Fine-needle aspiration of thyroid: an institutional experience

In this report we describe our institutional experience with fine-needle aspiration (FNA) of the thyroid. Six hundred sixty-two FNAs were performed in 616 patients in a 3 1/2 year period. The cytological diagnoses were categorized as: negative for malignancy, 455 (69%); indeterminate, 30 (4%); neoplasm/malignant, 105 (16%), and nondiagnostic, 72 (11%) including 29 cases from outside institutions. Surgical follow-up was available in 140 (21%) cases, 95 of which had preceding cytological diagnoses of positive or indeterminate for neoplasm/malignancy. For those cases with definite benign or neoplastic/malignant cytodiagnosis, a sensitivity of 92% and specificity of 84% was achieved. The cumulative false-positive and false-negative rates for these categories were 16% and 7.5%, respectively. On comparing discrepant diagnosis between cytological and histological specimens, two major factors were identified as causes for diagnostic misinterpretations: overlapping cytological features among follicular-derived lesions and inadequate/suboptimal specimens. The cytological features of follicular variant of papillary carcinoma were found to overlap those of hyperplastic/adenomatous nodules and follicular neoplasms due to the presence of abundant thin colloid, monolayer sheets of follicular cells and subtle nuclear features of papillary carcinoma. We suggest that awareness of variable cytological features in follicular lesions (especially in follicular variant of papillary carcinoma), following strict criteria of specimen adequacy in thyroid FNA, and clinicopathological correlation can markedly reduce false-negative results.