Air space opacification

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

In radiological studies, it presents as increased attenuation of the lung parenchyma causing obscuration of pulmonary vessels, without significant loss of volume, in the segment(s) affected. Air bronchograms can also be found ^1,2.

Pathology

Etiology

The opacification is caused by fluid or solid material within the airways that causes a difference in the relative attenuation of the lung:

• transudate, e.g. pulmonary edema secondary to heart failure
• pus, e.g. bacterial pneumonia
• blood, e.g. pulmonary hemorrhage
• cells, e.g. bronchoalveolar carcinoma
• protein, e.g. alveolar proteinosis
• fat, e.g. lipoid pneumonia
• gastric contents, e.g. aspiration pneumonia
• water, e.g. drowning

When considering the likely causes of airspace opacification, it is useful to determine chronicity (by reviewing previous radiographs) and considering laterality.

Additionally, the presence of mediastinal or hilar lymphadenopathy further refines the massive list of differentials:

• acute unilateral air space opacification
• acute bilateral air space opacification
• acute airspace opacification with lymphadenopathy
• chronic unilateral airspace opacification
• chronic bilateral airspace opacification

Patterns of disease

On chest radiography a number of patterns are recognized:

• lobar consolidation
  • right upper lobe consolidation
  • right middle lobe consolidation
  • right lower lobe consolidation
  • left upper lobe consolidation
  • left lower lobe consolidation
• bronchopneumonia
• lobar lung collapse
  • right upper lobe collapse
  • right middle lobe collapse
  • right lower lobe collapse
  • left upper lobe collapse
  • left lower lobe collapse