# Eu Tirads Classifier > EU-TIRADS Thyroid Nodule Classifier - Skill: `dromlakhani/eu-tirads-classifier` (Agent Skill) - Install (CLI): `npx skillmds@latest add dromlakhani/eu-tirads-classifier` - Raw SKILL.md: https://api.skillmd.com/api/skills/dromlakhani/eu-tirads-classifier/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: dromlakhani (https://skillmd.com/u/dromlakhani) - Updated: 2026-09-21 - Page: https://skillmd.com/skills/dromlakhani/eu-tirads-classifier --- # EU-TIRADS Thyroid Nodule Classifier **Source:** 2023 ETA Clinical Practice Guidelines for Thyroid Nodule Management. Durante C et al. *European Thyroid Journal* 12:5 e230067. DOI: 10.1530/ETJ-23-0067 --- ## STEP 1 — Examine the Ultrasound Image When a thyroid US image is shared, systematically assess and explicitly report each of the following. Do not skip any feature — the classification depends on a complete set. --- ### A. CONFIRM WHAT YOU ARE LOOKING AT - Is this a thyroid ultrasound? (Confirm the gland is visible — look for the butterfly-shaped structure in the anterior neck) - Which lobe? (Right / Left / Isthmus) - Is the nodule clearly demarcated from the surrounding parenchyma? - Are there one or multiple nodules? (If multiple, focus on the most suspicious one and the largest one — they may differ) --- ### B. NODULE SIZE Measure (or estimate) in **three dimensions**: - Maximum diameter (the most important for FNA threshold decisions) - If the image shows calipers, read them precisely - Report: ___ mm × ___ mm × ___ mm; largest diameter = ___ mm --- ### C. COMPOSITION Assess what proportion of the nodule is solid vs. cystic: | Finding | What to look for | Category | |---|---|---| | **Pure cyst** | Completely anechoic (black), no solid component, thin walls, posterior acoustic enhancement | → Points to EU-TIRADS 2 | | **Spongiform** | Entirely composed of multiple tiny cysts (sponge-like), >50% of volume is microcystic | → Points to EU-TIRADS 2 | | **Mixed cystic-solid** | Has both solid and cystic portions; solid component must be evaluated for high-suspicion features | → Evaluate solid component | | **Predominantly solid** | Solid tissue >50%; higher ROM than mixed lesions | → Evaluate echogenicity and features | > ⚠️ A nodule with **minimal cystic change** (small cysts <50% volume) has a higher ROM than predominantly cystic lesions. Classify by the solid component. --- ### D. ECHOGENICITY OF THE SOLID COMPONENT Compare the solid component to the **normal thyroid parenchyma** (mid-grey reference) and to the **strap muscles** (very dark reference): | Grade | What you see | Clinical meaning | |---|---|---| | **Hyperechoic** | Brighter (whiter) than normal thyroid tissue | Low suspicion | | **Isoechoic** | Same brightness as normal thyroid tissue | Low-intermediate suspicion | | **Mildly hypoechoic** | Darker than normal thyroid, but **lighter than strap muscles** | Intermediate suspicion → EU-TIRADS 4 | | **Markedly hypoechoic** | **As dark or darker than strap muscles** | HIGH suspicion feature → EU-TIRADS 5 | > ⚠️ This is the single most commonly misapplied feature. Use the strap muscles as the anchoring reference for "marked" hypoechogenicity, not the parenchyma. --- ### E. FEATURES OF HIGH SUSPICION (EU-TIRADS 5 determinants) Check each one carefully. **Even ONE present = EU-TIRADS 5.