EMPHYSEMA - DEFINITION, IMAGING, AND QUANTIFICATION

This review will discuss imaging of the chest in patients with pulmona ry 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 consequence s and then review the imaging findings, with emphasis on CT, in patien ts with this disease. The more severe the morphologic emphysema, the m ore likely a radiographic diagnosis will be made, no matter what crite ria are used. The criterion of arterial deficiency is specific but ins ensitive. The criteria used to assess overinflation are sensitive but not specific. CT can be used for both qualitative and quantitative ass essment of emphysema. The presence and extent of emphysema can be dete rmined by visual assessment of areas of abnormally low attenuation or by objective quantification based on the attenuation values. Statistic ally significant correlations between emphysema and CT findings have b een shown in numerous studies, but mild morphologic emphysema may be m issed by CT, and occasionally CT scans give false-positive findings. I n patients with moderate to severe emphysema, the severity of emphysem a is underestimated on the basis of CT findings by a factor of approxi mately three when compared directly with results of pathologic examina tion of lung specimens. In spite of these limitations, CT is the best way of recognizing emphysema in living patients and probably has a sig nificant role in recognizing localized emphysema that is amenable to s urgical treatment.