Computed Tomography of the Pulmonary Parenchyma: CT in the Evaluation of Diffuse Pulmonary Pathology
The Persistent Pulmonary Infiltrate: A focal infiltrate that persists despite presumably effective therapy is a common clinical problem. Excluding the possibility of a proximal obstructive lesion is an essential step in the management of such cases. CT is well suited to such a task as an adjunct to bronchoscopy, which may be hampered by the presence of associated inflammation. Of paramount importance in these cases is the use of IV contrast agents and thin, 4- to 5-mm contiguous sections throughout the hila. Bronchiectasis as a cause of persistent infiltrate or as a primary clinical issue can be accurately staged with CT, and even minor degrees of the disease can be accurately staged with thin-section CT.
CT in the Evaluation of Diffuse Pulmonary Pathology
The exact place of CT in the investigation of diffuse lung disease is still being actively evaluated. Plain radiography remains the standard for detection and characterization of disease. CT has the unique advantage of offering an unobstructed cross-sectional view of lung anatomy. In addition, the introduction of optimized CT techniques based on the use of very thin sections in a high-resolution mode (HRCT) has all but eliminated the problem of superimposition of structures inherent to conventional radiography. A body of work now exists that attempts to establish the interpretational bases of pulmonary parenchymal HRCT and validate its use. Most of the early efforts have been centered on optimizing the technique and defining the basic CT signs of diffuse lung pathology with anatomopathologic correlations. itat on
Basic HRCT Signs
Correlations with either inflated lung specimens or Gough sections indicate that the basic lobular anatomy of the lung can be recognized with HRCT. Resolution of structures in the order of 100 to 200 |x has been reported. Secondary interlobular septa are readily visualized at the periphery of the lung. Differentiating features of airspace vs interstitial disease have been defined, keeping in mind that such a division is arbitrary in that most pathologic processes combine both.