[Management of fetal mediastinal shift: a practical approach]

The purpose of this article is to review the technique of fetal chest ultrasound screening evaluation, the diagnostic work-up in the presence of fetal mediastinal shift and which ultrasound imaging features to look for. The first step in evaluating the fetal thorax is to confirm situs. Then, a median sagittal line is drawn from a four-chamber view to assist in spatial orientation followed by echotexture analysis of the structures of the thorax in the presence of mediastinal shift. We propose a systematic approach based on the direction of the mediastinal shift and echogenicity of the compressing hemithorax. When the hemithorax contralateral to the mediastinal shift is enlarged, which is the most frequent situation, diaphragmatic hernia and macrocystic congenital cystic adenomatoid malformation are the most likely etiologies when the mass is heterogeneous. Microcystic congenital cystic adenomatoid malformation, sometimes associated with sequestration, is the most frequent etiology when the mass is homogeneous. When the hemithorax ipsilateral to the mediastinal shift is small, which is less frequent, and the contralateral hemithorax is homogeneously isoechoic, then a diagnosis of lung hypoplasia-agenesis-aplasia should be considered.