The role of core needle biopsy in the preoperative diagnosis of follicular neoplasm of the thyroid

Follicular neoplasm/suspicious for follicular neoplasm (FN/SFN) can often be challenging to diagnose using core needle biopsy (CNB) specimens. We have developed the histologic criteria for the CNB diagnosis of FN and validated the usefulness of CNB. We retrospectively reviewed 184 CNBs and 224 FNACs diagnosed with FN/SFN. CNBs were histologically classified into four subgroups, based on the histologic features of follicular proliferation, fibrous capsulation, and surrounding parenchyma. Among 184 CNBs, 103 (55.9%) had previous FNAC results of non-diagnostic or indeterminate. Overall malignancy rates in FNAC (48%) and CNB (46%) were nearly identical (p > 0.05), and the neoplasm rate was higher in CNB (88%) than FNAC (74%) (p = 0.007). There was no significant difference in the malignancy rates among the four histologic subgroups. Among the 40 nodules with simultaneous CNB and FNAC, only nine had the FNAC diagnosis of FN/SFN, and others were non-diagnostic, benign, or atypia of undetermined significance. Overall, CNB improved specimen adequacy and achieved better sensitivity of the FN/SFN diagnosis in thyroid nodules that were inconclusive by FNAC. In the preoperative diagnosis of FN/SFN, CNB has no advantage over FNAC in predicting the likelihood of malignancy, but helps to reduce the need for repeat biopsy.