TI-RADS Guidelines for Thyroid Nodule Assessment and Management
The American College of Radiology (ACR) Thyroid Imaging Reporting and Data System (TI-RADS) is the recommended standardized system for categorizing thyroid nodules based on ultrasound features to guide management decisions regarding fine-needle aspiration (FNA) and follow-up. 1
TI-RADS Classification System
TI-RADS categorizes thyroid nodules into six risk levels:
| Category | Description | Risk of Malignancy |
|---|---|---|
| TI-RADS 1 | Non-diagnostic/Unsatisfactory | - |
| TI-RADS 2 | Benign | <2% |
| TI-RADS 3 | Atypia of undetermined significance | 2-5% |
| TI-RADS 4 | Follicular neoplasm | 5-50% (4A), 50-90% (4B/4C) |
| TI-RADS 5 | Suspicious for malignancy | ≥90% |
Ultrasound Features Assessment
The ACR TI-RADS evaluates nodules based on these key ultrasound characteristics:
- Shape: Taller-than-wide shape increases suspicion for malignancy 2
- Border: Obscure or irregular borders suggest higher risk 2
- Margin: Irregular margins are concerning 2
- Internal content: Solid nodules have higher risk than cystic ones 2
- Echogenicity: Marked hypoechogenicity and hypoechogenicity increase risk 2
- Calcifications: Microcalcifications are associated with malignancy 2
- Vascularity: Internal vascularization distribution is concerning 2
Management Recommendations Based on TI-RADS Category
FNA Recommendations
- TI-RADS 2 (Benign): No FNA required regardless of size 1
- TI-RADS 3 (Low suspicion): FNA if ≥1.5 cm; follow-up at 6-12 months if ≥1.5 cm but no FNA performed 1
- TI-RADS 4 (Intermediate suspicion): FNA if ≥1.0 cm 1
- TI-RADS 5 (High suspicion): FNA if ≥1.0 cm 1
Follow-up Recommendations
- TI-RADS 3 nodules ≥1.5 cm: Initial ultrasound follow-up at 6-12 months; if stable for 1-2 years, follow-up intervals can be extended or discontinued 1
- TI-RADS 3 nodules <1.5 cm: No routine follow-up required unless clinical concerns arise 1
- Nodule growth (>20% increase in two dimensions with minimum 2mm increase): Consider FNA 1
Clinical Risk Factors to Consider
Certain clinical factors increase suspicion for malignancy and may influence management decisions:
- History of head and neck irradiation
- Family history of thyroid cancer
- Associated syndromes (MEN2, familial adenomatous polyposis)
- Age <20 or >70 years
- Male sex
- Rapid nodule growth
- Compressive symptoms
- Hard or fixed nodule
- Presence of cervical adenopathy 1
Diagnostic Accuracy and Limitations
- TI-RADS has demonstrated high sensitivity (76%) and specificity (97.5%) for detecting malignancy in high-suspicion nodules 3
- Comparable performance to ATA guidelines (sensitivity 80%, specificity 96.3%) 3
- Positive predictive value is moderate (63.3% for TI-RADS) 3
Important Considerations and Pitfalls
- Small (<1.5 cm) TI-RADS 4 and 5 nodules that don't meet size criteria for FNA may still harbor malignancy (5.7% and 25.0% risk, respectively) 4
- Most malignant nodules missed by ACR TI-RADS are either recommended for ultrasound follow-up or are smaller than 1 cm 5
- FNA has limitations including false-negative results (up to 5%) and difficulty in definitively diagnosing follicular lesions 1
- Molecular diagnostics may be useful for reclassifying indeterminate nodules (follicular neoplasm, atypia of undetermined significance) 6
Integration with Other Classification Systems
- FNA results are typically categorized according to the Bethesda System for Reporting Thyroid Cytopathology 1
- TI-RADS score 3 nodules have shown high negative predictive values (94.6%) compared with Bethesda scoring 4
- For surgical planning, total thyroidectomy is recommended if malignancy is confirmed in bilateral nodules 1
The ACR TI-RADS system provides a standardized approach to thyroid nodule evaluation that helps reduce unnecessary biopsies while maintaining high sensitivity for detecting clinically significant thyroid malignancies.