Chest Imaging

Actinomycosis

infection caused by a slow growing Gram-positive bacterium, Actinomyces israelii, which because of branching mycelial formation may resemble a fungus and at one time was classified as such. These organisms are found as saprophytes in the oropharynx, producing infection when placed into contact with necrotic or lacerated tissue. Most cases involve the cervicofacial or abdominal region with access to the thorax either by aspiration or direct spread through fascial planes from the mediastinum or across the diaphragm. Clinically patients may present with a productive cough, or mediastinal and pleural involvement may lead to chest pain or occasionally signs of pericarditis. In untreated cases soft tissue masses or sinus tracts with "sulphur granules" (mycelia) may be observed. Diagnosis may be difficult, anaerobic culture and occasionally tissue biopsy are necessary.

The chest radiograph demonstrates an area of peripheral homogeneous opacity simulating conventional bacterial pneumonia or perhaps neoplasm (Fig.1). Cavitation and adjacent pleural fluid collections were common prior to the advent of modern antibiotics, as were sinus tracts in the chest wall and evidence of rib involvement such as lytic lesions and/or chronic periostitis. Hilar lymphadenopathy is unusual, although mediastinal enlargement may occur particularly with direct extension from the cervicofacial region. With appropriate therapy resolution of actinomycosis pneumonia is expected without complication. If antibiotic therapy is intermittent or incomplete chronic fibrotic changes may result.

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Fig.1

A PA chest film demonstrates pleural thickening and heterogeneous lung opacities which had been present for several weeks. Along the midlateral hemithorax increased opacity can be identified in the soft tissues at the site of a fistula from the pleural space.
Actinomycosis, Fig.1