Reliability of benign fine needle aspiration cytology of large thyroid nodules.

BACKGROUND: With increasing use of thyroid ultrasonography, thyroid nodules have been found to be extremely common. For over 25 years, fine needle aspiration (FNA) has been the pivotal diagnostic test to discriminate benign from potentially malignant thyroid nodules. Recently, false negative rates exceeding 10% have led to recommendations that thyroid nodules >/=4 cm should be resected regardless of cytology results. Our aim was to determine the false negative rate of FNA cytology on thyroid nodules >/=3 cm interpreted as benign at our institution. METHODS: A retrospective review was performed at Mayo Clinic from January 2002 through December 2006. RESULTS: From 6,921 ultrasonographic-guided thyroid FNAs, 742 were interpreted as benign and >/=3 cm. A definitive histologic diagnosis was available for 145 (20%) patients who underwent thyroidectomy: 1 (0.7%) was false negative. No additional thyroid malignancies were identified in 550 index nodules with average follow-up of 3 years. CONCLUSION: With precise ultrasonographic-guided aspiration, strict adherence to guidelines for adequacy of the sample, proper cytologic preparation, and most importantly, expert cytologic analysis, a diagnosis of benign is extremely reliable for thyroid nodules, regardless of size. Resection for diagnosis is not necessary, and a size >/=3 cm should not be an independent indication for resection.