Atelectasis is a condition of volume loss of some portion of the lung. It may be massive, with complete collapse of an entire lung or, more commonly, less extensive and involve a lobe, segment, or subsegment. Atelectasis results from a number of causes, which are illustrated in Figure 4.33.

' Obstructive atelectasis, the most common type, results when a bronchus is obstructed by a neoplasm, foreign body, or mucous plug (Fig. 4.46). Quite often, there is associated pneumonia distal to the site of obstruction.

' Compressive atelectasis is a purely physical phenomenon in which the normal lung is compressed by a tumor, emphysematous bulla, or an enlarged heart (Fig. 4.47).

Figure 4.45 Bronchiectasis. Thickened bronchial walls produce a tubular pattern in a patient with bronchiectasis (arrows).

Figure 4.46 Obstructive atelectasis on the left. There is complete collapse of the left lung caused by a central obstructing lesion in the left main-stem bronchus (arrow). The heart and mediastinum have shifted to the left.

Figure 4.47

Lung markings.

Compressive atelectasis in two patients with bullous emphysema. The large bullae in each lung compress and displace the remaining

Cicatrization atelectasis is produced by organizing scar tissue (Fig. 4.48). This occurs most often in healing tuberculosis (Tb) and other granulomatous diseases, as well as in entities such as pulmonary infarct and pulmonary trauma.

Adhesive atelectasis is a unique type of volume loss that occurs in the presence of patent airways. The mechanism involved is believed to be the inactivation of surfactant. A common example of this is hyaline membrane disease (HMD) (Fig. 4.49).

Passive atelectasis results from the normal compliance of the lung in the presence of either pneumothorax or pleural effusion. The airways remain patent (Fig. 4.50).

Figure 4.48 Cicatrization atelectasis. Scarring in the left lung has produced atelectatic changes in the left upper lobe. Note the left lower lung lucency indicating left lower lobe hyperinflation compensating for the collapsed left upper lobe.

Figure 4.49 Adhesive atelectasis in a premature newborn with hyaline membrane disease. There is a “ground glass"opacification to both lungs with air bronchograms (arrows).

Figure 4.50 Passive atelectasis.

There is partial collapse of the right lung in a patient with large right pneumothorax.

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