Obstructive pneumonitis: a pathologic and pathogenetic reappraisal.

It is widely accepted that pneumonitis distal to an obstructing airway tumor is the result of infection. The authors performed a prospective study to reevaluate this concept and to clarify the nature of the pathologic findings underlying the observed radiographic changes. Specimens were examined for 50 consecutive patients undergoing resection of pulmonary carcinoma. Histologic changes interpreted as noninfectious were found in 42 cases. Findings suggestive of recent or remote infection were also present in nine of these 42 specimens and were localized predominantly in relation to small- to medium-sized airways (acute bronchitis or bronchiolitis); these changes were always present in a background of noninfectious pneumonitis. The authors conclude that the radiographic changes seen in airway obstruction in surgically excised lungs are usually due to consolidation of lung parenchyma by a noninfectious process. When infection does occur, it involves primarily the airways and is not likely to be radiographically detectable.