Air-space opacification (summary)

Air-space opacification is a descriptive term that refers to filling of the pulmonary tree with material that attenuates x-rays more than the surrounding lung parenchyma. It is equivalent to the pathological diagnosis of pulmonary consolidation.

Reference article

This is a summary article; read more in our article on air space opacification.

Summary

• pathophysiology
  • material fills the pulmonary tree
    • fluid: pulmonary oedema 
    • pus: pneumonia
    • blood: pulmonary haemorrhage
    • cells: cancer
    • protein: alveolar proteinosis (rare)
• investigation
  • chest x-ray
    • confirmation of consolidation and additional findings
    • assessment of:
      • severity, e.g. number of lobes involved
      • accompanying pathology, e.g. effusion
      • complications, e.g. abscess formation
  • CT chest
    • air space opacification looks very similar to the chest x-ray
    • distribution can be assessed more accurately
    • assessment of associated features is more accurate

Radiographic features

Plain radiograph

Consolidated areas are radio-opaque on chest radiograph and chest CT compared to normally air-filled lung tissue. The distribution pattern of consolidation can aid in narrowing the potential differential diagnosis.

Patchy

The air-space filling is only partial and there is, therefore, residual gas within the alveoli. 

Lobar

Where increased density/opacity is seen in individual lung lobes. Sharp delineation can be seen when consolidation reaches a fissure. Air bronchograms can also be seen where air-filled bronchi are visible against the dense diseased tissue. Volume loss is not usually seen.

Diffuse

Most commonly due to heart failure, resulting in other signs such increased cardiac size, Kerley B-lines, redistribution on pulmonary blood flow and pleural fluid.

Multi-focal

Multiple areas of opacity seen throughout the lung most often are due to bronchopneumonia, starting from bronchi and spreading outwards. Usually ill-defined with peripheral distribution. Neoplasms such as a primary malignancy or metastasis can also cause this picture.