What to do if a suspicious mass is found on a thyroid ultrasound (US)?

Management of Suspicious Thyroid Mass on Ultrasound

Proceed immediately with ultrasound-guided fine-needle aspiration biopsy (FNA) for any thyroid nodule >1 cm with suspicious ultrasound features, as this is the most accurate and cost-effective method for determining malignancy and guiding surgical decisions. 1, 2

Initial Risk Stratification Based on Ultrasound Features

The ultrasound characteristics determine your next steps. Suspicious features that mandate FNA include: 1, 2

• Microcalcifications - highly specific for papillary thyroid carcinoma (specificity 75.9%, OR 7.1) 2
• Marked hypoechogenicity - solid nodules darker than surrounding thyroid parenchyma 1, 2
• Irregular or microlobulated margins - infiltrative borders rather than smooth contours (OR 7.2, specificity 79.6%) 1, 2
• Taller-than-wide shape - strongest predictor of malignancy (OR 13.7, PPV 76.0%) 2
• Absence of peripheral halo - loss of the thin hypoechoic rim normally surrounding benign nodules 1
• Central hypervascularity - chaotic internal vascular pattern rather than peripheral flow only 1

Size-Based FNA Thresholds

For nodules >1 cm: Perform FNA if ≥2 suspicious ultrasound features are present 1, 2

For nodules <1 cm: Perform FNA only if suspicious features are present PLUS high-risk clinical factors (see below) 1, 2

For nodules >4 cm: Perform FNA regardless of ultrasound appearance due to increased malignancy risk 1

High-Risk Clinical Factors That Lower FNA Threshold

These factors warrant FNA even for smaller nodules or those with fewer suspicious features: 1

• History of head and neck irradiation - increases malignancy risk approximately 7-fold 1
• Family history of thyroid cancer - particularly medullary thyroid carcinoma or familial syndromes 1
• Age <15 years or male gender - higher baseline malignancy probability 1
• Rapidly growing nodule - suggests aggressive biology 1
• Firm, fixed nodule on palpation - indicates extrathyroidal extension 1
• Vocal cord paralysis or compressive symptoms - suggests invasive disease 1
• Suspicious cervical lymphadenopathy - warrants immediate FNA 1
• Focal FDG uptake on PET scan - triggers FNA 1

Technical Approach to FNA

Ultrasound guidance is mandatory - it allows real-time needle visualization, confirms accurate sampling, enables marker clip placement, and is superior to palpation-guided biopsy in terms of accuracy, patient comfort, and cost-effectiveness 3, 1, 4

Core needle biopsy is superior to fine-needle aspiration alone for diagnostic accuracy, sensitivity, specificity, and correct histological grading 3, 1

If initial FNA is nondiagnostic: Repeat FNA under ultrasound guidance; if repeat remains nondiagnostic, reassess the number of suspicious ultrasound features and consider core needle biopsy 1

Interpretation Using Bethesda Classification System

The Bethesda System stratifies FNA results into six categories with specific malignancy risks: 1

• Category I (Nondiagnostic): Repeat FNA under ultrasound guidance 1
• Category II (Benign): Very low malignancy risk (1-3%); clinical follow-up appropriate 1
• Category III (AUS/FLUS): Consider molecular testing (BRAF V600E, RET/PTC, RAS, PAX8/PPARγ) or repeat FNA 1
• Category IV (Follicular Neoplasm): Surgery often required for definitive diagnosis; malignancy rate 12-34% depending on subcategory 1
• Category V (Suspicious for Malignancy): Immediate surgical consultation 1
• Category VI (Malignant): Immediate surgical consultation for total or near-total thyroidectomy 1

Additional Diagnostic Considerations

Measure serum calcitonin as part of the diagnostic workup to screen for medullary thyroid cancer, which has higher sensitivity than FNA alone 1

Check TSH levels before FNA - higher TSH levels are associated with increased risk for differentiated thyroid cancer 1

Do not rely on thyroid function tests alone for malignancy assessment, as most thyroid cancers present with normal thyroid function 1

Critical Pitfalls to Avoid

Never override a reassuring FNA when worrisome clinical findings persist - false-negative results occur in up to 11-33% of cases 3, 1

Avoid performing FNA on nodules <1 cm without high-risk features - this leads to overdiagnosis and overtreatment of clinically insignificant cancers 1

Do not use radionuclide scanning in euthyroid patients for determining malignancy - it is not helpful for this purpose 2

Follicular neoplasms may yield indeterminate results requiring surgical excision for definitive diagnosis, as FNA alone cannot distinguish follicular adenoma from carcinoma 1

Surveillance Protocol When FNA Not Immediately Indicated

For nodules not meeting FNA criteria based on size and features: 2

• TR3 nodules (intermediate suspicion): Ultrasound follow-up at 12,24, and 60 months 2
• TR4 nodules (moderately suspicious): Ultrasound follow-up at 12,24, and 60 months 2