Left upper lobe consolidation

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

Pathology

Consolidation refers to the alveolar air spaces 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 with the anatomical location easy to define through visualization of the pleural fissures, however features can be subtle on chest radiography.

Plain radiograph

Features of left upper lobe consolidation on CXR include:

• opacification of the left upper zone and/or apex
• obscuration of the left superior mediastinal contour (silhouette sign), such as the aortic arch and left paratracheal stripe
• obscuration of the left hilum, particularly the superior hilum
• obscuration of the left heart border due to lingular consolidation
• normal (clear and distinct) descending aortic contour (c.f. left lower lobe consolidation)
• normal (clear and distinct) left hemidiaphragm contour (c.f. left lower lobe consolidation)
• air bronchograms
• on lateral CXR: triangular opacification superior and anterior to the left oblique fissure and normal (clear and distinct) left hemidiaphragm contour

General considerations

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 upper lobe collapse can be a subtle but classic diagnosis, with left lung veiling opacification and signs of volume loss