Cytologic Features of Follicular sAdenoma and Follicular Carcinoma of the Thyroid: A Study on the Likelihood of Cytologic Diagnosis by Fine Needle Aspiration Cytology

【Fine-needle aspiration cytology (FNAC) cannot differentiate follicular adenoma from follicular carcinoma since this distinction can only be based on the presence of capsular or vascular invasion, and this can￢not be detected on a cytologic smear. The goal of this study was to define the diagnostic cytologic findings of follicular neoplasm and the possibility of diagnosing follicular neoplasm by performing FNAC. The cases of histologically diagnosed follicular adenoma and follicular carcinoma on the thyroidectomy specimens were retrieved. Among them, the cases with preoperative FNAC that was done within 3 months of the operation were finally selected. Then we reviewed the FNAC and histologic slides of 19 cases: 9 follicular adenomas and 10 follicular carcinomas. Our results suggest that for cases of follicular neoplasm, the aspirates show high or abundant cellularity, frequent follicle formation and occasional cellular atypism of the follicular cells. However, the atypism is more pronounced and more frequently noticed in the cases of follicular carcinoma, which reveals more higher anisocytosis (7/10, 70%), nuclear pleomorphism (9/10, 90%), coarse clumping of chromatin (8/10, 80%) and cellular overlapping (8/10, 80%).】