Follicular variant of papillary thyroid carcinoma: comparison of ultrasound-guided core needle biopsy and ultrasound-guided fine needle aspiration in a multicentre study

Objective: Pre-operative diagnosis of the follicular variant of papillary thyroid carcinoma (FVPTC) by ultrasound-guided fine needle aspiration (US-FNA) remains a challenge. The goal of this study was to investigate whether ultrasound-guided core needle biopsy (US-CNB) is superior to US-FNA in refining the surgical indications for the treatment of FVPTC. Design: This retrospective study enrolled 212 patients with 218 FVPTCs who were surgically confirmed at three university hospitals from January 2008 through December 2014. All patients underwent both or either US-FNA or US-CNB. FNA and CNB results were divided into identified surgical candidates or not based on the Bethesda system. Relevant clinical information and the rate of surgical candidates were compared between US-FNA and US-CNB groups. Results: Among 218 thyroid nodules, US-FNA was performed for 200 nodules and US-CNB for 51 nodules. Thirty-three nodules underwent both US-FNA and US-CNB. The rates of surgical candidates identified by US-FNA and US-CNB were 61·5% and 86·3%, respectively (P = 0·001). The rates of surgical candidates identified by repeat US-FNA and initial US-FNA with subsequent US-CNB were 53·9% and 78·8%, respectively (P = 0·042). A precise diagnosis of FVPTC was made in 1% of the patients in the US-FNA group and in 29·4% of the patients in the US-CNB group. The predominant US findings of FVPTCs included solid tumours (89·4%), wider-than-tall shape (82·6%), no calcifications (51·3%), hypoechogenicity (46·3%) and indeterminate diagnosis on US (50·5%). Conclusions: In patients with FVPTC, US-CNB is a superior indicator for surgery compared to US-FNA. If a FVPTC is suspected but is initially indeterminate at FNA cytology, subsequent US-CNB should be considered instead of repeat US-FNA.