Diagnostic challenges in thyroid cytopathology

Fine needle aspiration (FNA) is a long-standing modality used to obtain diagnostic material from patients with thyroid nodules. However, some common and uncommon situations exist in which diagnostic categorization of an FNA specimen is not straightforward. Diagnostically challenging thyroid lesions are typically either benign entities with cytomorphology that mimics malignancy, or malignant entities with unusual cytomorphology that causes difficulty in classification. Awareness of such diagnostic challenges can help broaden one's differential diagnosis when encountering such lesions on FNA. However, in many instances a definitive diagnosis may not be possible and providing an indeterminate diagnosis is most appropriate.