In: Bronchiolitis7 Apr 2014
Imaging studies have had a limited role in the detection of BO developing after lung transplantation. Bronchiectasis has been described as an associated finding on both radiographs and CT;’ however, radiologic detection of bronchial dilatation infrequently precedes the clinical diagnosis of BOS. Bronchiectasis may also result as sequelae of previous infections. In our series, bronchiectasis had a sensitivity of 36%, specificity of 80%, and accuracy of 57% for the identification of BO. One of two patients who had bronchiectasis identified on HRCT but without BO had had documented episodes of bronchiolitis obliterans organizing pneumonia and cytomegalovirus pneumonia in the first postoperative year. A mosaic pattern of lung attenuation was identified in 38% of our study patients with a sensitivity of 64%, specificity of 90%, and accuracy of 70% for BO. On HRCT images taken in inspiration, the mosaic pattern of lung attenuation in BO represents regions of normal lung interspersed among regions of diseased and obstructed lung that are unable to empty their air content on expiration. In the regions of air trapping, manifest as the areas of lower attenuation, a decrease in the number and size of pulmonary vessels can often be appreciated and likely results from physiologic shunting of blood away from poorly ventilated regions.
After an expiratory maneuver, the attenuation differences between normal and obstructed lung units are rendered more conspicuous as the normal lung units contract in volume and increase in attenuation while obstructed lung units retain both their volume and low attenuation. Air trapping on expiratory HRCT has been described previously in a number of obstructive lung diseases resulting from bronchial obstruction and narrowing’ or decreased lung compliance. Air trapping, though more limited in extent, has also been shown in normal volunteers.
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