The Bethesda Classification for Thyroid Fine Needle Aspiration: A Predictor or an Alarmist?

Thyroid malignancies comprise only 2 per cent of all cancers. Yet the incidence of thyroid cancers has been increasing faster than other malignancies, likely due to increased screening and surveillance of thyroid nodules. The Bethesda system represents the preferred method of evaluating thyroid nodules for malignancy using fine needle aspiration (FNA). Many thyroidectomies are performed for small, asymptomatic nodules found on ultrasound. These small papillary cancers (<0.5 cm) are termed microcarcinomas and represent a more indolent natural history causing some to name them "occult papillary tumors." The objective is to assess the relationship between the Bethesda classification and pathologic stage of thyroid cancer with attention to T1a lesions. A single institution, retrospective study of thyroidectomy patients who had a preoperative FNA and a final pathology of thyroid malignancy were performed. The distribution of stage relative to Bethesda classification was significantly different than expected (P = 0.00382). The low risk Bethesda II, (odds ratio;OR 9.15, 2.7931-29.97, P = 0.0003) and the intermediate group, Bethesda III, (OR 3.48, 1.4436-8.4124, P = 0.0055) had a statistically significant higher incidence of T1a. The Bethesda classification for thyroid FNA falls short in the accuracy of intermediate stage malignancies. Patients whose FNA were Bethesda II or III had a higher likelihood of indolent T1a disease.