Clinical meaning
Chest X-ray (CXR) interpretation requires a systematic approach to avoid missing pathology. The most commonly used mnemonic is ABCDEFGHI: Airway (trachea midline? deviated suggests tension pneumothorax, large effusion, or mass), Bones (fractures, lytic/blastic lesions, rib notching in coarctation of aorta), Cardiac (heart size — cardiothoracic ratio >0.5 on PA film = cardiomegaly; boot-shaped = tetralogy of Fallot; water-bottle = pericardial effusion), Diaphragm (right should be 1-2 cm higher than left due to liver; flattened = hyperinflation/COPD; free air under diaphragm = pneumoperitoneum from perforated viscus), Effusion/Edges (costophrenic angle blunting = pleural effusion ≥200 mL; check lung edges for pneumothorax — absent lung markings peripherally with visible pleural line), Fields (lung parenchyma — consolidation = white/opaque area representing fluid-filled alveoli: pneumonia, hemorrhage, edema; ground-glass = hazy opacity where vessels still visible: interstitial disease, early infection, ARDS; hyperinflation = >10 posterior ribs visible, flattened diaphragms: COPD/emphysema), Great vessels (widened mediastinum >8 cm = consider aortic dissection, lymphoma, or mass), Hilum (hilar lymphadenopathy = sarcoidosis, lymphoma, lung cancer, infections), Instrumentation (lines, tubes — ETT tip 2-4 cm above carina, central line tip at cavoatrial junction, NG tube tip below diaphragm in stomach). Key patterns: air bronchograms (air-filled bronchi visible within consolidated lung = alveolar filling process, most commonly lobar pneumonia), Kerley B lines (horizontal lines at lung periphery = pulmonary edema/lymphangitic carcinomatosis), silhouette sign (loss of normal cardiac or diaphragmatic border indicates adjacent consolidation in the same anatomical plane).