** #### 1. Marked hypoechogenicity - Solid component is as dark or darker than the strap muscles - Distinguished from "mild" hypoechogenicity by comparison to strap muscle, not parenchyma #### 2. Irregular shape - Non-oval, non-round outline - Taller-than-wide (anteroposterior diameter > transverse diameter) — this is a key sign - Irregular or angular outline - Normal: oval or round #### 3. Irregular margins Look carefully at the nodule border. Suspicious patterns: - **Spiculated** — radiating spike-like projections into surrounding tissue - **Lobulated / microlobulated** — scalloped or bumpy border - **Ill-defined** — border cannot be clearly traced - Normal/benign: smooth, well-defined, thin halo (hypoechoic rim = peripheral vascularity) > ⚠️ A thin, regular halo around a nodule is a **non-suspicious** feature associated with benignity. Do not confuse this with an irregular margin. #### 4. Microcalcifications - Punctate echogenic (bright white) foci **<1 mm** in diameter - **No posterior acoustic shadow** (this distinguishes them from macrocalcifications) - Often appear as tiny sparkling dots within the solid component - May be numerous or just 2–3 - Distinguished from: - **Macrocalcifications**: >1 mm, produce posterior shadow, associated with benign involuted nodules (rim calcification) — non-suspicious - **Comet-tail artifact**: echogenic foci with ring-down artifact — seen in colloid, benign --- ### F. EXTRATHYROIDAL EXTENSION SIGNS (check the capsule and surrounding tissue) - **Capsular bulging**: nodule pushes outward against the thyroid capsule - **Capsular disruption**: break in the thyroid capsule continuity - **Abutment**: nodule is directly abutting the capsule without intervening parenchyma - **Tracheal or oesophageal contact**: nodule touches or indents adjacent structures > These features are NOT part of EU-TIRADS scoring, but they mandate FNA regardless of the TIRADS category. --- ### G. CERVICAL LYMPH NODES (if visualised) Look at the lateral and central neck compartments. Suspicious LN features: - **Cystic areas** within the node - **Microcalcifications** in the node - **Thyroid tissue-like appearance** (isoechoic to thyroid) - **Anarchic vascularity** (peripheral or chaotic, without a visible fatty hilum) - Loss of the normal hyperechoic fatty hilum - Round shape (L/S ratio <2) > Suspicious LN → FNA of the node with Tg washout (differentiated thyroid cancer) or calcitonin washout (medullary). --- ## STEP 2 — Assign EU-TIRADS Category Work top-to-bottom. Stop at the first match. | Category | Risk | Defining features | ROM | |---|---|---|---| | **EU-TIRADS 1** | Normal | No nodule seen | None | | **EU-TIRADS 2** | Benign | Pure cyst OR entirely spongiform OR isoechoic/hyperechoic solid nodule with **zero** high-suspicion features | 0% | | **EU-TIRADS 3** | Low risk | Isoechoic or hyperechoic (solid or mixed), **zero** high-suspicion features | 2–4% | | **EU-TIRADS 4** | Intermediate risk | **Mildly hypoechoic** solid component, **zero** high-suspicion features | 6–17% | | **EU-TIRADS 5** | High risk | **ANY ONE** of: irregular shape, irregular margins, microcalcifications, marked hypoechogenicity | 26–87% | ### Classification Decision Rules 1. **EU-TIRADS 2 vs 3**: Both are isoechoic/hyperechoic and have no high-suspicion features. The distinction is composition — EU-TIRADS 2 requires a pure cyst or spongiform appearance. A solid isoechoic nodule with no suspicious features = EU-TIRADS 3. 2. **EU-TIRADS 3 vs 4**: The sole distinguishing feature is echogenicity. Isoechoic/hyperechoic = 3. Mildly hypoechoic = 4. Both require zero high-suspicion features. 3. **EU-TIRADS 4 vs 5**: Mildly hypoechoic + no suspicious features = 4. ANY suspicious feature present (including only microcalcifications, regardless of echogenicity) = 5. 4. **Uncertainty rule**: If you cannot confidently determine whether a suspicious feature is present → classify as **EU-TIRADS 4**, not EU-TIRADS 3. 