Lung Abscess Workup

• A complete white blood cell count with differential may reveal leukocytosis and a left shift.
• Obtain sputum for Gram stain, culture, and sensitivity.
• If tuberculosis is suspected, acid-fast bacilli stain and mycobacterial culture is requested.
• Blood culture may be helpful in establishing the etiology.
• Obtain sputum for ova and parasite whenever a parasitic cause for lung abscess is suspected.

• Chest radiography^[8]

  • A typical chest radiographic appearance of a lung abscess is an irregularly shaped cavity with an air-fluid level inside. Lung abscesses as a result of aspiration most frequently occur in the posterior segments of the upper lobes or the superior segments of the lower lobes.
  • The wall thickness of a lung abscess progresses from thick to thin and from ill-defined to well-circumscribed as the surrounding lung infection resolves. The cavity wall can be smooth or ragged but is less commonly nodular, which raises the possibility of cavitating carcinoma.
  • The extent of the air-fluid level within a lung abscess is often the same in posteroanterior or lateral views. The abscess may extend to the pleural surface, in which case it forms acute angles with the pleural surface.
  • Anaerobic infection may be suggested by cavitation within a dense segmental consolidation in the dependent lung zones.
  • Lung infection with a virulent organism results in more widespread tissue necrosis, which facilitates progression of underlying infection to pulmonary gangrene.
  • Up to one third of lung abscesses may be accompanied by an empyema. See the images below.Pneumococcal pneumonia complicated by lung necrosis and abscess formation. A lateral chest radiograph shows air-fluid level characteristic of lung abscess. A 54-year-old patient developed cough with foul-smelling sputum production. A chest radiograph shows lung abscess in the left lower lobe, superior segment. A 42-year-old man developed fever and production of foul-smelling sputum. He had a history of heavy alcohol use, and poor dentition was obvious on physical examination. Chest radiograph shows lung abscess in the posterior segment of the right upper lobe. Chest radiograph of a patient who had foul-smelling and bad-tasting sputum, an almost diagnostic feature of anaerobic lung abscess.
• Computed tomography^{[8, 9]}

  • CT scanning of the lungs may help visualize the anatomy better than chest radiography. CT scanning is very useful in the identification of concomitant empyema or lung infarction.
  • On CT scans, an abscess often is a rounded radiolucent lesion with a thick wall and ill-defined irregular margins.
  • The vessels and bronchi are not displaced by the lesion, as they are by an empyema.
  • The lung abscess is located within the parenchyma compared with loculated empyema, which may be difficult to distinguish on chest radiographs.
  • The lesion forms acute angles with the pleural surface chest wall. See the image below.A 42-year-old man developed fever and production of foul-smelling sputum. He had a history of heavy alcohol use, and poor dentition was obvious on physical examination. Lung abscess in the posterior segment of the right upper lobe was demonstrated on chest radiograph. CT scan shows a thin-walled cavity with surrounding consolidation.
• Ultrasonography

  • Peripheral lung abscesses with pleural contact or included inside a lung consolidation are detectable using lung ultrasonography at the bedside.
  • Lung abscess appears as a rounded hypoechoic lesion with an outer margin.
  • If a cavity is present, additional nondependent hyperechoic signs are generated by the gas-tissue interface.^[10]

Diagnostic material uncontaminated by bacteria colonizing the upper airway may be obtained for anaerobic culture from the following:

• Blood culture
• Pleural fluid (if empyema present)
• Transtracheal aspirate
• Transthoracic pulmonary aspirate
• Surgical specimens
• Fiberoptic bronchoscopy with protected brush
• Bronchoalveolar lavage with quantitative cultures

Expectorated sputum and other methods of sampling the upper airway do not yield useful results for anaerobic culture because the oral cavity is extensively colonized with anaerobes. Blood cultures are infrequently positive in patients with lung abscess, and empyema is rare.

The other modalities listed are invasive, costly, and require laboratory expertise. Bronchoscopy using a protected brush to obtain a specimen uncontaminated by the upper airway or quantitative culture of organisms from the bronchoalveolar lavage fluid has been advocated to establish bacteriologic diagnosis in lung abscess. However, the experience with this technique in diagnosis of anaerobic lung infections is limited and the diagnostic yield is uncertain. Perhaps most importantly, cultures obtained by any of these methods are unlikely to be positive after the initiation of antibiotics.^[11]

Flexible fiberoptic bronchoscopy is performed to exclude bronchogenic carcinoma whenever bronchial obstruction is suspected.^[12]

Lung abscesses begin as small zones of necrosis developing within the consolidated segments in pneumonia. These areas may coalesce to form single or multiple areas of suppuration, which are referred to as lung abscesses. If antibiotics interrupt the natural history at an early stage, the healing results in no residual changes. When the progressive inflammation erodes into the adjacent bronchi, the contents of the abscess are expectorated as malodorous sputum. Subsequently, fibrosis occurs, which causes a dense scar and separates the abscess. The abscess may still occur, and spillage of pus into the bronchial tree may disseminate the infection.

See the images below.