A subcategory of chronic obstructive pulmonary disease. The disease is characterized by anatomic alterations of the lungs, such as the enlargement of airspaces and destruction of alveolar walls. [MeSH] Pathology.—Emphysema is characterized by permanently enlarged airspaces distal to the terminal bronchiole with destruction of alveolar walls (42,43). Absence of “obvious fibrosis” was historically regarded as an additional criterion (42), but the validity of that criterion has been questioned because some interstitial fibrosis may be present in emphysema secondary to cigarette smoking (56,57). Emphysema is usually classified in terms of the part of the acinus predominantly affected: proximal (centriacinar, more commonly termed centrilobular, emphysema), distal (paraseptal emphysema), or whole acinus (panacinar or, less commonly, panlobular emphysema). CT scans.—The CT appearance of emphysema consists of focal areas or regions of low attenuation, usually without visible walls (58). In the case of panacinar emphysema, decreased attenuation is more diffuse. (See also bullous emphysema, centrilobular emphysema, panacinar emphysema, paraseptal emphysema.) [Fleischner Society]

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