Fine-needle aspiration of thyroid nodules: A study of 4703 patients with histologic and clinical correlations

BACKGROUND: The Papanicolaou Society of Cytopathology recently proposed 6 diagnostic categories for the classification of thyroid fine-needle aspiration (FNA) cytology. Using these categories, the experience with FNA from 2 institutions was studied with emphasis on cytologic-histologic correlation, source of errors, and clinical management. METHODS: Patient cytology data were retrieved by a retrospective search of thyroid FNA in the institutional databases. Cytologic diagnoses were classified as unsatisfactory, benign, atypical cellular lesion (ACL), follicular neoplasm (FN), suspicious for malignancy, and positive for malignancy. Samples with a histologic discrepancy were re-evaluated, and clinical follow-up information was recorded. RESULTS: Of 4703 FNA samples, 10.4% were classified as unsatisfactory, 64.6% were classified as benign, 3.2% were classified as ACL, 11.6% were classified as FN, 2.6% were classified as suspicious, and 7.6% were classified as malignant. Five hundred twelve patients had at least 1 repeat FNA, mainly for results in the unsatisfactory and ACL categories. One thousand fifty-two patients had surgical follow-up, including 14.9% of patients with unsatisfactory FNA results, 9.8% of patients with benign results, 40.6% of patients with ACL results, 63.1% of patients with FN results, 86.1% of patients with suspicious results, and 79.3% of patients with malignant results. The rates for histologically confirmed malignancy in these categories were 10.9%, 7.3%, 13.5%, 32.2%, 64.7%, and 98.6%, respectively. The cytologic-histologic diagnostic discrepancy rate was 15.3%. Sources of errors included diagnoses on inadequate specimens, sample errors, and overlapping cytologic features between hyperplastic nodules and follicular adenoma. The sensitivity and specificity of thyroid FNA for the diagnosis of malignancy were 94% and 98.5%, respectively. CONCLUSIONS: The current results indicated that FNA provides an accurate diagnosis of thyroid malignancy. The 6 diagnostic categories were beneficial for triaging patients for either clinical follow-up or surgical management.