consolidation

Consolidation is what you see when a region of lung that should be full of air becomes filled instead with something denser — fluid, pus, blood or cells. A healthy lung is mostly air and looks dark on imaging; a consolidated lung is like a sponge that has soaked up water, so on X-ray or CT that area turns solid and white.

Because the air spaces are now packed with material, X-rays no longer pass through easily and the underlying blood vessels are obscured — a key way to tell consolidation apart from the lighter haze of ground-glass opacity, where vessels remain visible. A classic clue is the “air bronchogram”: dark branching airways still containing air standing out against the surrounding whiteness.

The most common cause is pneumonia, where infected fluid and immune cells flood the air sacs, but consolidation is a pattern rather than a single disease. It can also result from fluid in heart failure, blood from haemorrhage, aspirated material, or certain tumours and inflammatory conditions. The pattern's distribution, how quickly it appears and the clinical setting guide what is actually going on.