Fig 1A Fig 1B

Fig 1C

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Findings: There is a well defined rounded cavitary mass in the left lower lobe. There is an air fluid level within the mass (1a-1b). Adjacent lung consolidation is present. There is parenchymal opacity involving the posterior segment of the right upper lobe (Fig. 1c).

Diagnosis: Lung abscess secondary to aspiration pneumonia

Discussion: This case illustrates the radiologic features of a parenchymal lung abscess. The radiological distinction between empyema and lung abscess is crucial, as the treatment is significantly different for these two processes. Classically, there are three major features that distinguish lung abscess from empyema. In lung abscess, an acute angle is formed with the adjacent lung parenchyma, while an empyema has an obtuse angle. While the empyema tends to displace the lung parenchyma away, the lung abscess causes lung destruction. The most important distinction is the dimensions of the fluid or air/fluid collection in the PA and lateral projection. Lung abscess will have a longer AP dimension, best seen in the lateral view, while the lung abscess will be rounded in configuration in both views.

This distinction is important because the treatment for lung abscess and empyema is significantly different. In empyema, treatment is tube drainage and/or decortication of the pleural space. In lung abscess, percutaneous drainage can result in pleural seeding and possibly empyema. Medical management with antibiotics is the treatment of choice in lung abscess.

References:
Kuhlman J. Complex Disease of the Pleural Space.
Radiographics. 1997;17:1043-1050.

McLoud TC, Flower CDR.Imaging the Pleura:
Sonography, CT and MRImaging. AJR 1991;145:1145-1153.

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