Lung Abscess versus Empyema

Coronal reformatted chest CT images show a lesion in the right upper lobe with internal air-filled cavity, thick irregular wall (green arrowheads) and another lesion in the left lower lung with internal fluid, thin wall (yellow arrowhead) and adjacent compression of the lung tissue (yellow arrows and box). The right upper lobe lesion is an abscess and the left lower lung lesion is an empyema.

Lung Abscess

• Localized suppuration with destruction of lung parenchyma
• Round, thick-walled cavity in areas of destroyed lung
• Typically irregular wall, irregular luminal margin and exterior surfaces
• Usually treated by prolonged antibiotics and postural drainage

Empyema

• Pus in the pleural cavity
• "Split pleural" sign: separation of uniformly thickened visceral pleura from parietal pleura
• Compression of uninvolved lung
• Usually require early tube drainage

Differentiating the Two

• Most specific signs: "split pleura" sign of empyema, compression of adjacent uninvolved lung in empyema
• Helpful signs: at least one wall of empyema is thin, uniform and smooth on both luminal margin and exterior surface
• Less reliable sign: size, shape (oval vs round), chest wall angle (obtuse vs acute)

Reference:

Stark DD, Federle MP, Goodman PC, et al. Differentiating lung abscess and empyema: radiography and computed tomography. AJR 1983;141:163-167.

Follow RiTradiology on Facebook, Twitter or Google Friend Connect

Visit RiT Illuminations to view nice pictures from your colleague