Résumé : Purpose: To prospectively assess changes in lung volume in fetuses with isolated severe congenital diaphragmatic hernia (CDH) after fetoscopic endoluminal tracheal occlusion (FETO) compared with those in fetuses with CDH of variable severity who were expectantly managed. Materials and Methods: Informed consent was obtained for this ethics committee-approved study. Forty fetuses with severe CDH (lung-to-head ratio < 1 and intrathoracic liver) who underwent FETO and 18 fetuses with CDH of variable severity who were expectantly managed were longitudinally followed up by using magnetic resonance (MR) imaging volume measurements. Fetuses born prior to 32 weeks were excluded from the study. For those undergoing FETO, lung volume responsiveness was defined as the proportionate increase in observed-to-expected (O/E) ratio of total fetal lung volume (TFLV) at 2-5 weeks after FETO compared with the pre-FETO value. Changes in lung volume were compared by using the Mann-Whitney U test. Regression analysis was used to investigate the effect of pre-FETO O/E ratio of TFLV, gestational age at FETO and at delivery, lung volume responsiveness, occlusion period, side of CDH, and balloon removal prior to delivery on survival. Correlation between post-FETO lung volume responsiveness and gestational age at FETO was performed by using linear regression analysis. Results: A total of 260 MR imaging examinations were performed. For expectantly managed fetuses, O/E ratio of TFLV remained unchanged during gestation, whereas it significantly increased after FETO. Regression analysis demonstrated that pre-FETO O/E ratio of TFLV and lung volume responsiveness at 3.3 weeks after FETO provided significant independent prediction of postnatal survival. There was a significant negative association between lung volume responsiveness and gestational age at FETO. Conclusion: In fetuses with CDH, pre-FETO O/E ratio of TFLV and lung volume at 3.3 weeks after FETO provide independent prediction of postnatal survival. © RSNA, 2009.