Clinical meaning
Chest X-ray interpretation requires a systematic approach to avoid missed findings. The standard PA (posteroanterior) film is taken with the patient standing 6 feet from the X-ray source, with the anterior chest against the cassette, minimizing cardiac silhouette magnification. AP (anteroposterior) films, often portable, magnify the heart and mediastinum, making cardiomegaly assessment unreliable. X-ray images display five densities from most to least radiopaque: metal (white) > bone > soft tissue/fluid > fat > air (black). The systematic ABCDE approach covers: Airway (tracheal position, carina), Breathing (lung fields, pleural spaces), Cardiac (heart size, mediastinal contours), Diaphragm (costophrenic angles, free air), and Everything else (bones, soft tissues, tubes/lines). The silhouette sign occurs when two adjacent structures of the same density lose their border (e.g., right heart border loss = RML pathology; left heart border loss = lingula pathology).
Diagnosis & workup
Diagnostics & workup: - Systematic ABCDE approach: Airway (trachea midline? deviation suggests tension pneumothorax, large effusion, or mass), Breathing (compare lung fields for symmetry, opacities, hyperinflation), Cardiac (heart width <50% of thoracic width on PA = normal; >50% = cardiomegaly), Diaphragm (R normally higher than L; blunted costophrenic angles = effusion >200-300 mL), Everything else (bones, soft tissues, tubes/lines) - Air bronchograms: air-filled bronchi visible within opacified (consolidated) lung parenchyma -- indicates alveolar filling (pneumonia, pulmonary edema, ARDS) - Silhouette sign: loss of normal border between structures of similar density indicates adjacent pathology (loss of R heart border = RML; loss of L heart border = lingula; loss of R hemidiaphragm = RLL; loss of L hemidiaphragm = LLL) - Meniscus sign: concave upper border of pleural effusion on upright film; fluid levels with hydropneumothorax - Kerley B lines: short horizontal lines at lung periphery indicating interstitial edema (pulmonary venous congestion) - Deep sulcus sign: deep costophrenic angle on supine film indicating anterior pneumothorax