Clear-cell change in follicular adenoma mimicking Hürthle-cell tumor on thyroid aspiration biopsy cytology.

We present a case of follicular adenoma with clear-cell change, which on fine-needle aspiration biopsy mimicked a Hürthle-cell tumor. Papanicolaou-stained smears revealed a monomorphic pattern of loosely cohesive groups of cells with abundant cytoplasm and centrally placed round nuclei with single prominent nucleoli. The cytoplasm was granular or finely vacuolated with occasional intracytoplasmic brown pigment. Subsequent surgical histology of the partial thyroidectomy specimen revealed a follicular adenoma composed of macro- and microfollicles. The microfollicular areas showed clear-cell change: these cells appeared identical to those seen on cytology. No Hürthle-cell change was present in the surgical specimen. Follicular cells with clear-cell change of the granular type must be added to the list of differential diagnoses when cells with Hürthle-like features are seen on aspiration biopsy of the thyroid.