Lobar consolidation is the term used to describe consolidation in one of the lobes of the lung. It implies an alveolar spread of disease and is most commonly due to pneumonia.
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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 the complete consolidation of a lobe, the most common cause is pneumonia. The 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:
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pulmonary malignancy
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bronchial obstruction with no (or minimal) collapse
bronchial stricture
foreign body
extrinsic compression from lymph nodes
Radiographic features
General features of consolidation on CXR include:
airspace opacification causing obscuration of pulmonary vessels
Specific lobar consolidation can be determined by the location of airspace opacification, pattern and the effect on adjacent structures (silhouette sign):
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right upper lobe consolidation
may obscure right paratracheal stripe
may outline the horizontal fissure below
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right middle lobe consolidation
may obscure the right heart border
may outline the horizontal fissure above
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right lower lobe consolidation
may obscure the right hemidiaphragm
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may obscure the left heart border
may obscure the left paratracheal stripe
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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
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