Introduction: Although thyroid fine-needle aspiration biopsy (FNAB) is established to have a good overall sensitivity and specificity, various outcomes have been reported on its performance in large nodules. The aim of the study was to evaluate the diagnostic performance of FNAB and the effect of the nodule diameter on its diagnostic performance.
Materials and methods: The outcomes of a total of 7319 patients who underwent FNAB over the course of 5 years were analyzed retrospectively and 648 patients who had undergone post-FNAB thyroidectomy or lobectomy were included in the study. FNAB results were classified according to the Bethesda system. After evaluating the compatibility between cytology and pathology results, all-nodules and diameter-based (<4 cm and ≥4 cm) sensitivity, specificity, false positivity, false negativity, and accuracy rates of FNAB were calculated.
Results: Sensitivity of FNAB was 85.4% for all nodules, 88.3% for nodules <4 cm, and 75.8% for nodules >4 cm (P < 0.001). Specificity was 58.4% for all nodules, 49.3% for nodules <4 cm, and 75.1% for nodules >4cm (P < 0.001). While false positivity was 41.6% for all nodules, it was 50.7% for nodules smaller than 4 cm and was 24.9% for nodules larger than 4 cm (P < 0.001). False negativity was 14.6% for all nodules and was 11.7% for nodules smaller than 4 cm and 24.2% for nodules larger than 4 cm (P < 0.001). Finally, among the entire set of nodules, the accuracy was 64.4%, which was 59.2% in nodules smaller than 4 cm, and 75.2% in nodules larger than 4 cm (P < 0.001).
Conclusion: Despite a higher rate of false negativity, FNAB has higher specificity and accuracy in large nodules than those in the small nodules. Nodule diameter should not be used alone as a criterion to recommend thyroidectomy to the patient.
Keywords: Fine-needle aspiration biopsy; malignancy; nodule; thyroid.