Malignancy Risk and Diagnostic Accuracy of Fine-Needle Aspiration in Thyroid Nodules ≥4 cm: A Retrospective Analysis of Incidental Cancer.

IntroductionThe incidence of thyroid nodules measuring ≥4 centimeters (cm) has increased over the last decade and is particularly concerning for malignancy. However, the malignancy risk and diagnostic accuracy of fine-needle aspiration biopsy (FNAB) in nodules ≥4 cm remain debated. This study aims to determine the malignancy rate in nodules ≥4 cm and evaluate the diagnostic accuracy of FNAB.MethodsWe retrospectively analyzed patients who underwent partial or total thyroidectomy from January 2015 to December 2024 at a large tertiary care center. Data collected included patient demographics, thyroid nodule size, and final surgical pathology to determine the malignancy rate. Patients with nodules ≥4 cm were identified, and those who underwent FNAB were analyzed for diagnostic concordance between cytology and surgical pathology.ResultsAmong 1049 patients who underwent thyroidectomy, 167 (16%) had nodules ≥4 cm. Of these, 95 (57%) underwent preoperative FNAB and formed the analytic cohort. In this group, 14 patients (14.7%) had malignant final pathology, and 5 of these malignancies (35.7%) were incidentally discovered. Three of the incidental malignancies were papillary thyroid microcarcinomas (<1 cm) and were excluded from diagnostic performance analysis. Fine-needle aspiration biopsy demonstrated a sensitivity of 54.1%, specificity of 91.4%, false-negative rate of 20.99%, and positive predictive value of 81.3%. Concordance between FNAB and final pathology was observed in 79% of benign and 86% of malignant cases.ConclusionFine-needle aspiration biopsy demonstrates limited sensitivity in nodules ≥4 cm, with a 21% false-negative rate and potential for missed incidental malignancies. Based on this, surgical resection should be considered for thyroid nodules ≥4 cm.