With a primary lung abscess, oropharyngeal contents are aspirated (generally while the patient is unconscious) and contain mixed flora.2 The aspirate typically migrates to the posterior segments of the upper lobes and to the superior segments of the lower lobes. These abscesses are usually singular and have an air-fluid level.1,2
Secondary lung abscesses occur in bronchial obstruction (by tumor, foreign body, or enlarged lymph nodes), with coexisting lung diseases (bronchiectasis, cystic fibrosis, infected pulmonary infarcts, lung contusion) or by direct spread (broncho-esophageal fistula, subphrenic abscess).6 Secondary abscesses are associated with a poorer prognosis, dependent on the patient’s general condition and underlying disease.7
What to rule out
The differential diagnosis of cavitary lung lesion includes tuberculosis, necrotizing pneumonia, bronchial carcinoma, pulmonary embolism, vasculitis (eg, Churg-Strauss syndrome), and localized pleural empyema.1,4 A CT scan is helpful to differentiate between a parenchymal lesion and pleural collection, which may not be as clear on CXR.1,4
Tuberculosis manifests with fatigue, weight loss, and night sweats; a chest CT will reveal a cavitating lesion (usually upper lobe) with a characteristic “rim sign” that includes caseous necrosis surrounded by a peripheral enhancing rim.8
Necrotizing pneumonia manifests as acute, fulminant infection. The most common causative organisms on sputum culture are Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas species. Plain radiography will reveal multiple cavities and often associated pleural effusion and empyema.9
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