Bronchiolitis, an update.

Besides the classical forms of acute and chronic bronchiolitis, different special forms, such as obliterative, respiratory, and follicular bronchiolitis are recognized. In addition, even new entities emerge, such as Sauropus-induced bronchiolitis. Despite this progress in pathology, pulmonologists still prefer the diagnostic term 'small airways disease', instead of the more specific and even etiology-directed diagnoses provided by the morphologic examination. In this overview, an updated classification will be presented, which includes all forms of bronchiolitis described so far. This classification is structured along morphologic features of bronchiolitis. Different forms of acute and chronic bronchiolitis are described, so that a given reaction pattern can be associated with specific causes, such as eosinophilic bronchiolitis in asthma, or necrotizing bronchiolitis in viral infection. However, there exist more than just one morphologic reaction for a given etiologic agent, resulting in an overlap of morphologic appearances for a given disease.