Left lower lobe consolidation

Left lower lobe consolidation refers to consolidation in part (incomplete) or all (complete) of the left lower lobe.

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 and includes:

• pneumonia
• adult respiratory distress syndrome (ARDS)
• interstitial pneumonias
• pneumonitis
• sarcoidosis

Radiographic features

Consolidation is usually obvious on CT, however features can be subtle on chest radiography. Features of left lower lobe consolidation on CXR include:

• opacification of the left upper, mid and/or lower zones
• normal (clear and distinct) left superior mediastinal contour (silhouette sign), especially the aortic arch
• obscuration of the left hilum, particularly the inferior hilum
• obscuration of the descending aortic contour (c.f. left upper lobe consolidation)
• normal (clear and distinct) left heart border (c.f. left upper lobe consolidation)
• obscuration of the left hemidiaphragm contour (c.f. left upper lobe consolidation)
• air bronchograms
• on lateral CXR: triangular opacification inferior and posterior to the left oblique fissure and obscuration of the left hemidiaphragm contour

It must be remembered that the homogeneity of the consolidation will be influenced by any underlying lung disease.

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

A mnemonic to remember the general features of consolidation is A2BC3.

Differential diagnosis

• left lower lobe collapse will show signs of volume loss