Table 1 Diagnostic Categories of Thyroid Core Needle Biopsy Proposed by The Korean Endocrine Pathology Thyroid Core Needle Biopsy Study Group

I. Nondiagnostic or unsatisfactory

• Normal thyroid tissue only

• Extrathyroid tissue only (e.g., skeletal muscle, mature adipose tissue)

• A virtually acellular specimen

• Acellular/paucicellular fibrotic nodule

• Blood clot only

• Other

II. Benign lesion

• Benign follicular nodule or consistent with a benign follicular nodule

• Hashimoto’s thyroiditis

• Granulomatous (subacute) thyroiditis

• Nonthyroidal lesion (e.g., parathyroid lesions, benign neurogenic tumors, benign lymph node)

• Other

III. Indeterminate lesion

IIIA. Indeterminate follicular lesion with nuclear atypia

• Follicular proliferative lesions with focal nuclear atypia

• Follicular proliferative lesions with equivocal or questionable nuclear atypia

• Atypical follicular cells embedded in a fibrotic stroma

IIIB. Indeterminate follicular lesion with architectural atypia

• Microfollicular proliferative lesion lacking a fibrous capsule or the adjacent nonlesional tissue in the specimen

• Solid or trabecular follicular lesion lacking a fibrous capsule or the adjacent nonlesional tissue in the specimen

• Macrofollicular proliferative lesion with a fibrous capsule

• Hürthle cell proliferative lesion lacking a fibrous capsule or the adjacent nonlesional tissue in the specimen

IIIC. Other indeterminate lesions

IV. Follicular neoplasm or suspicious for a follicular neoplasm

• Microfollicular proliferative lesion with a fibrous capsule

• Mixed microfollicular and normofollicular proliferative lesion with a fibrous capsule

• Solid/trabecular follicular proliferative lesion with a fibrous capsule

• Hürthle cell proliferative lesion with a fibrous capsule

• Follicular neoplasm with focal nuclear atypia

V. Suspicious for malignancy

• Suspicious for papillary carcinoma, medullary carcinoma, poorly differentiated carcinoma, metastatic carcinoma, lymphoma, etc.

VI. Malignant

• Papillary thyroid carcinoma, poorly differentiated carcinoma, undifferentiated (anaplastic carcinoma), medullary thyroid carcinoma, lymphoma, metastatic carcinoma, etc.