Obstructive emphysema is overinflation and abnormal dilation of the air-containing spaces distal to terminal bronchioles, with irreversible destruction of the alveolar wall. Emphysema can be divided into localized and diffuse emphysema. In localized obstructive emphysema, partial bronchial obstruction results in one-way valve effect, the bronchial expansion allows air to enter during inspiration, and the air cannot be completely exhaled during exhalation, leading to overinflation of distal alveoli. In diffuse obstructive emphysema, diffuse chronic inflammation and stenosis of the terminal bronchioles result in valvular expiratory obstruction, and the alveoli of the distal terminal bronchioles are overinflated and accompanied by destruction of alveolar wall.
X-ray
On the frontal chest radiograph, localized obstructive emphysema is manifested by localized increased lucency of the lung field, and the range depends on the location of the obstruction. Emphysema in one lung or one lobe is manifested by increased lucency of one lung or one lobe, decreased lung markings, mediastinum shifted to the healthy side, and diaphragm descended on the diseased side.
On the frontal chest x-ray film, diffuse obstructive emphysema is manifested by generally increased lucency of lung fields, often with bullae and decreased lung markings. In the late stage, lung markings are thinned and reduced, lung field lucency is significantly increased, anteroposterior and transverse diameters of the thorax are enlarged, intercostal space widens, diaphragm is flattened and mobility is weakened, the heart opacity is narrow and long, suspended heart is present, central pulmonary artery can be thickened, peripheral pulmonary blood vascular markings are thinned, and pulmonary hypertension and cor pulmonale may occur in severe patients.
Figure 1 Emphysema in lower lungs
Chest film shows increased lucency (↗) in the bilateral lower lung fields, decreased pulmonary markings, widened intercostal spaces, and flattened diaphragm.
CT
In localized obstructive emphysema, CT shows increased localized lung lucency and decreased lung markings. CT is more sensitive than x-ray to detect localized emphysema, and can show the location of obstruction and even the cause of obstruction.
In diffuse obstructive emphysema, lung markings of both lungs are generally decreased, thinned, and straightened; the rest of the manifestations are the same as those seen on chest x-ray film.
Figure 2 Emphysema in the left lower lobe
CT lung window shows increased lucency and decreased lung markings (↗) in the left lower lobe
Thin-section high-resolution CT can show the structure and abnormal changes of pulmonary lobules, and can detect early emphysema.