Respiratory bronchiolitis with fibrosis. High-resolution computed tomography findings and correlation with pathology

Recent pathology studies report that the lungs of cigarette smokers may demonstrate small localized subpleural foci of interstitial fibrosis associated with emphysema. Pathologically, this lesion has been termed smoking-related interstitial fibrosis, respiratory bronchiolitis-interstitial lung disease (ILD) with fibrosis, or airspace enlargement with fibrosis, but it is commonly misinterpreted on imaging and biopsy as a diffuse fibrosing interstitial pneumonia. The high-resolution computed tomography (HRCT) appearance of this process has not been defined.

We describe HRCT imaging of seven patients with this lesion present histologically.

HRCT features consisted of patchy areas of mild reticulation around predominantly subpleural upper/mid zone emphysematous changes in all cases, with variable patchy ground-glass change in six cases. Pathologically, there were distinctly circumscribed foci of dense, often hyalinized, interstitial fibrosis mixed with emphysema; variable numbers of smoker's macrophages were present in the airspaces. The fibrosis was confined to the subpleural regions. Three patients with follow-up information were clinically stable.

These data suggest that a CT pattern of patchy areas of reticular changes about predominantly upper zone emphysematous spaces may be seen in smokers who do not have clinical evidence of a diffuse ILD. We propose that this lesion be called respiratory bronchiolitis with fibrosis (RBF) to avoid confusion with other forms of ILD. RBF probably accounts for some of the cases of ILD seen in large radiologic surveys of smokers. The pathology literature indicates that RBF either has no functional effects or at worst represents mild, usually nonprogressive disease, and hence separation from other, more serious, forms of ILD is important. Recognition of this lesion on imaging may obviate the need for lung biopsy.