Preoperative differentiation between noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) and non-NIFTP.

BACKGROUND: A recent concept was proposed that the noninvasive encapsulated follicular variant of papillary thyroid carcinoma reclassified as "noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)" is benign. Our aim was to identify the differences between NIFTP and non-NIFTP preoperatively.

METHODS: This retrospective study included a total of 208 patients with 208 follicular variant of papillary thyroid carcinomas (FVPTC) that were surgically confirmed at three university hospitals from 2008 to 2014. Clinical factors, the biopsy techniques and ultrasonography (US) imaging characteristics were compared between the NIFTP and non-NIFTP groups.

RESULTS: A total of 34 NIFTP (16·3%) and 174 non-NIFTP (83·7%) were observed. For NIFTPs, the need for surgery was indicated by ultrasonography-guided fine needle aspiration (US-FNA) in 54·3% and by ultrasonography-guided core needle biopsy (US-CNB) in 100% (P = 0·008). For non-NIFTP, no significant difference was noted in the rates of surgical indication between US-FNA and US-CNB (62·6% vs 78·9%, P = 0·054). The most common biopsy diagnosis of NIFTP was Bethesda category V (28·6%) in the US-FNA group and category IV (45·5%) in the US-CNB group. US diagnosis of NIFTP had a significantly lower rate of the high suspicion of malignancy than that of non-NIFTP (14·7% vs 37·9%, P = 0·024). Central nodal metastasis was found in only one case (2·9%) of NIFTP patients, but none had distance metastasis or recurrence.

CONCLUSION: Noninvasive follicular thyroid neoplasm with papillary-like nuclear features lacks malignant US features and is better triaged using US-CNB than using US-FNA to facilitate the surgical management. US evaluation is pivotal in determining the next step of FVPTC management.