Figure 6d. (a) Anteroposterior view of necropsy specimen shows tracheal indentation (arrow) by innominate artery. The infant died of unrelated causes. (Photograph courtesy of W. Blanc, MD, Babies & Children’s Hospital of New York.) (b) Sagittal (left) and coronal (right) T1-weighted MR images (750/30). Left: The innominate artery (a) is anterior to and indenting the trachea (t). The vein (v) and thymus (th) are noted. Note the cervical extension of the thymus. Right: The innominate artery (arrows) passes in front and to the right of the trachea (t). (Images courtesy of G. Mandell, MD, DuPont Institute, Wilmington, Del.) (c) Tracheomalacia, or innominate artery syndrome. Histologic section of the midthoracic esophagus (E) and trachea (T) obtained at autopsy shows the tracheal cartilage is reduced in length and the membranous trachea is increased. The overall tracheal lumen is flattened. (Hematoxylin-eosin stain; original magnification, x30.) (Photograph of specimen courtesy of J. L. Emery, MD, Sheffield, England.) (d) Electron-beam CT images of tracheomalacia, or innominate artery syndrome. The same image level is noted to change the tracheal caliber from narrowed to normal during the respiratory cycle. The trachea is outlined in white. A = innominate artery. (Images courtesy of Wilbur Smith, MD, University of Iowa Hospitals & Clinics, Iowa City, Iowa.)