Thyroid cytology: challenges in the pursuit of low-grade malignancies

Detection of thyroid cancer is challenging for several reasons. Although thyroid nodules are common, most are benign. Furthermore, most thyroid cancers are low grade and share pathologic features with benign nodules. Because of these overlapping characteristics and the challenges in performing fine needle aspiration, many cytology cases result in an indeterminate or unsatisfactory diagnosis. This article describes the pathologic features of thyroid nodules, the challenges in obtaining a diagnostic specimen, and the reporting of thyroid lesions using the Bethesda classification system for thyroid cytopathology. The role of molecular and other ancillary studies in refining diagnostic practice is also examined.