Bronchiolitis obliterans.

Bronchiolitis obliterans (BO) is a fibrotic lung disease involving the small conducting airways. BO may be classified by etiology and underlying disease or, more commonly, by histopathological pattern. The two major histopathological categories are (1) BO organizing pneumonia (BOOP) and proliferative bronchiolitis and (2) constrictive bronchiolitis. The former is often idiopathic in nature and may also be associated with connective tissue diseases and inhalation injury. Characteristic findings on chest imaging include alveolar infiltrates and ground glass opacities and pulmonary function tests (PFTs) usually reveal restrictive dysfunction. Constrictive bronchiolitis is associated with organ transplantation, infections, connective tissue diseases, inhalation injury, and drugs and may also have an idiopathic origin. The radiographic characteristic is a mosaic pattern on high-resolution computed tomography (HRCT) and PFTs most often reveal obstructive dysfunction. This article will attempt to review constrictive BO, including histopathology, clinical presentation, radiographic appearance, and physiological findings, for both idiopathic diseases, as well as specific clinical-associated entities.