Lobar consolidation

Lobar consolidation is the term used to describe consolidation in one of the lobes of the lung. It infers an alveolar spread of disease and is most commonly due to pneumonia.

Pathology

Consolidation refers to the alveolar airspaces being filled with fluid (exudate/transudate/blood), cells (inflammatory), tissue, or other material.

The list of causes of consolidation is broad but for complete consolidation of a lobe, the most common cause is pneumonia. Infection spreads through the lobe through the pores of Kohn between alveoli but is limited from spreading between lobes by the visceral pleura.

Other causes include:

• pulmonary malignancy
  • adenocarcinoma
  • lymphoma
• bronchial obstruction with no (or minimal collapse)
  • endobronchial neoplasm
  • bronchial stricture
  • foreign body
  • extrinsic compression from lymph nodes
• pulmonary hemorrhage
• pulmonary alveolar proteinosis

Radiographic features

General features of consolidation on CXR include:

• airspace opacification causing obscuration of pulmonary vessels
• air bronchograms

Specific lobar consolidation can be determined by the location of airspace opacification, pattern and the effect on adjacent structures (silhouette sign):

• right upper lobe consolidation 
  • may obscure right paratracheal stripe
  • may outline the horizontal fissure below 
• right middle lobe consolidation
  • may obscure the right heart border
  • may outline the horizontal fissure above
• right lower lobe consolidation
  • may obscure the right hemidiaphragm
• left upper lobe consolidation
  • may obscure the left heart border
  • may obscure the left paratracheal stripe
• left lower lobe consolidation
  • may obscure the left hemidiaphragm
  • may obscure the descending aorta

It must be remembered that the homogeneity of the consolidation will be influenced by any underlying lung disease. For example, consolidation in background emphysematous lung is very often non-confluent. 

Occasionally with complete lobar consolidation, there may be an increased volume of the affected lobe, rather than the more frequent neutral or reduced volume. When the fissures are outwardly convex, the appearance is referred to as the bulging fissure sign.

Differential diagnosis

• lobar collapse can be mistaken for lobar consolidation but collapse will show signs of volume loss and usually absence of air bronchograms