OBJECTIVE To explore the diagnostic value of multi-slice spiral CT(MSCT)dynamic enhanced scan in lymph node metastasis of thyroid cancer,and to analyze the causes of missed diagnosis by MSCT dynamic enhanced scan.METHODS A total of 88 patients with thyroid cancer diagnosed by surgery and pathology admitted to the 924th Hospital of the Joint Logistic Support Force of the People's Liberation Army of China from March 2022 to July 2023 were selected.All patients underwent routine CT plain scan and MSCT dynamic enhanced scan.The results of the two scanning methods were compared with postoperative pathological examination as the gold standard.The influencing factors of missed diagnosis of MSCT were analyzed by multivariate Logistic analysis.Chi-square automatic interactive detection(CHAID)classification tree algorithm was used to construct the prediction model of missed diagnosis,and the benefit graph and index graph were used to evaluate the clinical application value of the model.RESULTS The missed diagnosis rates of lymph node metastasis in conventional CT scan and MSCT dynamic enhanced scan were 39.13%and 13.04%,respectively.The diagnostic sensitivity,specificity,accuracy and positive predictive value in MSCT group were 86.96%,87.69%,87.50%and 71.43%,which were significantly higher than those in conventional CT scan group.The MSCT group showed high consistency with the gold standard diagnosis(Kappa=0.726).The results of multi-factor analysis showed that irregular edge,blurred edge,calcification,involvement of envelope and cystic change were the risk factors of missed diagnosis.The results of classification tree model showed that calcification had the greatest influence on missed diagnosis among 5 factors,which were edge irregularity,edge blur,calcification,involvement of envelope and cystic degeneration.The results show that the model is effective in predicting missed diagnosis.CONCLUSION The accuracy and sensitivity of MSCT dynamic enhanced scan in the diagnosis of lymph node metastasis of thyroid cancer are high,and the diagnostic results can provide a reference for early diagnosis and further treatment,and have high application value.