Abstract

Small airway diseases are seen in many clinical conditions. The locations of small airway diseases are small bronchioles including terminal and respiratory bronchioles, and alveolar duct. The histopathologic features of bronchiolar injury have been described variously and have led to confusing and overlapping terms. The purpose of this article is to describe the clinical characteristics and histopathologic interpretation of small airway diseases. We classify the small airway diseases as primary bronchiolar diseases, and secondary bronchiolar diseases including pulmonary parenchymal diseases, and large airway diseases with prominent bronchiolar involvement. Primary bronchiolar diseases include respiratory bronchiolitis, acute bronchiolitis, constrictive bronchiolitis, follicular bronchiolitis, diffuse panbronchiolitis, mineral dust airway diseases, and a few other variants. Pulmonary parenchymal diseases with bronchiolar involvement include respiratory bronchiolitis-associated interstitial lung disease, organizing pneumonia, hypersensitivity pneumonitis, pulmonary Langerhans' cell histiocytosis, sarcoidosis and idiopathic pulmonary fibrosis. Bronchiolar changes can also be seen in large airway diseases such as chronic bronchitis, bronchiectasis, cystic fibrosis and asthma. The patterns of bronchiolar response to various injuries are relatively limited and these patterns are generally non-specific in regard to the etiology. Appropriate interpretation and diagnosis of small airway diseases depend on judicious correlation of clinical, radiologic, and histopathologic characteristics.

• Keywords: Small airway disease;Primary bronchiolar disease;Secondary bronchiolar disease;Tobacco-related disease;