Subtitle: The Bethesda System for Reporting Thyroid Cytopathology, 3rd edition (2023): the six categories with new names, adequacy criteria, risk of malignancy, management, molecular testing, NIFTP and 8 MCQs.
Author: PathologyMCQ Editorial Board
Category: Endocrine Pathology
Last Updated: October 2026
Read Time: 6 minutes
At-a-Glance
- Six categories, each with a single name in the 3rd edition.
- AUS replaces AUS/FLUS; follicular neoplasm replaces “suspicious for follicular neoplasm”.
- Adequacy: ≥6 groups of ≥10 well-preserved follicular cells, with defined exceptions.
- Risk of malignancy now quoted as a mean with range; separate figures for children.
- Molecular testing is built into management of Bethesda III–V.
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The Six Categories
| Category | Mean ROM (range) | Usual management |
|---|---|---|
| I. Nondiagnostic | 13% (5–20%) | Repeat FNA with ultrasound guidance |
| II. Benign | 4% (2–7%) | Clinical and ultrasound follow-up |
| III. Atypia of undetermined significance (AUS) | 22% (13–30%) | Repeat FNA, molecular testing, diagnostic lobectomy or surveillance |
| IV. Follicular neoplasm | 30% (23–34%) | Molecular testing, diagnostic lobectomy |
| V. Suspicious for malignancy | 74% (67–83%) | Molecular testing, lobectomy or near-total thyroidectomy |
| VI. Malignant | 97% (97–100%) | Lobectomy or near-total thyroidectomy |
Typical cytology: benign = colloid, macrofollicle fragments, thyroiditis; AUS = focal nuclear atypia or architectural atypia not enough for higher categories; FN = cellular, microfollicles, scant colloid, no PTC nuclei; V and VI = PTC nuclear features, medullary carcinoma, anaplastic carcinoma, lymphoma or metastasis.
Adequacy Criteria
- At least 6 groups of well-visualised follicular cells, each with ≥10 cells, preferably on one slide.
- Exceptions (no minimum cell count): solid nodules with atypia (report in III–VI), thyroiditis (lymphocytic, granulomatous, abscess) and abundant thick colloid (benign).
- Cyst fluid only with macrophages: nondiagnostic (cyst fluid only).
What Changed in 2023
- Single names for every category; “FLUS” and “suspicious for” follicular neoplasm dropped.
- AUS subcategorised as AUS-nuclear or AUS-other (higher risk with nuclear atypia).
- Oncocytic (Hürthle cell) neoplasm reported as follicular neoplasm, oncocytic type.
- Separate ROM for paediatric nodules, which is higher.
- Aligned with WHO 2022 terminology, including NIFTP and high-grade follicular-derived carcinoma.
Image MCQ
Answer: C. An adequate thyroid FNA needs at least 6 groups of well-visualised follicular cells, each with at least 10 cells. No minimum is needed for solid nodules with atypia, thyroiditis or nodules with abundant colloid.
Test Yourself: 8 MCQs
Bethesda 2023: 8 MCQs
Categories, adequacy, risk of malignancy and management, with instant explanations.
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Exam Pearls
- 6 × 10 adequacy rule, with three exceptions.
- III = AUS; IV = follicular neoplasm.
- ROM: 13, 4, 22, 30, 74, 97%.
- Molecular testing for III–V.
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References
- Ali SZ, VanderLaan PA, eds. The Bethesda System for Reporting Thyroid Cytopathology. 3rd ed. Springer; 2023.
- Ali SZ, et al. The 2023 Bethesda System for Reporting Thyroid Cytopathology. Thyroid. 2023;33:1039–44.
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