A 2 month old was referred for ventricular septal defect closure. Echocardiography demonstrated malposed (crossed) pulmonary arteries and a large subarterial ventricular septal defect. Magnetic resonance imaging confirmed the anatomy. Transverse images (panels A, B, and C) show the crossing pulmonary arterial relationships in a superior to inferior progression. A portion of the large ventricular septal defect is seen in panel D. Panel E demonstrates the abnormal “stacking” of the left pulmonary artery superior to the right in the frontal plane. (LPA, left pulmonary artery; MPA, main pulmonary artery; RPA, right pulmonary artery; Ao, aorta; SVC, superior vena cava; RV, right ventricle; LV, left ventricle; LA, left atrium; RA, right atrium.)

Given the association of this uncommon malformation with deletion of chromosome region 22q11, a fluorescent in situ hybridisation (FISH) assay was performed. This was positive for haplo-insufficiency in the region. The infant underwent uneventful surgical correction.