Characterization of the Hyperintense Bronchus Sign as a Fetal MRI Marker of Airway Obstruction

Background: Fetal MRIbased differential diagnosis of congenital lung malformations is difficult because of the paucity of well-described imaging markers. Purpose: To characterize the hyperintense bronchus sign (HBS) in in vivo fetal MRI of congenital lung malformation cases. Materials and Methods: In this retrospective two-center study, fetal MRI scans obtained in fetuses with congenital lung malformations at US (January 2002 to September 2018) were reviewed for the HBS, a tubular or branching hyperintense structure within a lung lesion on T2-weighted images. The frequency of the HBS and respective gestational ages in weeks and days were analyzed. Areas under the curve (AUCs), 95% CIs, and P values of the HBS regarding airway obstruction, as found in histopathologic and postnatal CT findings as the reference standards, were calculated for different gestational ages. Results: A total of 177 fetuses with congenital lung malformations (95 male fetuses) and 248 fetal MRI scans obtained at a median gestational age of 25.6 weeks (interquartile range, 8.9 weeks) were included. The HBS was found in 79% (53 of 67) of fetuses with bronchial atresia, 71% (39 of 55) with bronchopulmonary sequestration (BPS), 43% (three of seven) with hybrid lesion, 15% (six of 40) with congenital cystic adenomatoid malformation, and 13% (one of eight) with bronchogenic cyst at a median gestational age of 24.9 weeks (interquartile range, 9.7 weeks). HBS on MRI scans at any gestational age had an AUC of 0.76 (95% CI: 0.70, 0.83; P = .04) for the presence of isolated or BPS-associated airway obstruction at histopathologic analysis and postnatal CT. The AUC of HBS on fetal MRI scans obtained until gestational age of 26 weeks (AUC, 0.83; 95% CI: 0.75, 0.91; P < .001) was significantly higher (P = .045) than that for fetal MRI scans obtained after gestational age 26 weeks (AUC, 0.69; 95% CI: 0.57, 0.80; P = .004). Conclusion: The hyperintense bronchus sign is a frequently detectable feature at fetal MRI and is associated with airway obstruction particularly before gestational age 26 weeks. (C) RSNA, 2021

Automated summary

The hyperintense bronchus sign (HBS) in fetal MRI is frequently associated with airway obstruction, particularly before gestational age 26 weeks. It can be detected in various congenital lung malformations and has a higher diagnostic accuracy in fetal MRI scans obtained until 26 weeks of gestational age compared to those obtained after 26 weeks.