Differential diagnosis of chronic diffuse infiltrative lung disease on high-resolution computed tomography

Abstract

ANY CHRONIC lung diseases are characterized by diffuse infiltration of the lung parenchyma. Because most of these diseases involve both the interstitium and alveolar spaces, the term chronic infiltrative lung disease is preferable to chronic interstitial lung disease. ~ The limited contrast resolution and projectional nature of the chest radiograph results in considerable limitations in the detection and characterization of diffuse infiltrative lung disease. At least 10% of patients with biopsy-proven diffuse lung disease have a normal radiographic appearance. 2 Even when evaluated by experienced radiologists, radiographic findings are frequently nonspecific. In a review of the radiographic findings in 365 patients with diffuse infiltrative lung disease, McLoud et al L included the correct diagnosis in the first 2 radiologic choices in only 50% of cases. Since its introduction in 1985, high-resolution computed tomography (HRCT) has revolutionized the investigation of patients with suspected diffuse infiltrative lung disease. HRCT may show clinically suspected disease not apparent on the chest radiograph and has a higher specificity than the radiograph in excluding parenchymal abnormalities. Several studies have shown that HRCT also allows a substantially greater accuracy than the radiograph in the differential diagnosis of infiltrative lung diseases. The differential diagnosis of chronic diffuse infiltrative lung diseases is based on the pattern and distribution of findings (Table 1). The HRCT features of chronic infiltrative lung disease include interlobular septal thickening, irregular linear opacities, cystic airspaces, small nodules, groundglass pattern, and air-space consolidation. INTERLOBULAR SEPTAL THICKENING (SEPTAL PATTERN)