Ultrasound-guided fine needle aspiration of thyroid nodules: factors affecting diagnostic outcomes and confounding variables.

Background The incidence of thyroid cancer is increasing in men and women. Fine needle aspiration (FNA) is an accepted technique to assess thyroid nodules but is associated with a high rate of non-diagnostic sampling. Purpose To assess the diagnostic performance of ultrasound-guided FNA of thyroid nodules and identify factors associated with non-diagnostic sampling. Material and Methods A retrospective review of thyroid FNAs was performed between 2006 and 2013. Patient demographics, nodule characteristics, procedural technique, cytology, and complications were recorded. Cytology was categorized THY1-5 based on the British Thyroid Association guidelines. Descriptive and multivariable analysis were conducted to identify factors associated with non-diagnostic sampling. Results A total of 724 procedures were identified with 597 (82.5%) in women, and an overall mean age of 40 years (age range, 17-87 years). Factors associated with a non-diagnostic outcome in the multivariable regression analysis included increasing lesion depth (OR, 1.05 per mm; 95% confidence interval [CI], 1.007-1.10), age (OR, 1.012 per year; 95% CI, 1.0-1.025) and number of FNA passes (1 vs. 4+; OR, 6.07; 95% CI, 2.27-16.21). The complication rate was 1.1% related to perilesional hematomas and vaso-vagal episodes. Conclusion Thyroid FNA is a safe and reliable procedure for cytological assessment of thyroid nodules. Deeper nodules and older patients are more likely to have non-diagnostic samples.