Abstract

Fine needle aspiration cytology(FNAC) has been used effectively as the initial modality in evaluating various thyroid lesions. We correlated cytologic and histopathologic features to investigate the diagnostic pitfalls of FNAC of the thyroid. A total of 1,593 FNACs of the thyroid were diagnosed at the Department of Pathology, Hanyang University Hospital, from January 1993 to December 1997. There were 963 cytologically benign cases(60.5%), 97 suspicious cases(6.1%), and 75 malignant cases(4.71%). The remaining 458 cases(28.8%) were unsatisfactory. Subsequent surgical resection was done in 192 cases. Seventy-two cases(37.5%) were cytologi cally diagnosed as benign, 45 cases(23.4%) suspicious, 56 cases(29.2%) malignant, and 19 cases(9.9%) unsatisfactory. Histopathologically, 101 cases were benign(11 thyroidites, 52 adenomatous hyperplasias, 34 follicular adenomas, and four Hurthle cell adenomas), and 91 cases malignant(72 papillary carcinomas, 16 follicular carcinomas, one medullary carcinoma, one anaplastic carcinoma, and one granular cell tumor). After excluding 19 unsatisfactory cases, 63 were misdiagnosed. They included 17 benign(three thyroidites and 14 adenomatous hyperplasias), 27 suspi cious(16 follicular adenomas, four Hurthle cell adenomas, and seven follicular carcinomas), and 19 malignant(16 papillary carcinoma, one medullary carcinoma, one anaplastic carcinoma, and one granular cell tumor) lesions. The accuracy rates in the benign, suspicious, and malignant categories were 54.9%, 49.8%, & 92.8%, respectively. The cytological pitfalls were as follows: (1) bloody background, (2) crowded follicular cell clusters indistinguishable between follicular neoplasia and adenomatous hyperplasia, (3) papillary structure, irregular nuclear membrane and pleomorphism mimicking those of papillary carcinoma, (4) indistinct eosinophilia in follicular epithelial cells, (5) unusual cellular components not commonly seen in FNACs of the thyroid.

• Keywords: FNAC;Thyroid;Cytopathologic analysis;Misdiagnoses