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Learning Objectives
The student will be able to define emphysema and chronic bronchitis and differentiate their various forms, including etiology, pathogenesis, gross and microscopic morphology, and clinical presentation.
The student will be able to describe the histological presentation of asthma, particularly as it may involve both airways and lung parenchyma.
The student will be able to describe the development and appearance of bronchiectasis as it evolves from an initial obstructive process.
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Obstructive lung diseases are characterized by reductions in airflow due to increased resistance from partial or complete airway obstructions at any level. Such obstructions can arise from direct narrowing of the airway lumen or by decreased elastic recoil of the pulmonary parenchyma surrounding the airways, which has the effect of reducing lumen caliber. The many causes of obstructive disease include tumors, aspirated foreign bodies, asthma, emphysema, chronic bronchitis, cystic fibrosis, and bronchiolitis. This chapter will focus on the pathology of emphysema, chronic bronchitis, asthma, and bronchiectasis. Bronchiectasis is included here although it occurs as a result of airway obstruction, rather than being a cause in itself. The chronic obstructive pulmonary diseases (COPDs) comprise emphysema and chronic bronchitis. Though it is possible to have emphysema without chronic bronchitis or the converse, most patients have some degree of both, though one may dominate the clinical scenario. They share common etiologies, the most significant of which is tobacco smoking. Despite this significant association, most smokers do not develop COPD.
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PATHOLOGY OF EMPHYSEMA
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Emphysema is defined morphologically as the irreversible enlargement of airspaces distal to the terminal bronchioles, due to destruction of airspace walls and without obvious fibrosis. Emphysema is present in approximately one-half of adults at autopsy, most of whom were asymptomatic. Emphysema is further subdivided into four subtypes based on the anatomic distribution of the airspace enlargement: centriacinar (centrilobular), panacinar (panlobular), distal acinar (paraseptal), and irregular.
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Centriacinar emphysema (Figs. 20.1 and 20.2) is characterized by airspace enlargement at the level of the respiratory bronchioles, sparing the distal alveoli. Anatomically, the several acini that comprise a lobule (Chap. 2) are arranged such that their respiratory bronchioles are grouped in the center of the lobule. This anatomic arrangement underlies the alternate name, centrilobular emphysema. Centriacinar emphysema accounts for more than 95% of those cases of emphysema with clinically significant airway obstruction. It is more pronounced in the upper lobes and is the type of emphysema most strongly associated with smoking.
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