Acute interstitial pneumonia

Low power photomicrograph shows dramatic interstitial thickening in a patient with acute interstitial pneumonia (Hamman-Rich disease). The prominent air spaces represent alveolar ducts while the intervening lung shows collapsed alveolar septa distorted by proliferating fibroblasts and myofibroblasts.

Low-power photomicrograph of normal lung tissue shows open alveoli with thin, capillary-containing interstitial spaces. An artery (A) is identifiable by its thick, muscular wall; the accompanying bronchus (B) contains mucoid material and is lined by columnar respiratory epithelial cells.