster recovery and decreased costs. 2

• Intraoperative PTH monitoring is mandatory during MIP to confirm adequate resection. 2
• Unilateral neck exploration is sufficient in approximately 90% of patients with correct ultrasound localization. 6

When Bilateral Neck Exploration is Required

BNE remains necessary when: 2

• Preoperative imaging is discordant or nonlocalizing
• High suspicion for multigland disease (15-20% of cases)
• Ultrasound negative or equivocal findings

Recurrent or Persistent PHPT

• In reoperative cases, ultrasound sensitivity data is limited in the provided guidelines. 1
• Multiple imaging modalities should be combined to maximize localization confidence after failed initial surgery. 1
• CT and MRI become more important in the reoperative setting, with MRI showing 82-93% sensitivity. 1