The impact of using defined criteria for adequacy of fine needle aspiration cytology of the thyroid in routine practice.

The fine needle aspiration cytology (FNAC) of the thyroid is the predominant method of preoperative tissue diagnosis of thyroid lesions. The routine use of FNAC has reduced the rate of unnecessary surgery for thyroid nodules. However, there are overlaps in the existing criteria for defining adequacy in thyroid aspirates. In this study, we aimed to explore the reasons for high percentage of inadequate thyroid FNAC samples and to reevaluate those samples by applying clearly defined criteria suggested in the literature to reduce the proportion of inadequate aspirates. The results of 550 smears reported as inadequate FNAC samples are presented over a period of 15 years extending from 1986 to 2000 (18.8%). For the purpose of the study, only those patients with subsequent histological or cytological analysis were included (279). The original FNA samples were reviewed by two cytopathologists, unaware of the subsequent repeat cytology or histology results. Specific criteria for adequacy of specimens were used which include the presence of six or more groups of follicular cells, each having more than 10 discernable viable cells or 60 isolated viable follicular cells. Out of 279, 82 (29%) FNAC samples originally reported as inadequate met our criteria and were considered adequate on review. Of these 82 cases, subsequent surgical excision showed malignancy in 5 cases (6%), adenoma in 7 (9%), and benign hyperplasia and thyroiditis in 70 cases (85%). In addition, 16 (5%) cases were classified as cysts. The slide preparation error was noticed in 26 (14%) and the sampling error was observed in 160 (86%) cases. The use of well-defined criteria for adequacy is helpful because it improves the diagnostic efficiency of thyroid FNA and avoids unnecessary surgery for benign nonneoplastic thyroid lesions. However, since application of these criteria has also resulted in an increase in the false-negative diagnoses, they should be applied in the multidisciplinary context.