Emphysema classification

Overview
Emphysema is a long-term, progressive disease of the lungs that primarily causes shortness of breath. In people with emphysema, the tissues necessary to support the physical shape and function of the lungs are destroyed. It is included in a group of diseases called chronic obstructive pulmonary disease or COPD (pulmonary refers to the lungs). Emphysema is called an obstructive lung disease because the destruction of lung tissue around smaller sacs, called alveoli, makes these air sacs unable to hold their functional shape upon exhalation. Emphysema is most often caused by tobacco smoking and long-term exposure to air pollution. The term emphysema means "swelling" and derives from the Greek ἐμφυσᾶν emphysan meaning "inflate" - itself composed of ἐν en, meaning "in", and φυσᾶν physan, meaning "breath, blast".

Classification
Emphysema can be classified into primary and secondary types. However, it is more commonly classified by location into panacinary and centroacinary (or panacinar and centriacinar, or centrilobular and panlobular).


 * Panacinar (or panlobular) emphysema: The entire respiratory acinus, from respiratory bronchiole to alveoli, is expanded. Occurs more commonly in the lower lobes (especially basal segments) and in the anterior margins of the lungs.
 * Centriacinar (or centrilobular) emphysema: The respiratory bronchiole (proximal and central part of the acinus) is expanded. The distal acinus or alveoli are unchanged. Occurs more commonly in the upper lobes.

Other types include distal acinar emphysema and irregular emphysema. A special type is  congenital lobar emphysema  (or CLE).

Congenital lobar emphysema


CLE results in overexpansion of a pulmonary lobe, and resultant compression of the remaining lobes of the ipsilateral lung (and possibly also the contralateral lung). There is bronchial narrowing because of weakened or absent bronchial cartilage. There may be congenital extrinsic compression, commonly by an abnormally large pulmonary artery. This causes malformation of bronchial cartilage, making them soft and collapsible. CLE is a potentially reversible (yet possibly life-threatening) cause of respiratory distress in the neonate.

Paraseptal emphysema
Paraseptal emphysema is a type of emphysema which involves the alveolar ducts and sacs at the lung periphery. The emphysematous areas are subpleural in location and often surrounded by interlobular septa (hence the name). It may be an incidental finding in young adults, and may be associated with spontaneous pneumothorax. It may also be seen in older patients with centrilobular emphysema. Both centrilobular and paraseptal emphysema may progress to bullous emphysema. A bulla is defined as being at least 1 cm in diameter, and with a wall less than 1mm thick. Bullae are thought to arise by air trapping in emphysematous spaces, causing local expansion.