Cardiomegaly and pulmonary oedema on the chest X-ray
- Finding
In heart failure the heart looks big and fluid backs up into the lungs. The X-ray shows the fluid in a set order, from vessels to septa to air spaces.
What it is
Rising pressure in the left atrium and pulmonary veins shows on the chest X-ray in stages. First the upper-lobe vessels become as wide as or wider than the lower-lobe ones (upper-lobe diversion). Then fluid leaks into the interstitium: short horizontal lines at the lung bases (Kerley B lines), thickened fissures, cuffing around bronchi seen end-on and blurred hila. Finally fluid floods the alveoli: bilateral hazy opacity spreading from the hila (the bat-wing pattern), often with air bronchograms and bilateral effusions. The heart is often enlarged: a cardiothoracic ratio above 0.5 on a PA film. The order helps tell cardiogenic oedema from lung injury (ARDS).
What it looks like
- Cardiothoracic ratio: widest heart diameter over widest inner chest diameter; above 0.5 on an upright PA film is cardiomegaly.
- Stage 1, venous congestion: upper-lobe vessels equal to or wider than lower-lobe vessels.
- Stage 2, interstitial oedema: Kerley B lines (short, horizontal, at the bases, touching the pleura), peribronchial cuffing, thick fissures.
- Stage 3, alveolar oedema: bilateral perihilar bat-wing opacity, air bronchograms.
- Pleural effusions, usually bilateral and often larger on the right; fluid in a fissure can look like a mass.
- A globular, water-bottle heart with clear lungs suggests pericardial effusion rather than heart failure.
Why it looks that way
- Raised pulmonary venous pressure pushes fluid out of the capillaries into the interstitium, then into the alveoli.
- Kerley B lines are thickened interlobular septa filled with fluid, seen edge-on at the lung periphery.
- Upright, gravity normally makes lower-lobe vessels larger; congestion reverses that pattern.
Differential and pitfalls
- An AP or supine film magnifies the heart: do not call cardiomegaly on it, but a normal size on AP is truly normal.
- Poor inspiration crowds the bases and makes the heart look bigger.
- ARDS (non-cardiogenic oedema): normal heart size, no septal lines, more peripheral patchy opacity, few effusions.
- Bilateral pneumonia can look like oedema; fever, clinical course and quick response to treatment help separate them.
- Radiographic signs lag behind pressures: the film may look worse or better than the patient for hours to days.
Next step
- Echocardiography to measure ventricular function, valves and the pericardium.
- Natriuretic peptide, ECG and troponin as the clinical picture requires.
- Lung ultrasound at the bedside: several B-lines in both lungs support oedema and follow the response.
- Do not repeat the X-ray daily to follow treatment; repeat for a clinical change or a new problem.
- Big heart with clear lungs and low pressure or muffled sounds: urgent echo for pericardial effusion and senior review.
Test yourself
Think of the answer, then tap the question to see it.
Why should cardiomegaly not be diagnosed on an AP film?
The heart sits far from the detector and the beam diverges, so an AP film magnifies it; a normal size on AP, though, is reliable.
What are Kerley B lines?
Short horizontal lines at the lung bases that reach the pleura: interlobular septa thickened by fluid, a sign of interstitial oedema.
In what order do the X-ray signs of rising left atrial pressure appear?
Upper-lobe venous diversion, then interstitial oedema (Kerley B lines, cuffing, thick fissures), then alveolar oedema in a bat-wing pattern.
Which X-ray features favour ARDS over cardiogenic pulmonary oedema?
Normal heart size, no septal lines or upper-lobe diversion, patchy peripheral opacity and few or no effusions.
Connections
Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.
Sources: Cardiomegaly (StatPearls (NCBI Bookshelf), 2022); Pulmonary Edema (StatPearls (NCBI Bookshelf), 2023); Cardiogenic Pulmonary Edema (StatPearls (NCBI Bookshelf), 2023).
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Representative model, for educational purposes only.