AIR TRAPPING ON EXPIRATORY HIGH-RESOLUTION CT SCANS IN THE ABSENCE OFINSPIRATORY SCAN ABNORMALITIES - CORRELATION WITH PULMONARY-FUNCTION TESTS AND DIFFERENTIAL-DIAGNOSIS

OBJECTIVE. We wish to describe the differential diagnosis and pulmonar y function correlates of patients with normal findings on inspiratory high-resolution CT (HRCT) scans who showed air trapping on expiratory scans. MATERIALS AND METHODS. HRCT scans in 273 consecutive patients w ith suspected diffuse lung disease were reviewed. HRCT consisted of in spiratory scans at 1- to 2-cm intervals and expiratory scans at three levels. Studies considered to show expiratory air trapping were divide d into two groups, one having normal findings on inspiratory scans and one having abnormal findings on inspiratory scans. Pulmonary function test results in these groups were compared with a group of patients w ho had normal findings on inspiratory and expiratory HRCT scans. RESUL TS. Forty-five patients showed air trapping on expiratory HRCT scans. Of these 45 patients, inspiratory high-resolution CT scans showed abno rmal findings in 36 (bronchiectasis, bronchiolitis obliterans, asthma, chronic bronchitis, and cystic fibrosis). In the remaining nine patie nts, inspiratory HRCT had normal findings; conditions in these nine pa tients included bronchiolitis obliterans (ia = 5), asthma (n = 3), and chronic bronchitis (il = 1). Results of pulmonary function tests in p atients with air trapping and normal findings on inspiratory scans wer e intermediate, falling between those of patients with normal findings on inspiratory and expiratory HRCT scans and those of patients with a ir trapping and abnormal findings on inspiratory scans. CONCLUSION. Ai r trapping on expiratory HRCT scans in patients with normal findings o n inspiratory scans is most often associated with bronchiolitis oblite rans and asthma. Obtaining expiratory scans in patients who may have o ne of these diseases is recommended.