Utility of a formatted pathologic reporting system in thyroid core needle biopsy: A validation study of 1998 consecutive cases

Objective: Thyroid core needle biopsy (CNB) is increasingly being used as a tool for evaluating thyroid nodules; thus, standardization of its diagnostic terminology is called for. We aimed to analyse the pathologic reporting system of thyroid CNB based on the recently proposed protocol by the Korean Endocrine Pathology Thyroid Core Needle Biopsy Study Group and evaluate its usefulness.

Design/methods: A total of 1998 consecutive cases of thyroid CNBs were reviewed and divided into six categories according to the protocol. Malignancy rate in each category and the diagnostic performance of thyroid CNB were calculated using 705 resected cases.

Results: Thyroid CNB yielded 132 nondiagnostic (6.6%), 791 benign (39.6%), 328 indeterminate (16.4%), 227 follicular neoplasm (11.4%), 69 suspicious for malignancy (3.5%) and 451 malignant lesions (22.6%). In resected specimens, all of the cases designated as suspicious for malignancy and malignant categories in CNB were proven to be true malignant lesions. Lesions diagnosed with follicular neoplasm in CNB were identified as malignant lesions in 57.0%. Malignancy rate was significantly higher in indeterminate lesions with nuclear atypia compared to those with architectural atypia (80.0% vs 28.2%). When CNB diagnoses of indeterminate lesions or higher categories were considered positive, the sensitivity and positive predictive value for final malignant diagnoses were 99.2% and 81.3%, respectively.

Conclusions: CNB is an accurate method of evaluating thyroid nodules and can serve as an alternative to fine needle aspiration when it is used and reported according to standardized diagnostic categories.