The Role of Preoperative Fine Needle Aspiration Cytology (FNAC) in Differential Diagnosis of Thyroid Nodules

ABSTRACT

BACKGROUND: Fine Needle Aspiration Cytology (FNAC) is widely accepted as the most accurate procedure to differentiate malignant from benign thyroid nodules. It is a simple, safe, and inexpensive procedure, and the accuracy of FNAC is relatively high; however, its success usually depends upon the skill in using the aspiration technique and the experience and skill of the cytologist. The authors confirmed the diagnostic value of preoperative FNAC in differential diagnosis of thyroid nodules treated by the surgical resection. METHODS: Three hundred fifty specimens were taken in the Department of Surgery, Inje University College of Medicine, from July 1990 to June 1996. Fifty-one males and 299 females with ages ranging from 11 to 73 years were enrolled. The cytology of FNAC was compared to the final histologic diagnosis. RESULTS: The number of inadequate smears (or sampling error) was 15.7%. Preoperative cytologic diagnoses was consisted of 198 cases of benign disease (92 cases of nodular goiters, 96 cases of follicular lesion types III, and 10 cases of thyroiditis), 12 cases of highly suspicious malignant lesions (follicular lesions type II), and 85 cases of malignant disease (71 cases of papillary carcinomas and 14 cases of follicular lesions type I). Histologic diagnoses consisted of nodular goiters in 116 cases, adenomas in 66 cases, thyroiditis in 9 cases, papillary carcinomas in 84 cases, and follicular carcinomas in 20 cases. These results has an 84.6% sensitivity, a 95.2% specificity, a 15.3% false negative rate, and a 4.7% false positive rate. In the fifty-five cases of inadequate sampling, 13 cases (23.6%) were malignant lesions histologically. In the 16 cases proven as false negative, nine cases were papillary carcinomas, and 7 cases were follicular carcinomas histologically. Thirteen cases (16.1% of 27 cases of cystic lesions) of cystic nodules revealed malignant neoplasms histologically. CONCLUSION: FNAC is a single, useful diagnostic procedure for the initial screening for malignancy in thyroid nodules. Performing repeated aspiration in cystic nodules and clinically suspicious cases could reduce inadeguate sampling and the false negative rate.