Objective:To evaluate the differential diagnosis of papillary thyroid carcinoma (PTC) based on CT signs.Methods:Retrospective analysis was performed on 156 patients with PTC confirmed by surgery and pathology in the Imaging Department of Jinhua Hospital Affiliated to Zhejiang University College of Medicine from Jan. 2017 to Jan. 2022 as PTC group, and 132 patients with nodular goiter (NG) as NG group. There were 112 females and 45 males in the PTC group. The age was (49.32±3.25) years. There were 104 females and 52 males in NG group. The age was (50.12±3.27) years. Preoperative plain and contrast-enhanced CT scans were performed to analyze the features of the images, and univariate analysis was performed on the morphologic features, high tension, plain "bite cake sign" , enhanced "bite cake sign" , microcalcification, blurred/reduced scope after enhancement, nodule density, and asymmetric diffuse enlargement of thyroid gland. Statistically significant factors were included in the multivariate Logistic regression analysis, and the differential model of PTC was established according to the selected risk factors. The value of the model in the differential diagnosis of PTC was evaluated by ROC curve.Results:The percentages of irregular shape, no high tension, plain scan "bite cake sign" , enhanced "bite cake sign" , microcalcification, enhanced blur/reduced scope, uniform nodule density, completely slightly low tissue density, no cystic degeneration, and asymmetric thyroid diffuse enlargement in PTC group were higher than those in NG group ( χ2=161.014, 3.387, 95.885, 151.331, 60) . 200, 18.104, 105.260, 16.855, 89.064, 16.913, P<0.05) , suggesting that the above CT signs had important diagnostic value in differentiating PTC and NG. Among the single CT signs, plain scan "bite cake sign" had the highest sensitivity, specificity and accuracy. The sensitivity of PTC diagnosis combined with other signs gradually decreased, while the specificity gradually increased. At the same time, plain scan "bite cake sign" and microcalcification signs had high specificity in PTC identification, and the specificity of PTC identification reached 100.00% when any 4 or more signs were present. Multivariate Logistic regression analysis. The results showed that irregular morphology ( OR=15.831, 95% CI: 7.444-33.670) , high tension ( OR=0.162, 95% CI: 0.108-0.242) , plain scan "bite cake sign" ( OR=5.601, 95% CI: 2.691-11.659) , microcalcification ( OR=4.031, 95% CI: 2.062-7.880) , edge blur/range reduction after enhancement ( OR=4.761, 95% CI: 3.126-7.260) , uniform density of nodules ( OR=4.778, 95% CI: 3.299-6.290) and increased asymmetric diffusion ( OR=3.758, 95% CI: 1.911-7.391) were important signs for distinguishing NG from PTC ( P<0.05) . The above factors were incorporated into the Logistic regression equation to construct the model, and then the ROC curve was drawn. The results showed that the area under the curve of the model established based on CT signs was 0.94 (0.925-0.983) , and the sensitivity and specificity were 90.37% and 91.45%, respectively. Conclusions:In CT signs, irregular shape, high tension, "biting cake sign" on plain scan, microcalcification, blurred edge/scope reduction signs after enhancement, and uniform nodule density are important signs for differentiating papillary thyroid carcinoma from nodular goiter. The constructed model has good predictive value for identifying papillary thyroid carcinoma.