Introduction
This topic covers the imaging of nonspecific inflammatory lung diseases: pneumonia (lobar, bronchopneumonia, staphylococcal, viral) and lung abscess, with the distinction between bacterial and viral pneumonia.
Pneumonia
Pneumonia is a lung infection with purulent material that fills the alveoli. It can be primary (in healthy patients) or secondary (in those with underlying disease). Most are bacterial, and Streptococcus pneumoniae is the most common; secondary pneumonia may be congestive, hypostatic, aspiration pneumonia, etc. Alveolar consolidation does not occur only in bacterial pneumonia but also in pulmonary oedema and haemorrhage (differential diagnosis). Complications are identified on CT.
Lobar pneumonia
Classically caused by streptococcus. In stage 1 there is an enhanced lung pattern and decreased transparency due to hyperaemia; in stages 2 and 3 there is consolidation with increased volume of the area; in the 4th stage the shadow decreases in size and intensity. Triangular opaque shadow.
Bronchopneumonia
Inflammation of the bronchi, bronchioles and peribronchial space; multiple foci, bilateral; progression involves nearby lobules. On CXR there are multiple irregular spotty opacities (infiltrates); on CT there are many foci of consolidation (hyperdense) and tree-in-bud changes.
Complications of pneumonia
- Cavities when necrosis occurs.
- Abscesses.
- Pneumatocele: cystic lesion filled with air, of varying size and appearance.
- Pleural effusion, due to increased permeability of the visceral pleura near the inflammation; more common in bacterial pneumonia.
- Pleural empyema and abscess.
Staphylococcal pneumonia
Focal pneumonia with a tendency to form pleural empyema, abscesses and cavities, which can rupture and cause pneumothorax.
Viral pneumonia
The interstitium is primarily affected; on CXR there are reticular-nodular shadows, decreased transparency and sometimes a ground-glass appearance. Example: COVID-19. HRCT is the choice for staging and follow-up, CXR for screening. Ground-glass opacities are seen bilaterally, subpleural and peripheral, which later can become crazy paving; consolidation and bronchiectasis can be seen too.