Lung abscess is a necrotic inflammatory disease of the lung caused by different pathogens. The infection route includes inhalation of pathogens from the mouth and nose, hematogenous dissemination often secondary to infection in other parts of the body, and direct extension of infection in adjacent organs.
Clinical presentation and pathology
Pathological change is abscess cavity formed by liquefied necrotized lung tissue coughed up from the bronchi due to bronchiolar obstruction, inflammatory embolism of small vessels, and necrosis of lung tissue resulting from suppurative pneumonia; sometimes the abscess ruptures into the chest cavity, forming pyopneumothorax and bronchopleural fistula. In the acute stage, the abscess cavity can reduce and subside through postural drainage and antibiotic treatment. If there is protracted course, the disease can progress into chronic lung abscess.
The clinical manifestations are acute onset, rigors, high fever, and thoracodynia; cough is gradually exacerbated, large amounts of purulent and smelly sputum can be coughed up, and the total count of white blood cells in the blood increases significantly. In chronic lung abscess, patients often present with cough, purulent and bloody sputum, irregular fever, anemia, and emaciation, with or without clubbed fingers (toes).
Imaging manifestations
X-ray
There may be solitary or multiple lesions, and multiple lesions are common in hematogenous lung abscesses. In the early stage, there is dense massive opacity in the lungs, and then thick-walled cavity is formed; the inner wall is often smooth, and air-fluid level is often seen at the bottom. In acute lung abscess, due to inflammatory infiltration around the abscess, hazy exudative opacity is often seen around the cavity wall. In chronic lung abscess, the resorption of inflammatory infiltration around the abscess is reduced, the cavity wall is thinned, the cavity is also reduced, and there are some peripheral, disordered, irregular linear lesions.
Figure 1 Lung abscess
Chest x-ray film shows a large thick-walled cavity in the right lower lung, with smooth inner edge, air-fluid level, and hazy outer edge.
CT
CT is better than x-ray in visualization of the abscess wall, can show whether there are early necrosis and liquefaction in consolidation, and can determine whether the abscess is in the lung or pleural cavity, whether there is little pleural effusion, and whether there is local pleural thickening at the abscess site. In addition, CT can also determine whether the lung abscess ruptures into the pleural cavity to form localized empyema or pyopneumothorax. Contrast-enhanced CT shows significantly enhanced abscess wall.
Figure 2 Lung abscess
Contrast- enhanced CT shows a thick-walled cavity in the right lower lung, with air-fluid level and significantly enhanced wall of the cavity (↗).
Diagnosis and differential diagnosis
Lung abscess cavity needs to be differentiated from cancerous cavity and tuberculosis cavity. Cancerous cavity is more common in older patients and often thick-walled and eccentric; the inner wall is rough, with or without wall nodule; the outer wall may have lobulation sign and spiculation sign; enlarged hilar and mediastinal lymph nodes are often accompanied. Tuberculous cavity mostly occurs in the apical segment and posterior segment of the upper lobe and dorsal segment of the lower lobe, usually small, thin-walled; the inner wall is smooth; and there are often peripheral satellite lesions.