Fine-needle aspiration of the thyroid: today and tomorrow.

This review describes the morphological features of the common thyroid lesions that are sampled by fine-needle aspiration (FNA), including hyperplastic (adenomatous, adenomatoid) nodules, inflammatory and autoimmune conditions (lymphocytic thyroiditis), and benign and malignant neoplasms. For the last category of lesions, the cytological features are described and the differential diagnoses are discussed. Finally, an assessment of modern techniques such as immunohistochemistry and molecular analyses is given with emphasis on their validity for FNA samples as well as the pitfalls that are encountered in their use.