Lung Parenchyma

Airspace disease (i.e. consolidation) refers to a pathological process primarily in the alveoli. Differential diagnosis of consolidation includes:

1. Pus (pneumonia)
2. Blood hemorrhage
3. Cells (lung cancer or lymphoma)
4. Protein (alveolar proteinosis)
5. Fluid (pulmonary edema from interstitium)

Airways are not normally seen in a normal chest radiograph because they are an air structure within an aerated lung. When the aerated lung opacifies, the bronchii become visualized because of the surrounding contrast effect. These are called air bronchograms and are virtually diagnostic of consolidation.