Fibrosing Bronchiolitis Evolving from Infectious or Inhalational Acute Bronchiolitis. A Reversible Lesion.

Rationale: Occasional cases of bronchiolitis show pathologic features somewhat suggestive of constrictive bronchiolitis, but with granulation tissue plugs that variably occlude the lumen in a pattern more typical of organizing pneumonia. These cases are poorly defined in the literature and the course of patients with this pattern of disease is unclear.

Objective: To describe an uncommon and potentially treatable pattern of acute bronchiolitis that has been termed fibrosing bronchiolitis.

Main Results: We report three patients with respiratory failure and acute onset of probable infectious or inhalational bronchiolitis that was characterized by centrilobular nodules and a variable tree-in-bud appearance on computed tomography. All patients showed an uncommon pattern of bronchiolitis on surgical lung biopsy. The pathologic abnormalities were confined to the bronchioles and consisted of reepithelialized, partially collagenized and variably polypoid plugs of granulation tissue that narrowed the bronchiolar lumens. All three patients improved dramatically on immunosuppressive therapy.

Conclusions: These cases of fibrosing bronchiolitis represent an uncommon pattern of acute bronchiolitis that is reversible if detected at an early stage. Early recognition and treatment may prevent development of permanent bronchiolar fibrosis.