Bronchiolar disorders: classification and diagnostic approach.

Bronchiolitis is a process in which inflammatory cells and mesenchymal tissue are both present, mainly centered in and around membranous and/or respiratory bronchioles, with sparing of a considerable portion of the other parenchymal structures. The distribution and amounts of the cellular and mesenchymal components vary from case to case, which accounts for the variety of histopathologic, radiographic, and clinical aspects of bronchiolitis. The clinical classification of bronchiolar diseases considers the causes or the clinical settings in which bronchiolitis develops: inhalation of toxic fumes, irritant gases or organic dusts, infectious and postinfectious bronchiolitis, collagen-vascular disease-associated bronchiolitis, posttransplant bronchiolitis, or rarer associations. A morphological classification based on histologic characteristics takes into account four main histologic patterns: cellular bronchiolitis, bronchiolitis with inflammatory/intraluminal polyps, constrictive or cicatritial bronchiolitis, peribronchiolar fibrosis, and bronchiolar metaplasia. High-resolution computed tomographic scanning (HRCT) is currently the best imaging technique for the evaluation of patients suspected of having bronchiolitis. HRCT findings in bronchiolar diseases with a good correlation with histopathologic changes are classified as follows: centrilobular tubular branching or nodular opacities; ground-glass attenuation or consolidation; mosaic perfusion; a mixed pattern. This article presents and briefly discusses the diagnostic approach to these diseases.