Pathology of Chronic Obstructive Pulmonary Disease: Diagnostic Features and Differential Diagnosis
Chronic obstructive pulmonary disease (COPD) is a general name for the chronic airflow obstruction that develops most often as a result of chronic tobacco smoking, but also after exposure to biomass fuels. The pathology of COPD encompasses a variety of pathologic lesions in the airways, lung parenchyma, and pulmonary vasculature, and these lesions can be correlated, to a greater or lesser degree, with changes in pulmonary function tests and clinical appearances. In general, although the mechanisms involved are complex, airflow obstruction can be attributed largely to a marked increase in airway resistance secondary to a variable mix of structural abnormalities involving all or many of the compartments of the airway. However, in individual cases, it may be difficult to prove associations between physiologic abnormalities and pathologic changes. The Global Initiative on Obstructive Lung Disease (GOLD), recently revised,1 classifies patients with COPD purely upon indices of airflow and thus far there is only limited integration with pathologic findings.
This chapter presents the pathologic features of COPD and how these findings can be differentiated from other lesions associated with airflow obstruction.
History of Pathologic Descriptions of Copd
The word emphysema is derived from Greek and means “to blow into,” hence “air-containing” or “inflated.” Although “voluminous lungs” and lungs “turgid particularly from air” were described respectively by Bonet in 16792 and Morgagni in 1769,3 the first description of enlarged airspaces in emphysema in the human, together with illustrations, was furnished by Ruysh in 1721,4 followed by Matthew Baillie in 1807, who not only clearly recognized and illustrated emphysema, but also pointed out its essentially destructive character.5,6
Laennec,7 writing in the early 1800s, made a number of seminal contributions to the basic descriptions of pathologic changes in COPD. He was the first to make a clear-cut distinction between interstitial emphysema and emphysema proper, and related the enlarged airspaces to the clinical syndrome of emphysema. He also recognized that air trapping and increased collateral ventilation were features of emphysematous lungs, and that the peripheral airways were the primary site of obstruction in emphysema. Furthermore, he noted that airspaces enlarged with increasing age, and he distinguished these changes from emphysema. He was the first to describe an association of emphysema with chronic bronchitis and to clearly describe the pathology of bronchiectasis.
Little of major importance was added to the gross descriptive morphology of emphysema for almost the next 150 years. The foundation of modern knowledge of the pathologic anatomy of pulmonary emphysema was laid by J. Gough in 19528 when he described centrilobular emphysema and distinguished it from panlobular emphysema. The paper section technique developed by Gough and Wentworth9 was largely responsible for this advance, as it made examinations of sections of entire inflated lungs ...