High-resolution CT of alveolar filling disorders.

Airspace filling process is characterized on CT by the presence of one or more fairly homogeneous areas of consolidation with little or no volume loss. The consolidation may be segmental, subsegmental, lobular, or acinar (10 mm or less in diameter). Poorly defined centrilobular nodules may be associated. The margin of the consolidation usually is poorly defined except in the areas in which the consolidation abuts the pleura. Air-containing bronchi or bronchioles (CT air bronchograms or air bronchiolograms) are seen frequently. Many diseases can present with alveolar filling disorders. Because the HRCT findings overlap among various alveolar filling disorders, it may be impossible to make a definite diagnosis with HRCT findings alone. Integration of HRCT findings including disease pattern and distribution and time factors including evolution and resolution of the disease, however, may enable to narrow differential diagnosis of alveolar filling diseases. Furthermore, clinical and laboratory findings also may provide helpful clues to reach a reasonable diagnosis. The role of HRCT in alveolar filling disorders is not limited to diagnosis. HRCT also plays a useful role in determining the extent of disease and in identifying accompanying abnormalities, and complications of the primary disease.