Seminars in respiratory and critical care medicine vol:24 issue:5 pages:473-88
Small airways disease (SAD) is defined as a pathologic condition in which the small conducting airways are affected either primarily or as part of other pulmonary changes. Diagnosis is often difficult because the many histopathologic subtypes that have been described often lack obvious clinical or imaging correlates and because widespread involvement is needed before clinical symptoms and abnormalities on pulmonary function testing occur. High-resolution computed tomography (HRCT) can be helpful to detect, characterize, and quantify small airways involvement. These airways may become visible directly when inflammation of the bronchiolar wall and accompanying exudates develop. Obstruction of the small airways may be detected indirectly by HRCT when it causes regional underventilation resulting in reduced perfusion. This article discusses the direct and indirect HRCT signs of small airways involvement and, based on the fundamental differences between these signs, gives a short review of the HRCT features of the most important diseases that can affect the small airways.