Purpose or Case Report: Congenital high airway obstruction syndrome (CHAOS) is a rare life-threatening disease and prenatal diagnosis is essential. Some characteristic features seen on fetal MRI are well-known: primary lesion (upper airway obstruction) and secondary changes (dilated trachea, flattened/inverted diaphragm, enlarged and hyperintense lung). It is also reported that these secondary changes may be reduced if tracheoesophageal fistula (TEF) is present. The aim of this study is to evaluate the accuracy of fetal MRI in the prenatal diagnosis of CHAOS by comparing results with those of normal fetuses.
Methods & Materials: The MRI images from eight fetuses with CHAOS (29±6 weeks’ gestation [mean±SD]) and 37 fetuses with no thorax abnormalities (32±2 weeks) were assessed retrospectively. The fetuses with CHAOS were selected from among those who were diagnosed at our institution from 2006 to 2018 (four CHAOS fetuses with TEF were also included), and the normal fetuses were selected from consecutive fetal MRI performed in 2017 and 2018. Identification of the upper airway was evaluated in both groups (false negative rate [FNR] in the CHAOS group and false positive rate [FPR] in the control group). Measurement of tracheal diameter (TD), craniocaudal/antero-posterior ratio in the right diaphragm (CC/APR), cardiothoracic ratio (CTR), and lung-to-liver signal intensity ratio (LLSIR) were also carried out in both groups. For comparison between the CHAOS group and the control group, a t-test was used. Also, CHAOS fetuses with TEF were evaluated in the same way as described above.
Results: Upper airway obstruction could be detected in all fetuses with CHAOS (FNR=0%), while the upper airway could not be clearly identified in five fetuses in the normal group (FPR=13.5%). There was no statistical difference in TD (3.6±1.0 mm, 3.2 mm±0.5 mm, p=0.13) and LLSIR (2.64±0.68, 2.54±0.66, p=0.35) between the CHAOS group and the control group. However, CC/APR (4.4±14.1%) and CTR (45.9±7.2%) in the CHAOS group were significantly lower than those of the control group (23.3±4.5%, 57.1±3.8%, [p<0.05]). Also, the same statistical results were obtained for the CHAOS fetuses with TEF (TD [3.2±1.0 mm, p=0.48], CC/APR [14.5±7.4%, p<0.05], CTR [50.5±4.0%, p<0.05], and LLSIR [2.74±0.39, p=0.20]) as well as in all CHAOS patients.
Conclusions: CC/APR and CTR may reflect distension of the lungs and are more reliable predictors than TD and LLSIR for prenatal diagnosis of CHAOS, even where airway obstruction is incomplete (CHAOS accompanied by TEF).