Ultrasound-guided fine-needle aspiration biopsy of thyroid nodules <10 mm in the maximum diameter: does size matter?

Objective: Ultrasound-guided fine-needle aspiration biopsy (US-FNAB) is a safe and effective method of screening malignant thyroid nodules such as papillary thyroid carcinoma. However, not much data are available regarding the diagnostic efficacy of US-FNAB for papillary thyroid microcarcinoma (<= 10 mm in diameter). We aim to compare the diagnostic efficacy of US-FNAB on thyroid nodules between two groups divided by a diameter of 10 mm by correlating the cytological results of US-FNAB with the histopathologic diagnoses in selected patients. Patients and methods: Eight hundred twenty-two thyroid nodules (Group A: diameter <= 10 mm, n=620; Group B: diameter >10 mm, n=202) from 797 patients treated between March 2014 and June 2017 were retrospectively evaluated. Only nodules with Thyroid Imaging Reporting and Data System (TIRADS) categories 4-6 were enrolled and sampled by US-FNAB, followed by surgical resection. Results: According to The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) diagnostic categories, 94 thyroid nodules were classified as I, III and IV, and were excluded from the analysis. The resultant 728 thyroid nodules from 721 patients were analyzed. The malignant tendency (TBSRTC V and VI) rates on US-FNAB were 88.2% and 84.6% (P=0.202) in Group A and Group B, respectively, and the malignant rates were 89.5% and 86.9% (P=0.330), respectively, on histopathology. There was a high concordance between cytology and histopathology diagnoses (kappa value =0.797), and no statistical difference in terms of US-FNAB accuracy was found between the two groups (P=0.533). Conclusion: For thyroid nodules of TIRADS category 4-6, the diagnostic efficacy of US-FNAB is similar for thyroid nodules either smaller or greater than 10 mm in their maximum diameter.