Computed Tomography of the Pulmonary Parenchyma: Disease Specific Applications
The last category of signs described in interstitial disease is that of ill-defined patches of increased parenchymal density with a ground-glass appearance that correlate pathologically with diffuse thickening of the interstitium with obliteration of airspaces.
Various combinations of the above described basic signs have been reported in specific disease entities such as fibrosing alveolitis. Preliminary work suggestive of an enhanced differential diagnostic capability between entities such as bronchiolitis obliterans and usual interstitial pneumonia has also been described.
Disease Specific Applications
Pulmonary Emphysema: Pulmonary emphysema has been the subject of intensive CT studies. The destructive changes of emphysema can be exquisitely recognized with HRCT techniques. The most interesting prospect of such studies is the potential for more accurately quantifying the extent of pulmonary damage. A high correlation can be found between pathologic and HRCT-derived visual scores of centri-lobular emphysema. Using image analysis techniques, the extent of destruction can be more precisely quantified. Such computational intensive methods now readily accessible offer the possibility of quantifying gas and tissue volumes and can serve as an adjunct to more conventional physiologic measurements.
Positive correlations with volumetric parameters of pulmonary function tests (PFTs) have also been demonstrated, and ongoing studies are addressing the potential of using CT in further refining assessments of lung function. Clinically, CT has found some use in selecting patients for resection of bullous disease when PFTs are ambiguous. More info
Pneumoconioses: Very early, many realized that the clear visualization of pleural surfaces afforded by CT would lead to better detection of the pleural manifestations of asbestos exposure. More recently, the advent of HRCT has opened the prospect of more accurate assessment of parenchymal asbestosis. Efforts to define and validate the basic signs of asbestosis are under way. These efforts are hampered by the understable lack of a “gold standard” correlative data set and by the known overlap between fibrotic changes due to asbestosis and those due to other etiologies. There is great interest in further evaluating the ability of HRCT in more reliably detecting and classifying pneumoconioses as the current semiquantitative ILO classification suffers from methodologic limitations related to frequent interobserver and intraobserver interpretive errors. For example, the problems of false negative as well as false positive plain film estimations of the presence and grading of pneumoconioses are well recognized.^ Attempts at correlating PFTs with CT findings in the assessment of asbestosis and silicosis have also been reported. Classification of silicosis using CT has also been suggested.