Emphysema

Emphysema is the abnormal, permanent enlargement of air spaces distal to the terminal bronchioles, accompanied by destruction of alveolar walls, but without obvious fibrosis. Chronic obstructive pulmonary disease (COPD) is a spectrum of obstructive lung diseases that includes emphysema and chronic bronchitis – diseases that frequently coexist, especially in smokers. Emphysema is an extremely common disease and in most cases the diagnosis is established with clinical data including pulmonary function tests (PFTs). CT may be helpful for clarifying the diagnosis in mild cases or if another disease process (such as interstitial lung disease) is suspected. The three different types of emphysema (centrilobular, paraseptal, and panlobular) affect different parts of the secondary pulmonary lobule and are easily distinguished on CT. Emphysema distorts the normal lung anatomy and can cause superimposed processes (e.g. pneumonia or pulmonary edema) to look atypical on chest radiography and CT. Similarly, lung cancer may have an unusual morphology when it arises within emphysematous lung. Cystic lung disease and honeycombing in pulmonary fibrosis should not be confused with emphysema. Cysts and honeycombing have defined walls on CT, whereas centrilobular emphysema manifests as areas of low attenuation without perceptible walls.