Discrepancy between Preoperative Fine Needle Aspiration Cytology and Postoperative Histologic Diagnosis in Follicular Tumors of the Thyroid

Han, Sehwan; Lee, Myung Soo; Kim, Hong Joo; Kim, Young Duck; Kim, Hong Yong

Abstract

Histologically, the diagnosis of a pure follicular carcinoma of the thyroid is difficult. It is generally not possible to distinguish between a follicular adenoma and a follicular carcinoma without examining the removed specimen, although follicular neoplasms can be identified on cytologic specimens from fine needle aspiration cytology(FNAC). The purpose of the present study is to evaluate the diagnostic accuracy of preoperative FNAC. A total of 42 cases were diagnosed as follicular neoplasms by FNAC while 50 cases were confirmed as follicular tumors after histologic examinations of removed specimens; follicular carcinoma 34, follicular adenoma 10, Hurthle cell carcinoma 3, Hurthle cell adenoma 3. When we compared the postoperative histologic diagnosis of the 42 cases which had been thought to be follicular neoplasms based on FNAC, 31(74.6%) had true follicular tumor; 20 carcinomas, 5 adenomas, and 6 Hurthle cell tumors. The other 11 cases were comprised of 6 follicular variant papillary carcinomas, 4 adenomatous goiters, and 1 instance of Hashimoto's disease. The 34 preoperative diagnoses of follicular carcinomas which were confirmed postoperatively were as follows; follicular neoplasm 20, adenoma 6, papillary carcinoma 5, and Hurthle cell tumor 3. Diagnosis of 10 follicular adenoma was made preoperatively as follicular neoplasm in 5 cases, adenomatous goiter in 3, and Hurthle cell tumor in 2 cases. It was impossible to distinguish a follicular carcinoma from a benign adenoma in 9 cases by using FNAC. Three patients with follicular carcinoma, who underwent a unilateral lobectomy because of inaccurate diagnosis, experienced recurrent disease, 2 with pulmonary metastasis and 1 with bone metastasis, with median follow-up period of 38 months(range: 6~71 months). There are no reliable diagnostic tools to dicriminate between follicular carcinoma and follicular adenoma preoperatively. In conclusion, the best way to establish a diagnosis and to predict prognosis is to surgically remove the tumor for a proper histopathologic examination.