Emphysema

Pulmonary emphysema is defined in morphological rather than clinical terms. The 1958 Ciba Symposium defined emphysema as an "increase beyond the normal of air spaces, distal to the terminal bronchiole, either from dilation or from destruction of their walls." The subsequent American Thoracic Society statement in 1962 made anatomic destruction a part of the definition: "Emphysema is an anatomic alteration of the lung characterized by an abnormal enlargement of the air spaces distal to the terminal, nonrespiratory bronchiole, accompanied by destructive changes of the alveolar walls."

The definition was refined in 1985 in a workshop report of the National Heart, Lung, and Blood Institute: "Emphysema is defined as a condition of the lung characterized by abnormal, permanent enlargement of airspaces distal to the terminal bronchiole, accompanied by the destruction of their walls, and without obvious fibrosis."

Emphysema can also be subclassified in anatomic terms. The acinus is the gas-exchanging unit of the lung served by a single terminal bronchiole. Within the acinus, the terminal bronchiole is succeeded by three orders of branching respiratory bronchioles that are subsequently succeeded by alveolar ducts and terminal alveolar sacs, all of which bear alveoli. If emphysematous changes predominate in the region of respiratory bronchioles, the condition is termed centriacinar or centrilobular emphysema. More uniform involvement constitutes panacinar or panlobularemphysema. Emphysema located predominantly in the periphery of the acinus along lobular septa isparaseptal emphysema. Occasionally, emphysema may occur adjacent to a scar or fibrotic process and is called paracicatricial emphysema.

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