How to Follow Fine-Needle Aspiration Biopsy-Confirmed Benign Thyroid Nodules

For patients with initially benign cytological results, the American Thyroid Association (ATA) clinical guidelines suggest ultrasound monitoring for more than 24 months for very-low-suspicion nodules, and 12–24 months for low-to-intermediate-suspicion nodules, and ultrasound monitoring and/or fine-needle aspiration (FNA) biopsy within 12 months for high-suspicion nodules [1]. Although accurate estimation of risk of malignancy (ROM) for cytological benign nodules is difficult because only a small fraction undergo surgery (causing selection bias and overestimation), it was estimated as 0-3% by the Bethesda system [2, 3, 4], as 1–2% in patients with systemic repeat FNA in nodules with prior benign cytology [5, 6], and as 3.2% of 4055 patients with benign cytology who underwent surgery [7]. However, higher ROMs have been reported in several other studies with meta-analyses: 3.7% by Bongiovanni et al., 4–9% by Sheffield et al., and 9.0 (1.1–32.2) % by Ohori and Schoedel [8, 9, 10]. Although false negatives in FNA diagnosis depend on multiple factors, such as sampling technique, nature of the nodule (fibrotic, calcified, cystic, or size of nodule), experience of interpreters, morphological criteria of FNA diagnoses, and method of handling incidental carcinomas, the author of this chapter believes it is of paramount importance to minimize false-negative results (ROMs for benign nodules) to the 0–3% level implied by the Bethesda system, which will establish trust between cytopathologists and clinical colleagues, as well as improve performance in thyroid FNA practice. For further analysis of false-positive diagnoses, please refer to Chap. 2, and for cytology laboratory quality control and how to monitor practice, please refer to Chap. 66.