Analysis of the Malignancy Rate for Thyroid Nodules based on the Use of a Fine Needle Aspiration Biopsy and Ultrasonography

Choi, Ju Wan; Park, Ji Won; Jeong, Han Young; Kim, Hye Jung; Kim, Gab Chul; Kim, Yong Sun; Park, Ji Young; Lee, Hui Joong

Abstract

PURPOSE: This study was designed to analyze the malignancy rate for thyroid nodules determined after a fine needle aspiration biopsy (FNAB) and ultrasonography (US) and to propose follow-up FNAB indications.
MATERIALS AND METHODS
A total of 287 patients (265 female, 22 male) who underwent repeated US-guided FNABs were included in the cohort study. The results of the FNABs were classified as inadequate, benign, indeterminate, suspicious for a malignancy and a malignancy. The US findings were assigned five grades according to the possibility of a malignancy present. The frequency of a malignant nodule was evaluated by the use of the Kaplan-Meier method and Cox proportional risk model.
RESULTS
The malignancy rates of inadequate, benign, and indeterminate nodules were 12.8%, 8.2% and 37.5%, respectively, for the FNAB findings. The rates of grades 3, 4 and 5 were 38.6%, 50.0% and 53.8%, respectively, for the US findings. Inadequate and indeterminate nodules as determined by an FNAB and grades 3, 4 and 5 assigned after US showed a higher malignancy rate than other nodules and would be regarded as high risk lesions. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 93.3%, 38.4%, 22.0%, 96.9% and 47.0%, respectively, if the nodule was considered a high-risk lesion, based on the FNAB or US findings.
CONCLUSION
Thyroid nodules should be evaluated based on an FNAB and US findings. If a thyroid nodule is classified as a high-risk lesion, a follow-up study is needed due to the high malignancy rate.