The effect of thyroid nodule size on diagnostic accuracy - a retrospective analysis of a medium-sized cohort

Summary: Size is an important parameter to consider in the clinical evaluation of thyroid nodules. Among other parameters, size determines the indication for fine-needle aspiration cytology (FNA). Literature data concerning the relationship between nodule size and FNA diagnostic accuracy is contradictory. We retrospectively studied cytological reports of a medium-sized cohort and analyzed the relationship between thyroid nodule size and the accuracy of the cytological diagnosis. Materials and Methods. We retrospectively analyzed the reports of 2634 FNA samples (representing 2569 patients who underwent thyroid FNA between 2012 and 2021). Of these, 106 patients were followed clinically or by repeat FNA, and 131 underwent thyroid removal surgery (partial or complete) with the available pathology reports. Cytological diagnoses were classified as true positive (TP), false positive (FP), true negative (TN), and false-negative (FN) based on cytohistological correlation. We analyzed the difference between thyroid nodule sizes in these groups using the Student's t-test method. Results. The cytohistological correlation identified 102 TP, 11 FP, 12 TN, and 4 FN diagnoses. A significant size difference was identified between the TP and FP groups (p=0.042, 16.4±1 mm vs. 23 ± 3.7 mm). Conclusion. Our results indicate that thyroid size alone does not influence global diagnostic accuracy. However, it also shows that larger thyroid nodules are more prone to false-positive type diagnostic error.