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Bethesda III Thyroid FNA — RACP Adult Medicine MCQ

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ModerateEndocrinologyBethesda III Thyroid FNARACP Adult Medicine

A 50-year-old woman has a thyroid nodule FNA reported as Bethesda III (atypia of undetermined significance/follicular lesion of undetermined significance). The estimated malignancy risk is 10-30%. What is the most appropriate next step?

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Correct answer: A — Fine needle aspiration biopsy

Bethesda III (AUS/FLUS) has an intermediate malignancy risk (10-30%). Options include repeat FNA in 6-12 weeks (most common), molecular testing (ThyroSeq, Afirma) if available to refine risk, or diagnostic thyroid lobectomy. Repeat FNA reclassifies ~50% of cases into a more definitive category. If repeat FNA remains Bethesda III, diagnostic lobectomy is recommended.

Reference: ATA – 2015 – Thyroid Nodule; Bethesda System 2017