Chronic bronchiolitis

**Definition:** Bronchiolitis and bronchiolitis obliterans are general terms used to describe a nonspecific inflammatory injury that primarily affects the small airways and generally spares the interstitium. Bronchiolitis may be caused by inhalation injury, infection, or drugs; associated with organ transplantation or connective tissue disease; or may be idiopathic. The main pathologic categories of bronchiolitis are: constrictive, proliferative, follicular, airway-centred interstitial fibrosis, and diffuse panbronchiolitis. The constrictive and proliferative patterns may occur together.