Needle aspiration cytology of thyroid cancer: Diagnostic accuracy and source of false negative

Between 1987 and 1991, fine-needle aspiration (FNA) cytology was performed in atotal of 112 cases of histologily confirmed thyroid cancer at the Center for Adult Diseases, Osaka, FNA cytology resulted in a positive diagnosis in 94 (83.9%) of these 112 cases.The diagnostic accuracy of palpation, ultrasonography and radiography in the same cases of thyroid cancer was 67.0%, 58.6% and 50.0%, respectively.Thus, FNA cytology was superior to other methods in diagnosing thyroid cancer.FNA cytology provided much higher accuracy, 87.1%, in diagnosing papillary carcinoma than ultrasonography and radiology. Suspicious and false negative cases of thyroid cancer were retrospectively analyzed.In papillary carcinoma, there appeared to be three sources of cytology errors.In four cases, identification of cancer cells was difficult because of a lack of characteristic cytological findings of papillary carcinoma.In six cases, the reason for suspicious and false negative diagnoses was related to histologic findings, such as tumor calcification, association with adenoma, and the presence of the follicular variant of papillary carcinoma.In three cases, inadequate smears were the source of cytodiagnostic errors, and in three cases of follicular carcinoma, cytological differentiation from follicular adenoma was very difficult because of cytomorphologic similarity.