USMLE Answer 60

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60. The correct answer is D. There are two main morphologic forms of emphysema, centriacinar and panacinar. The panacinar variant is related to alpha1-antitrypsin deficiency; the entire acinus is enlarged, from the respiratory bronchiole to the distal alveoli.

Centriacinar emphysema (choice A) is characterized by enlargement of the central portions of the acinus, i.e., the respiratory bronchiole, and its pathogenesis is related to exposure to tobacco products and coal dust.

Interstitial emphysema (choice C) is not a true form of emphysema. It results from penetration of air into the pulmonary interstitium. This may occur when alveolar tears develop because of a combination of coughing and airway obstruction (e.g., children with whooping cough) or a chest wound that injures the underlying lung parenchyma (e.g., a fractured rib).

Compensatory emphysema (choice B) and paraseptal emphysema (choice E) are associated with scarring. Both are frequent but usually clinically silent. Paraseptal emphysema, however, may lead to spontaneous pneumothorax in young patients. In fact, this form is more severe in areas adjacent to the pleura, where large, cyst-like structures may develop and rupture into the pleural cavity.