TI-RADS 3 Nodule FNAC Criteria
For TI-RADS 3 (mildly suspicious) thyroid nodules, fine-needle aspiration cytology is recommended when the nodule measures ≥2.5 cm, while nodules <2.5 cm should undergo ultrasound surveillance rather than immediate biopsy. 1
Size-Based FNA Thresholds for TI-RADS 3 Nodules
The critical size threshold for TI-RADS 3 nodules is 2.5 cm. 1 This recommendation balances the low malignancy risk of mildly suspicious nodules against the need to detect clinically significant cancers.
- Nodules ≥2.5 cm: Proceed with ultrasound-guided FNA biopsy 1
- Nodules 1.5-2.4 cm: Ultrasound surveillance is recommended rather than immediate FNA 1
- Nodules <1.5 cm: No FNA indicated; surveillance only 1
The rationale is that TI-RADS 3 nodules carry a low cancer risk, with negative predictive values of 94.6% for benign disease 2. Research demonstrates that lowering the size threshold from 1.5 cm to 1.0 cm for TI-RADS 3 nodules would capture only 7 additional malignant nodules but would add 118 benign nodules to follow-up, representing an unfavorable risk-benefit ratio 3.
High-Risk Clinical Features That Lower the FNA Threshold
Even for TI-RADS 3 nodules <2.5 cm, FNA should be considered when specific high-risk clinical factors are present: 1
- History of head and neck irradiation - substantially increases baseline malignancy risk 1
- Family history of thyroid cancer - particularly medullary thyroid carcinoma or familial syndromes 1
- Suspicious cervical lymphadenopathy - suggests possible nodal metastases 1
- Subcapsular location - increases risk of extrathyroidal extension 1
These clinical contexts modify the pretest probability sufficiently to warrant tissue diagnosis despite the lower TI-RADS score.
Ultrasound Features Defining TI-RADS 3
TI-RADS 3 nodules typically have mildly suspicious sonographic characteristics but lack the multiple high-risk features seen in TI-RADS 4-5 categories. 1 Common patterns include:
- Solid composition with isoechoic or mildly hypoechoic appearance 1
- Smooth or mostly smooth margins 1
- Absence of microcalcifications 1
- No evidence of extrathyroidal extension 1
Surveillance Protocol for TI-RADS 3 Nodules Not Meeting FNA Criteria
For TI-RADS 3 nodules <2.5 cm without high-risk features, ultrasound surveillance is the appropriate management: 1
- Initial follow-up ultrasound at 12 months 1
- Subsequent surveillance intervals based on stability 1
- FNA should be performed if the nodule grows ≥20% in two dimensions with a minimum increase of 2 mm 1
Critical Pitfalls to Avoid
Do not perform FNA on TI-RADS 3 nodules <2.5 cm without high-risk features. This leads to overdiagnosis and overtreatment of clinically insignificant cancers, particularly papillary microcarcinomas that have excellent prognosis with observation alone. 1
Do not rely on thyroid function tests (TSH, T3, T4) to determine malignancy risk. Most thyroid cancers present with normal thyroid function, making these tests unhelpful for risk stratification. 1
Ensure ultrasound guidance for all FNA procedures. Ultrasound-guided FNAB has significantly lower non-diagnostic rates compared to freehand technique and is the preferred diagnostic method for accuracy, economy, and safety. 1, 4
Special Consideration for Subcentimeter TI-RADS 3 Nodules
Research on subcentimeter nodules demonstrates that TI-RADS scores of 1-2 had 0% risk of papillary thyroid carcinoma, while TI-RADS 3 nodules showed intermediate risk. 5 However, even for high-scoring subcentimeter nodules, the current evidence supports surveillance over immediate biopsy unless high-risk clinical features are present. 1, 6
The nondiagnostic rate for subcentimeter nodules (7%) is higher than for larger nodules (3%), further supporting the size-based threshold approach. 5