Objective To analyze the ultrasonic features of papillary thyroid microcarcinoma (PTMC) and the related factors of false negative and false positive extrathyroid invasion. Method 70 patients with suspected PTMC admitted to Daping Hospital of the Army Medical University from October 2019 to September 2021 were selected for ultrasound examination. Based on the postoperative pathological diagnosis, the ultrasonic characteristics of PTMC were observed, the value of extrathyroid invasion in PTMC was evaluated, and the influencing factors of false negative and false positive were analyzed. Result The ultrasonic features of PTMC were as follows: lesion diameter ≤ 1cm, irregular shape, unclear boundary, aspect ratio ≥ 1, blood flow grade Ⅰ ～ Ⅱ , cystic
consolidation, hypoechoic solid part, silent halo and calcification. In 70 cases, 69 cases of PTMC were detected by pathological diagnosis. The sensitivity, specificity and accuracy of ultrasonic diagnosis of PTMC were 97.1%, 100.0% and 97.1% respectively. There was no significant difference compared with pathological diagnosis (P＞ 0.05). Among 69 cases of PTMC, 29 cases of extrathyroid invasion were detected by pathological diagnosis. The sensitivity, specificity and accuracy of ultrasonic diagnosis were 58.6%, 75.0% and 73.9%, respectively, with significant difference compared with pathological diagnosis (P ＜ 0.05); the true negative and false positive cases of PTMC without extrathyroid invasion had significant difference in lesion diameter, and the proportion of false positive diameter above 5mm was higher (P ＜ 0.05); the true positive and false negative cases of PTMC extrathyroid invasion had significant difference in lesion diameter, and the proportion of false negative diameter
≤ 5mm was higher (P ＜ 0.05); The proportion of false negative lesions with aspect ratio ≥ 1 was higher (P＜ 0.05); The proportion of false negative adjacent trachea was lower (P ＜ 0.05); The proportion of false negative bilateral lobe lesions was lower (P ＜ 0.05). Conclusion Ultrasound has high sensitivity, specificity and accuracy in the diagnosis of PTMC. In the diagnosis of extrathyroid invasion of PTMC, the main cause of false positive was the diameter of lesion > 5mm, the diameter of lesion ≤ 5mm, the aspect ratio of lesion ≥ 1, adjacent trachea and bilateral lobe lesions. In the process of ultrasonic diagnosis of PTMC, in-depth analysis of the above factors can reduce the missed diagnosis and misdiagnosis rate of extrathyroid invasion, and provide a reliable basis for surgical treatment.
