To analyze the high-frequency ultrasound (US) features of medullary thyroid carcinoma (MTC), and to compare the differences between MTC with the maximum diameter of ＞1.0 cm and ≤1.0 cm.

The clinical data, US images, and pathological results of 36 MTC patients who underwent high-frequency US examination and surgical resection at the First Medical Center of Chinese PLA General Hospital from January 2016 to December 2019 were analyzed retrospectively. The US features of MTC were summarized and a comparative study was performed between subgroups with the maximum diameter of ＞1.0 cm and ≤1.0 cm.

Forty-two MTC lesions with the maximum mean diameter of (2.6±1.5) cm (range, 0.4-5.4 cm) were enrolled in this study. MTC lesions were mainly distributed in the middle and upper poles of the thyroid (32, 76.2%); all were hypoechoic, 39 of them were mainly solid (39, 92.8%), and most of them had calcifications (25, 59.5%). Compared with lesions with the maximum diameter of ≤1.0 cm, the blood flow signal of lesions with the maximum diameter of ＞1.0 cm was more abundant (65.5% vs 7.7%, P=0.001); the rate of cervical lymph node metastasis in patients with lesions ＞1.0 cm was higher (79.3% vs 15.4%, P＜0.001), and US diagnosis accuracy in these cases was higher (93.1% vs 61.5%, P=0.0.037).

Most MTCs are located in the middle and upper poles of the thyroid, with solid component, hypo-echogenicity, and calcifications. Different sizes of MTC have different US features. Accurate differentiation of these US features is helpful for the early diagnosis and treatment of MTC.