dromlakhani ATA Thyroid Nodule FNA Decision Tool
Source: 2015 ATA Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer. Haugen et al. Thyroid 2016;26(1). DOI: 10.1089/thy.2015.0020
STEP 1 — Check TSH First
- TSH subnormal → get radionuclide thyroid scan
- If a hyperfunctioning ("hot") nodule corresponds to the nodule in question → no FNA needed (hot nodules rarely malignant)
- If nodule is iso- or nonfunctioning → proceed to Step 2
- TSH normal or elevated → proceed directly to Step 2
STEP 2 — Perform Thyroid + Neck Ultrasound
Evaluate every nodule for:
- Size (largest dimension)
- Composition (solid, cystic, mixed)
- Echogenicity vs parenchyma
- Margins
- Calcifications
- Shape (taller than wide?)
- Extrathyroidal extension (ETE)
Also survey cervical lymph nodes. If a suspicious LN is found → FNA the lymph node (cytology + Tg washout), regardless of nodule size.
STEP 3 — Classify the Sonographic Pattern
| Pattern | Ultrasound Features | Malignancy Risk |
|---|---|---|
| High suspicion | Solid hypoechoic OR solid hypoechoic component of a partially cystic nodule PLUS ≥1 of: irregular margins (infiltrative/microlobulated), microcalcifications, taller than wide, rim calcifications with extrusive soft tissue component, ETE | >70–90% |
| Intermediate suspicion | Hypoechoic solid nodule with smooth margins, WITHOUT microcalcifications, ETE, or taller than wide shape | 10–20% |
| Low suspicion | Isoechoic or hyperechoic solid nodule, OR partially cystic with eccentric solid areas — WITHOUT microcalcifications, irregular margins, ETE, or taller than wide | 5–10% |
| Very low suspicion | Spongiform or partially cystic nodule WITHOUT any of the above suspicious features | <3% |
| Benign | Purely cystic (no solid component whatsoever) | <1% |
STEP 4 — Apply the FNA Size Threshold
| Pattern | FNA Decision |
|---|---|
| High suspicion | FNA if ≥1 cm |
| Intermediate suspicion | FNA if ≥1 cm |
| Low suspicion | FNA if ≥1.5 cm |
| Very low suspicion | Consider FNA if ≥2 cm — observation without FNA is also reasonable |
| Benign | No FNA (aspiration only if symptomatic/large cyst) |
Focal 18FDG-PET uptake in a nodule ≥1 cm → FNA regardless of sonographic pattern (malignancy risk ~35%)
STEP 5 — If Below Size Threshold (No FNA Today)
Follow up sonographically based on pattern:
| Pattern | Follow-up US interval |
|---|---|
| High suspicion | Repeat US in 6–12 months |
| Low–intermediate suspicion | Repeat US in 12–24 months |
| Very low suspicion | Repeat US at ≥24 months (≤1 cm: no routine follow-up needed) |
| Benign / purely cystic | No follow-up required |
Trigger FNA on follow-up if: ≥20% size increase in two dimensions (with ≥2 mm absolute increase), or new suspicious US feature develops.
STEP 6 — Special Situations
Multiple nodules:
- Evaluate each nodule ≥1 cm independently using its own sonographic pattern and size threshold
- When none has high/intermediate suspicion and similar very-low/low nodules coalesce: aspirate the largest (≥2 cm) or observe
Multinodular goiter with low/low-normal TSH:
- Get radionuclide scan to identify autonomous nodules
- FNA only non-hyperfunctioning nodules that meet high suspicion criteria
Two benign FNA results on same nodule:
- US surveillance for malignancy is no longer indicated — can discharge from further FNA monitoring
CLINICAL GUARDRAILS
- Don't skip TSH — a subnormal TSH changes the entire algorithm (scan first, FNA later or never)
- Don't FNA a hot nodule — hyperfunctioning nodules are almost never malignant; cytologic yield is poor and misleading
- Echogenicity relative to parenchyma, not to muscle — isoechoic vs parenchyma ≠ isoechoic vs strap muscle
- Spongiform ≠ suspicious — the sponge appearance (>50% microcystic by volume) is strongly correlated with benignity; don't over-call it as low suspicion
- Diffuse 18FDG-PET uptake (not focal) usually = Hashimoto's thyroiditis — no FNA required
- Size alone does not trigger FNA — a 3 cm very-low-suspicion spongiform nodule does NOT need FNA; pattern drives the threshold, not size in isolation
- High-risk clinical features (radiation history, familial DTC, hoarseness, lymphadenopathy) lower your threshold — consider FNA at smaller sizes for all patterns in these patients