To investigate the sonographic and clinical features of follicular variant papillary thyroid carcinoma (FVPTC).

One hundred and twenty-seven FVPTC nodules that were confirmed by pathology at Ruijin Hospital, Shanghai Jiaotong University from January 2007 to October 2017 were retrospectively analyzed. The sonographic features assessed included maximum diameter, margin, orientation, composition, echogenicity, calcification, posterior attenuation, halo, and vascularization. The indexes were incorporated into the thyroid ultrasound imaging report and data system (TI-RADS), and the TI-RADS classification of FVPTC was then compared with that of classic PTC. At the same time, ultrasound-guided fine-needle aspiration biopsy (US-FNAB) and lymph node metastasis of FVPTC were analyzed. The t-test was used to compare the difference in size and the χ² test was used to compare the difference in lymph node metastasis and TI-RADS classification between FVPTC and classic PTC groups.

The mean size of FVPTC nodules was (23.47±12.75) mm, which was significantly larger than that of classic PTC [(10.84±6.10) mm; t=10.077, P＜0.001]. Most of FVPTCs had sonographic features of smooth margin, aspect ratio ≤1, being solid, hypoechoic echogenicity, no calcification, no posterior attenuation, no sound halo, and medium blood supply. TI-RADS classified showed that FVPTC and classic PTC were statistically different (χ²=28.891, P＜0.001), but between non-adenomas-like FVPTC and classical PTC there was no difference (χ²=3.988, P=0.125). The coincidence rate of US-FNAB with pathological diagnosis in FVPTC was 55.56% (15/27). The lymph node metastasis rate of FVPTC was lower than that of classic PTC (10.68% vs 29.92%; χ²=12.560, P=0.001).

FVPTCs have different sonograms and low lymph node metastasis rate. A deeper understanding of FVPTCs can effectively improve the accuracy of diagnosis.