[CT findings of hypersensitivity pneumonitis]

CT findings of 22 cases of hypersensitivity pneumonitis (HP) were evaluated on 1 cm slices. All cases were diagnosed by transbronchial lung biopsy and clinical information. The study population included 8 men and 14 women with a mean age of 43 years. The causative antigens were considered to be so-called summer type in 17 cases, air humidifier in 1, pigeon in 1 and paint spray (isocyanate was suspected) in 3. CT examination were performed at a mean of 1.5 weeks after admission. In conclusion, characteristic CT findings of HP include combination of small nodular shadows and slight elevation of lung density. The size of nodular shadows was usually within 1 cm diameter, and their distribution was considered to be a centrilobular pattern, representing alveolitis and granuloma formation in a secondary lobule. It was though that the slight elevation of lung density developed when the disease extended all over the secondary lobule and the nodules developed when the disease was limited to the centrilobular lesion. In most cases, significant changes in proximal bronchi and pulmonary vasculatures could not be detected. The presence of segmental or lobar distribution of the shadows was also suggested. In addition to the typical findings, various other findings were also revealed; irregular shaped dense shadows, subpleural curvilinear shadow and honeycombing formation, especially in chronic cases. These findings have caused some difficulty in distinguishing HP from other interstitial diseases. More precise information can probably be obtained by thin slice CT than by 1 cm slice thicknesses, nevertheless, the standard method of CT should yield a useful diagnostic imaging.