To investigate the value of 18 MHz high-frequency linear array ultrasound probe in the diagnosis of thyroid anterior capsular invasion, and compare it with the conventional high-frequency ultrasound probe.

Seventy-three nodules in 68 patients in Peking Union Medical College Hospital from December 2015 to March 2016 underwent conventional and 18 MHz high-frequency probes examination before operation and were compared with pathological results. The accuracy, sensitivity and specificity of the 18 MHz high-frequency linear array probe and the conventional high-frequency probe were determined. The consistency between the gold standard and the diagnosis by using two different frequency probes was measured using Kappa statistics. Additionally, diagnostic accuracy of different frequency probes was further evaluated according to the area under the ROC curve.

The diagnostic consistency test of the total sample of 73 nodules: ″capsular abutment″ as the diagnostic criterion, the diagnostic consistency of 18MHz high-frequency probe was good (Kappa=0.803, P<0.01). The specificity, positive predictive value and accuracy were superior to the conventional high-frequency probe (90.7% vs 69.8%, 87.1% vs 68.3%, 90.4% vs 79.5%). The area under the ROC curve was 0.903, higher than that of the conventional high-frequency probe (0.816), which demonstrated that the former had better diagnostic accuracy. If ″the disruption of the perithyroidal echogenic line″ as another diagnostic criterion, the diagnostic consistency of the 18 MHz and conventional high-frequency probe was general, the Kappa value were 0.677 and 0.518. The sensitivity, positive predictive value, negative predictive value and accuracy of conventional high-frequency probe were inferior to the 18 MHz high-frequency probe (53.3% vs 70.0%, 74.5% vs 82.0%, 88.9% vs 91.3%, 78.1% vs 84.9%).

The 18 MHz high frequency probe is a feasible tool for accurate prediction of the distance between tumor and thyroid anterior capsular and anterior capsular invasion, and it is helpful for the diagnosis of the preoperative staging and the prognosis of PTC.