Which radiographic pattern best supports a diagnosis of pulmonary atresia in a cyanotic neonate?

• A. Normal heart size with prominent pulmonary vasculature
• B. Enlarged pulmonary arteries with increased vascular markings
• C. Increased cardiothoracic ratio with decreased pulmonary vasculature
• D. Low diaphragms with diffuse interstitial markings

Answer: (C)

Pulmonary atresia produces little or no blood flow to the lungs because the outflow tract from the right ventricle is blocked. That reduced pulmonary perfusion shows up on chest radiographs as diminished pulmonary vasculature. The heart may look enlarged because of right ventricular enlargement or pressure overload from the obstruction, so the cardiothoracic ratio can be increased. Put together, a cyanotic neonate with an enlarged cardiac silhouette and reduced lung vascular markings fits this lesion best. Other patterns—normal heart size with prominent vessels, or enlarged pulmonary arteries with increased markings, or diffuse interstitial markings with low diaphragms—point to different processes (higher flow states, pulmonary hypertension, edema or infection) and do not match the typical low-pulmonary-flow physiology of pulmonary atresia.