IS Case 155: Empyema with bronchopleural fistula
Imaging Sciences URMC 2008
Publication Date: 2009-05-21
A selected axial post-contrast CT view demonstrates a large loculated right pleural fluid collection containing an air-fluid level. The surrounding pleura are thickened and enhancing. A bronchus originating from the right lower lobe communicates with the pleural space. The right lower lobe is collapsed. Pleural fluid culture grew S. Aureus.
Empyema is differentiated from simple effusion according to pleural fluid analysis. Simple effusions do not demonstrate frank pus and are culture or Gram stain negative for organisms. Empyemas are usually grossly purulent, demonstrate a high pleural neutrophil count or a low pH, or are culture or Gram stain positive. While simple effusions may be treated conservatively with antibiotics or an underlying pulmonary infection, empyemas require chest tube drainage in addition to antibiotics.
Empyemas develop in three distinct phases: exudative, fibrinopurulent, and organizing. During the exudative phase, inflammation of the visceral pleura results in weeping of fluid into the pleural space. Soon after, a fibrinopurulent phase ensues in which inflammatory cells accumulate in the pleural space and fibrin is deposited on the inflamed pleural surfaces. At this stage, CT may show a “split pleura” sign, i.e., thickened visceral and parietal pleura separated by fluid, and demonstrating contrast enhancement. The “split pleura” sign is not specific for empyema, but is indicative of an exudative effusion, whether it is due to infection, neoplasm, or inflammatory disease. In the organizing phase, the deposition of collagen and granulation tissue along the visceral and parietal surfaces results in pleural fibrosis.
It is important to distinguish empyema from pleural abscess, as they have different treatment implications. CT findings favoring empyema include an oblong fluid collection with smooth inner margins that compresses and displaces the surrounding lung and airways away from the pleural collection. Findings favoring abscess include a thick-walled, spherical cavity that destroys the lung. Consolidated lung surrounds the cavity, and air bronchograms travel through the area instead of being displaced. Lung abscesses tend to form acute angles with the pleura.
Empyema may be complicated by the presence of a bronchopleural fistula. A bronchopleural fistula should be suspected whenever the chest radiograph reveals an air-fluid level or when the patient expectorates copious quantities of sputum while lying on one side, and not while lying on the other side. It may be difficult to diagnose on plain film, and further analysis with CT is often helpful. A bronchopleural fistula is present when a communication between the pleural space and an airway or the lung parenchyma can be demonstrated. Causes of bronchopleural fistula include necrotizing pneumonia, bronchiectasis, malignancy, surgery, and trauma.
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