Quality and Adequacy First

Before interpreting, assess image quality: Rotation: spinous processes should be centered between clavicular heads. Adequate inspiration: should see ≥6 anterior ribs or ≥10 posterior ribs above the diaphragm; hyperinflation (>10 posterior ribs) suggests COPD or asthma. Exposure: vertebral bodies should be faintly visible through the cardiac shadow on a properly exposed PA film. If AP (portable): heart appears larger due to magnification and divergent beam — always note 'PA vs AP' before commenting on cardiac size. Technical factors: patient positioning, motion artifact.

A — Airway

Trachea: should be midline at the level of the clavicles. Tracheal deviation toward lesion = volume loss (atelectasis, lung collapse). Tracheal deviation away from lesion = mass effect (tension pneumothorax, large pleural effusion, large mass). Carina: normally <70° angle (Paget's disease of bone, right heart enlargement, or large LA enlargement from mitral stenosis widens the carina >70° — classic radiograph finding). Endotracheal tube (if present): tip should be 3-4 cm above carina (at T2-T4 level).

B — Breathing (Lung Fields)

Consolidation: airspace disease — fluffy, dense, homogeneous opacification; air bronchograms present (air-filled bronchi visible within dense consolidation); lobar or segmental distribution; causes = pneumonia (#1), pulmonary edema (bilateral), hemorrhage, aspiration. Atelectasis: plate-like (subsegmental — most common post-op), lobar, or complete lung collapse. Lobar collapse patterns: RML collapse = obliteration of right heart border (silhouette sign); LLL collapse = obscures left heart border (lingular); RLL collapse = obscures right hemidiaphragm. Interstitial pattern: reticular or reticulonodular pattern; increased interstitial markings; causes = pulmonary fibrosis, sarcoidosis, lymphangitic carcinomatosis, PCP. Kerley B lines: short horizontal lines at lung periphery perpendicular to pleura → interstitial edema (CHF). Pneumothorax: absence of lung markings beyond the visceral pleural line; lung edge visible; hyperlucency. Tension pneumothorax: tracheal deviation AWAY from pneumothorax + mediastinal shift + ipsilateral hemidiaphragm depression — clinical emergency.

C — Cardiac and D — Diaphragm

Cardiac: normal cardiothoracic (CT) ratio < 0.5 on PA film (heart width < half thoracic width); >0.5 = cardiomegaly. Heart failure on CXR (mnemonic ABCDE): A = Alveolar edema (bat-wing perihilar opacification), B = Kerley B lines (interstitial edema), C = Cardiomegaly, D = Diaphragm effusions (bilateral pleural effusions — right > left classically), E = Engorgement of upper-lobe vessels (cephalization — upper lobe veins more prominent than lower, reversal of normal). Pleural effusion: blunting of costophrenic angle (requires >200-300 mL); meniscus sign; complete haziness of hemithorax with mediastinal shift AWAY if large (tension effusion). Diaphragm: right hemidiaphragm normally 1.5-2.5 cm higher than left (gastric bubble below left). Flattened diaphragms = COPD/hyperinflation. Subphrenic air = pneumoperitoneum (free air under diaphragm = bowel perforation).