Fine-needle aspiration of the thyroid.
BACKGROUND: Although fine-needle aspiration (FNA) of the thyroid is the key preoperative investigation of thyroid lesions, there are overlaps in the criteria for diagnosis of certain lesions, particularly important among which are those for follicular neoplasms. A proposal for a 5-category working system for thyroid FNA diagnosis is presented, devised using clearly defined diagnostic guidelines with a prospective 2-year evaluation in 1 center. METHODS: The results of FNA of 156 patients with nodular thyroid lesions are presented. All patients were observed over a 2-year period in a multidisciplinary thyroid clinic. In some cases, the aspirates were repeated before excision of the lesion. The results of the FNA are classified by worst category for each patient, according to a 5-category scheme: THY1: inadequate; THY2: benign; THY3: indeterminate; THY4: suspicious lesion; THY5: malignant. RESULTS: Seventy-five of the 156 patients (48.1%) proceeded to excision, of these 50 (67%) showed multinodular goiter or adenomatoid nodule within a goiter, 7 (9.3%) showed evidence of Hashimoto thyroiditis or lymphocytic thyroiditis alone, 1 (1.3%) showed evidence of Reidel thyroiditis, and 1 (1.3%) showed evidence of a parathyroid cyst. Eight patients (11%) showed evidence of follicular adenoma, and 5 patients (6.6%) showed papillary carcinoma; 1 (1.3%) showed follicular carcinoma, and 2 (2.7%) showed lymphoproliferative disease. There was a significant difference in the number of benign as compared with neoplastic thyroid lesions excised in the indeterminate (THY3) (2 of 13 [15%]) as compared with the suspicious categories (THY4) (10 of 24 [42%]), (P = 0.05). Although no false-negative FNAs were identified in this series, there was 1 false-positive (THY5) FNA. CONCLUSIONS: The use of an indeterminate (THY3) category is helpful because it improves the diagnostic efficacy of thyroid FNA. The indeterminate (THY3) category is clinically useful and may markedly reduce or eliminate false-negative FNA in many patients with thyroid nodules. Cancer (Cancer Cytopathol)