Bronchiolitis obliterans

Bronchiolitis obliterans (BO) is a fibrotic lung disease involving the smal l conducting airways. BO may be classified by etiology and underlying disea se or, more commonly, by histopathological pattern. The two major histopath ological categories are (1) BO organizing pneumonia (BOOP) and proliferativ e bronchiolitis and (2) constrictive bronchiolitis. The former is often idi opathic in nature and may also be associated with connective tissue disease s and inhalation injury Characteristic findings on chest imaging include al veolar infiltrates and ground glass opacities and pulmonary function tests (PFTs) usually reveal restrictive dysfunction. Constrictive bronchiolitis i s associated with organ transplantation, infections, connective tissue dise ases, inhalation injury, and drugs and may also have an idiopathic origin. The radiographic characteristic is a mosaic pattern on high-resolution comp uted tomography (HRCT) and PFTs most often reveal obstructive dysfunction. This article will attempt to review constrictive BO, including histopatholo gy, clinical presentation, radiographic appearance, and physiological findi ngs, for both idiopathic diseases, as well as specific clinical-associated entities.