Pyothorax, also known as empyema, is caused by mostly direct spread of infection in adjacent organs, but also hematogenous dissemination of distant infection.
Clinical presentation and pathology
In the acute phase, there may be high fever, tachypnea, and thoracodynia. In the chronic phase, the manifestations are mainly the symptoms of chronic wasting disease. Pyothorax can be tuberculous and non-tuberculous. The former is mainly caused by the rupture of caseous lesions or tuberculous cavities into the pleural cavity, or the invasion of tuberculous lesions into the pleural cavity through the lymphatic channels. The latter can be caused by pleural involvement resulting from lung abscess, lobar pneumonia, and segmental pneumonia. The involved pleural cavity can cause pleural empyema, and the locally thickened visceral and parietal pleura constitutes the wall of the abscess cavity, eventually leading to pleural thickening, adhesion, and calcification. Thoracic collapse may occur.
Imaging manifestations
X-ray
In the acute stage, the main manifestations are free pleural effusion or encapsulated effusion, some patients have bronchopleural fistula, and air-fluid level can be seen. In the chronic stage, the main manifestations are pleural thickening, adhesion, and even calcification, resulting in narrowed intercostal space on the affected side, thoracic collapse, mediastinum shifting to the affected side, and diaphragm rising; some patients may have periosteal reaction in the adjacent ribs due to inflammatory stimulation.
CT
On plain CT, the density of pleural effusion in pyothorax is slightly higher than that of general exudative pleural effusion, air opacities can be seen in some patients, and the wall of empyema is thick and homogeneous; the adjacent lung parenchyma is compressed and displaced. On contrast-enhanced CT, the wall of the abscess cavity is annular and significantly homogeneously enhanced, and the inner wall is smooth.
Figure 1 Pyothorax
Plain CT shows the density at the center of the lesion (↗) is slightly higher than that of water, there is air opacity, and the peripheral wall is very thick.
Diagnosis and differential diagnosis
Pyothorax is mainly manifested by pleural effusion, but encapsulation and pleural thickening can be formed. It is not difficult to diagnose with typical clinical manifestations. Pyothorax is mainly differentiated from peripheral lung abscess. Lung abscess has unclear edges in the acute stage, and is often accompanied by exudative lesions in the lungs; in addition, the wall thickness of lung abscess may be inhomogeneous.