Recognizing Lobar Collapse on a Standard Chest Radiography

There are two general types of pulmonary atelectasis, compressive and resorptive. Fundamental differences between the pathophysiology of these two forms are reflected in the different radiographic appearances of each. This review will provide a basis to recognize atelectasis and to distinguish lobar collapse from resorptive atelectasis on a standard posteroanterior and a lateral chest radiograph. A systematic approach to evaluating chest radiographs is advised based on three questions: Do the lungs, or does a lung, appear small? Are thoracic or extrathoracic structures shifted from their usual position? Is there a characteristic soft tissue density pattern within the lungs? Atelectasis may be identified directly by making an assessment of reduced lung volume on the standard chest radiograph and indirectly inferred by shifts of thoracic and extrathoracic structures from their usual positions. Increased soft tissue density is also an integral component of lobar atelectasis. As residual air is resorbed and the lobe collapses, the soft tissue component of the lobe projects a characteristic pattern on the posteroanterior and the lateral chest roentgenogram. Recognizing lobar collapse on the standard posteroanterior and the lateral chest radiograph should lead to further diagnostic techniques for evaluating the patency of the proximal tracheobronchial tree.