Histology of childhood bronchiolitis obliterans

Childhood bronchiolitis obliterans (CBO) is an uncommon disease characterized by persistent signs and symptoms of obstructive respiratory disease after an acute bronchiolar injury. It is considered to be a complication of viral infection, most often of adenovirus, and is usually classified as a constrictive-type bronchiolitis obliterans (BO). Few reports have described its histology. We present the histopathological features of 34 pediatric patients with a diagnosis of BO, comprising 30 open lung biopsies (OLB), 2 lobectomies, and 2 autopsies. Quantitative analysis was performed on the OLB to better characterize the morphological changes observed in these lungs. Of 37 patients, 25 were male and 9 were female, ranging from 7 months to 15 years of age. Airway diameter in terminal bronchioles varied from 50-600 microm. Ninety-seven percent of the CBO were of constrictive type, with variable degrees of airway obstruction. Chronic inflammation in the bronchioles was mild in 63% of the patients. Aggregates of foamy macrophages, mucostasis, and bronchiectasis appeared in, respectively, 93%, 40%, and 30% of the biopsies. There was more hyperinflation than atelectasis (40.1% and 24.3%, respectively). Lobectomies and autopsies showed more severe bronchiolar obliteration, associated with bronchiectasis. The results show that CBO is characterized histologically mainly by a constrictive pattern, with variable degrees of inflammation and airway obliteration. Secondary signs of airway obstruction are invariably present. Mild histological changes may predominate and should be carefully evaluated by the pathologist.