[Pathologic anatomy of bronchiolitis with the exclusion of acute forms]

ANATOMIC DEFINITION: Bronchiolitis is an inflammatory condition of the small airways, membranous and respiratory bronchioles.

The lesions result from exogenous or endogenous aggression of the epithelium. The inflammatory reactions caused by this aggression may regress spontaneously or after treatment or may progress to fibrosis.

Obliterating bronchiolitis is the best understood form. There are two types: polypoid obliterating bronchiolitis and constrictive bronchiolitis. This latter form is the only one which causes an obstructive syndrome. Other histological forms have been described.

Certain lesions have particular morphological features allowing their identification (smokers bronchiolitis, follicular bronchiolitis, diffuse panbronchiolitis) and others occur in classical associations (rheumatoid polyarthritis, chronic lung graft rejection). In many cases however, the lesions are relatively monomorphous and result from many different causes. Rigorous comparison between pathological findings and the clinical presentation is needed to classify these types and integrate them into a particular context.