Why a Systematic Approach to X-rays is Necessary
Gross changes on a plain chest X-ray — massive hydrothorax, radiopaque foreign body — are detected without difficulty. Difficulties arise when searching for subtle changes: sarcoidosis, small pneumothorax, rib fractures, early infiltrates. To avoid missing such findings, a standardized ABCDE algorithm is used, which allows for a systematic evaluation of the radiograph in 5–10 minutes covering all anatomical zones.
A — Airway: Airways
Evaluation begins not with the lung fields, but with the air-conducting structures. Three objects are analyzed sequentially:
- Trachea — its position along the midline. Displacement may occur due to pushing (massive pleural effusion, tension pneumothorax) or pulling (collapse or atelectasis of a lung lobe).
- Tracheal bifurcation (carina) and main bronchi — a frequent location for foreign bodies; sometimes the outlines of a swallowed object (e.g., a dental crown) and associated atelectasis can be distinguished.
- Roots of the lungs (hila) — right and left. Widening and hardening of the roots may indicate sarcoidosis, lymphadenopathy, or a neoplastic process.
B — Breathing: Lungs and Pleura
Only after assessing the airways are the lung fields analyzed. The pulmonary patterns on the right and left are compared. Density landmark: anything approaching the intensity of bone is classified as fluid, infiltrate, or a soft tissue mass.
- Consolidation — an area of opacification due to fluid, inflammatory exudate, or infiltrate (e.g., upper lobe pneumonia).
- A mass lesion with irregular borders is a reason to suspect central lung cancer.
- Absence of the pulmonary pattern out to the chest wall is a sign of pneumothorax; the visceral pleural line and collapsed lung are visible. If a pneumothorax is detected, a targeted search for a rib fracture is mandatory.
- Nodular deposits on the pleura ("droplets") are suspicious for mesothelioma.
- Free fluid in the pleural space forms a characteristic Ellis–Damoiseau line.
C — Cardiac: Heart and Mediastinum
Normally, the transverse diameter of the heart does not exceed 50% of the chest width on a posteroanterior view (cardiothoracic ratio). Exceeding this value is termed cardiomegaly. Next, the contours are analyzed sequentially: right atrium, left ventricle, aortic arch, pulmonary trunk. Evaluating the contours helps suspect dilation of specific chambers and great vessels.
D — Diaphragm: Diaphragm and Subdiaphragmatic Space
Anatomical norm: the right dome of the diaphragm is located higher than the left, and the gastric air bubble is visualized under the left dome. The contour of the diaphragm normally adheres tightly to the liver and is not separated from it.
- Crescent sign — a sickle-shaped strip of gas under the dome of the diaphragm. Indicates pneumoperitoneum and, as a rule, perforation of a hollow viscus — a condition requiring emergency surgical intervention.
- Pseudopneumoperitoneum in Chilaiditi syndrome: interposition of the colon between the liver and diaphragm mimics free gas. When in doubt, a radiology consultation is mandatory.
- Costophrenic angles are normally sharp. Blunting of the angle is observed with pleural effusion or lung hyperinflation due to COPD (flattening of the diaphragmatic domes, barrel chest on the lateral view).
E — Everything else: Other Structures
At the final stage, structures that account for about 5% of diagnoses but are critically important for the completeness of the report are evaluated.
- Mediastinum: aortic knob (the convexity of the aortic arch along the left contour) — its enlargement is characteristic of an aortic aneurysm. Aortopulmonary window between the aortic arch and the pulmonary artery; its disappearance indicates lymphadenopathy or a mediastinal mass process.
- Bones: integrity of the ribs, clavicles, sternum, spine; lytic lesions and osteolysis as signs of metastatic involvement.
- Soft tissues: asymmetry, breast shadow, hematomas, disseminated changes (miliary tuberculosis, disseminated cancer).
- Foreign devices: position of the endotracheal and nasogastric tubes (the latter should reach the stomach and not end in the bronchus), central venous catheters, artificial heart valves, pacemaker leads, sternotomy wires.
Key points
- The ABCDE algorithm ensures a systematic review of the radiograph and reduces the risk of missing pathology.
- Evaluation begins with the airways, not the lung fields — this is a major common mistake made by students.
- Tracheal displacement is differentiated into "pushing" (effusion, tension pneumothorax) and "pulling" (atelectasis) causes.
- When a pneumothorax is detected, searching for a rib fracture is mandatory.
- A cardiothoracic ratio greater than 50% is a criterion for cardiomegaly.
- The crescent sign under the diaphragm is a sign of pneumoperitoneum and an indication for emergency evaluation of the hollow viscus.
- Blunting of the costophrenic angle occurs with effusion or lung hyperinflation in COPD.
- At stage E, the aortic knob, aortopulmonary window, bones, soft tissues, and foreign devices are evaluated.