The pulmonologist and radiologist commonly recognize a variety of abnormal patterns of diffuse parenchymal lung disease on the conventional chest radiograph. Identification of these patterns, along with recognition of other associated findings, can be extremely useful in guiding the development of a differential diagnosis . The diagnostic approach to diffuse lung disease based on interpretation of the conventional chest radiograph will be discussed here, using examples to illustrate many of the radiographic features.
CRITIQUE OF PATTERN USE
The traditional approach to radiographic assessment of diffuse lung disease first involves determining whether the pulmonary parenchymal process is located within the interstitium or the alveolar spaces. However, although radiographic criteria for both types of processes have been established over the years, the correlation is relatively poor between the accuracy of the radiologic localization (to either the airspaces or the interstitium) and the actual pathologic findings. Specific issues include the following:
●Nodular patterns can be produced by either interstitial or alveolar disease.
●Interstitial pneumonias usually also involve the alveolar compartment.
●So-called alveolar disease regularly involves the interstitium as well. The paradigm of pure alveolar disease is pulmonary alveolar proteinosis, yet high resolution computed tomographic (HRCT) scanning has shown that, even in this entity, the interlobular and intralobular septa are thickened, forming the “crazy paving” pattern on thin-section CT.