[CT quantitative characteristics of peritumoral nodule in predicting invasiveness of thymoma]

Objective: To explore the value of CT quantitative features of peritumoral nodules in predicting invasiveness of thymoma. Methods: A retrospective study of 110 patients (65 males and 45 females, with a median age of 45 years) of thymoma with complete clinical, imaging and pathological data in Peking University Third Hospital from March 2013 to October 2018. Patients were divided into high risk (23 males and 15 females, with a median age of 52 years) and low risk groups (42 males and 30 females, with a median age of 42 years) according to the 2004 WHO criteria of thymoma. The major diameter, dual phase contrast CT values, ΔCT values and distance to main tumor of peritumoral nodule were analyzed. The predictive value of CT quantitative parameters were examined with Mann-Whitney U test and ROC curves. Results: Among 110 cases of thymoma, 28 cases had peritumoral nodules.The pathological classification of thymoma were type B1 (12 cases), type B2 (7 cases), type B3 (6 cases) and type C(3 cases). No peritumoral nodules were found in type A and AB.Sixteen patients were categorized into the high risk group whereas the other 12 patients were considered low risk. For high risk group, the major diameter, dual phase contrast CT values, ΔCT values and distance to main tumor of peritumoral nodule were (9.8±3.7) mm, (48±27)HU, (51±21)HU, (17±10)HU and (6.3±6.5)mm, respectively; and for low risk group, the major diameter, dual phase contrast CT values, ΔCT values and the distance to main tumor of peritumoral nodules were (5.5±1.6)mm, (55±18)HU,(52±19)HU, (14±10)HU and (3.9±2.2)mm, respectively. Compared with the low risk group, the major diameter was significantly higher in high risk group (P<0.05). In contrast, dual phase contrast CT values, ΔCT values and the distance to main tumor only changed slightly (all P>0.05). The ROC curve analysis indicated that, the cutoff of the major diameter of peritumoral nodule predicting tumor's high risk was 6.9 mm, and the corresponding AUC, sensitivity, and specificity was 0.862, 75.0% and 75.0%, respectively. Conclusion: The major diameter of peritumoral nodule can potentially predict the invasiveness to thymoma.