ABSTRACT
Bronchiolitis is a nonspecific term that denotes the presence of inflammation and/or fibrosis in the bronchioles (i.e., small airways with an internal diameter of 2 mm or less). Radiologic and histopathologic findings suggestive of bronchiolitis are encountered often, and the significance of identifying such abnormality varies according to the clinical context. Bronchiolitis may represent the primary disease process (then referred to as primary bronchiolitis) or may be a minor component in the context of another disorder that is primarily centered at larger airways (e.g., bronchiectasis) or the pulmonary parenchyma (e.g., organizing pneumonia). Several classification schemes for primary bronchiolar disorders have been proposed, but none has been universally adopted. Histopathologic subtypes of bronchiolitis can be broadly divided into (1) constrictive bronchiolitis (synonymous with obliterative bronchiolitis), which is characterized by the presence of peribronchiolar and submucosal fibrosis; and (2) cellular bronchiolitis, in which inflammatory cells can be identified within and around the bronchioles. Cellular bronchiolitides are respiratory bronchiolitis, acute bronchiolitis, follicular bronchiolitis, diffuse panbronchiolitis, and diffuse aspiration bronchiolitis, in addition to other miscellaneous forms. Each of the histopathologic subtypes can be encountered in association with a variety of disorders and/or exposures. Individuals with bronchiolitis commonly manifest nonspecific respiratory symptoms (e.g., cough, dyspnea), and may or may not exhibit abnormalities on pulmonary function tests. Chest radiography is frequently normal, and chest CT is the gold-standard imaging modality whenever bronchiolitis is suspected. In the appropriate clinical context, a chest CT study consistent with bronchiolitis may be sufficiently diagnostic. Nevertheless, there are situations wherein obtaining lung tissue specimens is necessary not only to establish a diagnosis of bronchiolitis, but also to identify its subtype. Management of all patients with bronchiolitis should include: (1) identifying and managing the underlying cause or disease; (2) adequate control of potentially exacerbating conditions (e.g., smoking, aspiration); and (3) providing the optimal supportive care (e.g., smoking cessation, bronchodilators, supplemental oxygen, vaccinations). Certain bronchiolitis subtypes may be amenable to specific treatments, such as the use of macrolide antibiotics in individuals with bronchiolitis obliterans syndrome and diffuse panbronchiolitis. Prognosis varies according to the bronchiolitis subtype, and the clinical context in which it is encountered.
