[CT pathologic correlative study of bronchiolitis obliterans organizing pneumonia]

Though bronchiolitis obliterans organizing pneumonia (BOOP) was proposed as a new infiltrative lung disease in 1985, we think it has two radiologic problems. First, in spite of interstitial pneumonia, about half of chest radiographs of BOOP has been reported to show alveolar opacities. Second, because radiologic features of both some cases of BOOP and of usual interstitial pneumonia (UIP) show reticular shadows on chest radiographs, it is sometimes difficult to differentiate between two diseases. We correlated CT images with open lung biopsy specimens and evaluated CT's ability to differentiate BOOP from UIP. CT findings of all cases of BOOP were: (1) markedly increased dense infiltrates of various sizes which demarcated sharply from normal lung field. Air bronchogram was always present. (2) less dense images were seen which also stood out against the normal lung field. The former corresponded to air space consolidation formed by organized exudates and inflammatory cells within alveolar ducts and alveoli, while the latter indicated luminal and mural alveolitis. Both findings were sharply delineated from each other probably because of intervening interlobular septa. Conglomerated small cystic shadows and air bronchography within areas of intense lung density were seen in CT images of most of 28 patients with UIP. Those findings proved to correspond to macroscopic or microscopic honey combing which were not seen in our cases of BOOP. These radiologic and pathologic features of UIP were different.