Application of the Bethesda system to "indeterminate" Category in Thyroid Fine Needle Aspiration : What is still being remained inconclusively?

초록

Background: The diagnostic category of "indeterminate" can confusion not only clinicians but also cytopathologists due to different criteria and ununified reporting system between institutions. In this study, we evaluated the usefulness of reclassifying "indeterminate" diagnoses in reporting thyroid aspiration cytology using Bethesda system, and then analyzed the causes of cases which were not clearly classified. Methods: We reviewed and reclassified cytologic specimens from 154 "indeterminate" cases of thyroid FNA that were histologically confirmed from June 2004 to Sept. 2009 in the Inha University Hospital of Korea. Results: The initial cytologic results were indeterminate in 363 of total 6508 cases (5.6%). 154 indeterminate cases underwent subsequent thyroidectomy ; 78 nodular hyperplasias, 5 Hashimoto's thyroiditis, 44 papillary carcinomas, 6 follicular adenomas, 5 Hurthle cell adenomas, 10 follicular carcinomas, 1 Hurthle cell carcinoma, 1 parathyroid adenoma, 1 hyalinizing trabecular tumor, and 1 poorly differentiated carcinoma. According to Bethesda system, indeterminate cases were reclassified as 5 insufficient for diagnosis (3.2%), 43 benign (27.9%), 80 atypical cells of undetermined significance(ACUS) (51.9%), 11 suspicious for a follicular neoplasm (7.1%), 4 suspicious for a Hurthle cell neoplasm (2.6%), 9 suspicious for malignancy ( 5.8%), and 2 malignancy (1.3%). All reclassified cases to benign and malignancy categories are correlated with histologic diagnoses. In the 80 ACUS, follow up surgical resection showed 33 malignacy (43.8%), including 33 papillary carcinomas, 2 follicular carcinomas, and 45 benign (56.2%) including 36 nodular hyperplasias, 3 Hashimoto's thyroiditis, 4 follicular adenomas, 1 Hurthle cell adenomas, and 1 hyalinizing trabecular tumor. Among 33 papillary carcinomas cytologically reclassified ACUS, 22 cases (67%) are microcarcinomas and 5 cases (15.1%) are follicular variant. As a result of analyzing of ACUS, specim