Ata Thyroid Fna Decision

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name: ata-thyroid-fna-decision
description: Decides whether a thyroid nodule needs FNA biopsy using the ATA 2015 sonographic pattern classification (high/intermediate/low/very low/benign) and nodule size thresholds. Use when a clinician asks "does this thyroid nodule need a biopsy", "should I FNA this nodule", "what size threshold for thyroid FNA", "is this nodule suspicious enough for biopsy", or describes a thyroid ultrasound finding and wants a biopsy recommendation. Distinct from EU-TIRADS — uses the ATA 5-pattern system.
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# 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

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## 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

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## 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.

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## 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% |

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## 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%)

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## 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.

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## 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

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## 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