Chronic obliterative bronchiolitis

**Definition:** Bronchiolitis obliterans is commonly used to describe a number of unrelated conditions whose common end point is functional obstruction of bronchioles. A typical form is constrictive bronchiolitis. Constrictive bronchiolitis is an uncommon histologic finding characterised by alterations in the walls of membranous and respiratory bronchioles, often without extensive changes in alveolar ducts and alveolar walls. These changes lead to concentric narrowing or complete obliteration of the airway lumen. The clinical manifestations of constrictive bronchiolitis usually include progressive airflow obstruction, sometimes in the presence of a relatively normal chest radiograph. The clinical severity depends upon the type, extent, and severity of the initial lung injury.

**Exclusions:** - Respiratory conditions due to inhalation of chemicals, gases, fumes or vapours