Hürthle cell lesions of the thyroid: Progress made and challenges remaining

Hürthle cell–predominant thyroid fine needle aspirations (FNA) are encountered frequently in routine practice, yet they are often challenging to diagnose accurately and are associated with significant interobserver variability. This is largely due to the ubiquity of Hürthle cells in thyroid pathology, ranging from nonneoplastic conditions to aggressive malignancies. Although limitations in cytomorphologic diagnoses likely will remain for the foreseeable future, our knowledge of the molecular pathogenesis of Hürthle cell neoplasia and application of molecular testing to cytologic material have increased dramatically within the past decade. This review provides context behind the challenges in diagnosis of Hürthle cell lesions and summarizes the more recent advances in diagnostic tools. Diagnosis of Hürthle cell neoplasia is one of the most challenging areas of thyroid fine‐needle aspiration cytology. This review describes the current state of the art in the cytology of Hürthle cell lesions as well as the clinical, histologic, and molecular findings associated with Hürthle cell tumors.