Comparative accuracy of fine-needle aspiration cytology between larger and smaller size thyroid nodules

Thyroid nodules are frequently encountered in medical practice. Fine needle aspiration cytology (FNAC) is used to rule out malignant nodules, but few studies have questioned the accuracy of FNAC in larger thyroid nodules compared to smaller ones. We, therefore, aim to compare the diagnostic performance of FNAC based on nodule size and whether larger nodule size increases the possibility of obtaining indeterminate or non-diagnostic results. Adult patients with thyroid nodules who underwent thyroid biopsy and surgery from 2016 to 2022 were included in the study. We assessed the proportion of benign, malignant, indeterminate, and non-diagnostic FNAC in relation to the nodule size. We then divided cytology into true positive (malignant FNAC and histology), and true negative (benign FNAC and histology) and examined whether the proportion of true FNAC would be affected by different thyroid nodule cutoffs. The study used mean and frequency to describe continuous and categorical variables. t-test and Chi-square tests were used to compare statistics. Three hundred and forty-five patients were included in the study. The majority were female (86.7%) and older than 40 years. Half had a benign histology; the other 50% were malignant. The majority (49.3%) had indeterminate thyroid cytology. The proportion of indeterminate or non-diagnostic FNAC was the same (58%) in nodules ≥4 cm and <4 cm. The proportion of true FNAC was similar between different nodule size categories. It was 35% in ≥4 cm, and 34.3% in <4 cm nodules. The study found that the diagnostic performance of FNAC in thyroid nodules did not significantly differ based on nodule size, with similar rates of indeterminate or non-diagnostic results across different size categories. The proportion of true positive FNAC results also remained consistent regardless of nodule size.