5. **Mixed cystic-solid EU-TIRADS 5**: Irregular shape, irregular margins, or microcalcifications in the solid component of a partially cystic nodule still qualifies as EU-TIRADS 5. --- ## STEP 3 — Apply FNA Size Threshold | EU-TIRADS | FNA if size... | If below threshold | |---|---|---| | **2** | Never (unless scheduled for treatment/ablation) | Clinical surveillance only | | **3** | **>20 mm** | 5–10 mm: no further evaluation needed; 10–20 mm: repeat US in 3–5 years | | **4** | **>15 mm** | <15 mm: re-evaluate in 1 year | | **5** | **>10 mm** | 5–10 mm: re-evaluate every 6–12 months | ### FNA Override Conditions — Biopsy regardless of size or EU-TIRADS: - Suspicious cervical lymph nodes present → FNA the lymph node (not necessarily the primary nodule) - Signs of extra-thyroidal extension (capsular disruption, abutment) - EU-TIRADS 5 nodule 5–10 mm **with** suspicious lymph nodes or suspected ETE - Patient scheduled for thyroid or parathyroid surgery (pre-operative staging) - Family history of medullary thyroid cancer or MEN2 (calcitonin elevation → consider FNA irrespective of US) ### Withhold FNA if: - **Subnormal TSH** → perform scintigraphy first. Hyperfunctioning (hot) nodules are extremely rarely malignant; FNA should be avoided unless there is high clinical suspicion - Severe coagulopathy (INR ≥3 is an absolute contraindication; antiplatelet therapy is not a contraindication) - EU-TIRADS 2 nodule at any size (unless treatment-related) --- ## STEP 4 — Communicate the Result Structure your output as: **1. Image findings:** List every feature assessed (composition, echogenicity, shape, margins, calcifications, capsule, lymph nodes) with your finding for each. **2. EU-TIRADS classification:** State the category and the ROM range (e.g., "EU-TIRADS 4 — intermediate risk, ROM 6–17%"). **3. FNA recommendation:** - **FNA: YES** — state the indication clearly - **FNA: NO** — state size threshold not met and recommended surveillance interval - **FNA: CONSIDER** — state the clinical override (e.g., suspicious lymph node) **4. Next step:** One clear sentence on what happens next (e.g., "Refer for US-guided FNA" / "Schedule US in 12 months" / "Scintigraphy before biopsy decision"). --- ## CLINICAL GUARDRAILS **What EU-TIRADS was designed for — and its limits:** - Designed and validated primarily for **papillary thyroid carcinoma (PTC)** — sensitivity is high for classical PTC but substantially lower for follicular variant PTC, follicular thyroid carcinoma (FTC), and Hürthle cell carcinoma - Medullary thyroid carcinoma identification is debated; do not rely on EU-TIRADS alone when MTC is clinically suspected **Common classification mistakes:** - Misgrading echogenicity — always use strap muscles as the reference for "marked" hypoechogenicity - Calling benign comet-tail artifacts (colloid crystals) as microcalcifications — look for the ring-down artifact that distinguishes them - Ignoring extrathyroidal features because the TIRADS score is low — capsular signs and lymph node findings override everything - Classifying a solid isoechoic nodule as EU-TIRADS 2 — EU-TIRADS 2 requires a pure cyst or spongiform composition **Multinodular goiter:** - If multiple nodules are present, classify and report: (a) the nodule with the highest EU-TIRADS score, and (b) the largest nodule if different - The propensity to recommend surgery increases with the number of suspicious nodules in a lobe **After FNA — when to repeat:** - Non-diagnostic result → repeat FNA - Bethesda III (AUS/FLUS) → repeat FNA - Discordance between high EU-TIRADS (e.g. 5) and benign cytology (Bethesda II) → repeat FNA - Significant nodule growth (≥20% increase in at least 2 diameters with minimum 2 mm increment, or volume increase >50%) → repeat FNA regardless of prior cytology **Significant growth definition:** ≥20% increase in at least 2 nodule diameters with a minimum increment of 2 mm, OR nodule volume increase >50% — whichever occurs first at follow-up imaging.