The
Aortopulmonary window, seen on a normal lateral chest radiograph. Reference: “Aortopulmonary Window or Angle on the Chest Radiograph?”, in American Journal of Roentgenology, volume 182, issue 4, 2004, DOI:10.2214/ajr.182.4.1821085, ISSN 0361-803X, pages 1085–1086