Emphysema: definition, imaging, and quantification.

This review will discuss imaging of the chest in patients with pulmonary emphysema. Imaging findings must be related to the structure of the lung because emphysema is defined in anatomic terms. Accordingly, we first review the anatomic definitions of emphysema and its consequences and then review the imaging findings, with emphasis on CT, in patients with this disease. The more severe the morphologic emphysema, the more likely a radiographic diagnosis will be made, no matter what criteria are used. The criterion of arterial deficiency is specific but insensitive. The criteria used to assess overinflation are sensitive but not specific. CT can be used for both qualitative and quantitative assessment of emphysema. The presence and extent of emphysema can be determined by visual assessment of areas of abnormally low attenuation or by objective quantification based on the attenuation values. Statistically significant correlations between emphysema and CT findings have been shown in numerous studies, but mild morphologic emphysema may be missed by CT, and occasionally CT scans give false-positive findings. In patients with moderate to severe emphysema, the severity of emphysema is underestimated on the basis of CT findings by a factor of approximately three when compared directly with results of pathologic examination of lung specimens. In spite of these limitations, CT is the best way of recognizing emphysema in living patients and probably has a significant role in recognizing localized emphysema that is amenable to surgical treatment.