Clinical assessment of airway remodeling in asthma - Utility of computed tomography

Airway remodeling is an established feature of asthma. Histologic examination is essential in the assessment of remodeling that is a pathologic concept. Examinations of autopsied or resected lung have enabled detailed morphologic and morphometric studies and have provided fundamental knowledge of airway remodeling in asthma. However, such materials are only accidentally available, and clinical information may often be insufficient in autopsied cases. Bronchoscopic mucosal biopsy has been widely used since the 1980s, and has contributed substantially to basic investigations of inflammation and remodeling. However such specimens are limited in size and depth, limited to central airways, and the procedure might be too invasive to be repeated. Remodeling can also be assessed indirectly. Pulmonary function tests to evaluate chronic airflow obstruction are available in clinical settings and suitable for screening or mass studies, but they may be affected by concomitant diseases or short-term asthma control. Computed tomography (CT) has recently been utilized to assess remodeling. It cannot discern pathologic details but provides a broader range of airway/lung morphology and may be less invasive compared to biopsy. In addition to classic subjective evaluations, quantitative assessment has been reported for central airway dimensions, such as airway wall area, luminal area and wall thickness, and for peripheral airway abnormality or air trapping as measured by decreased lung attenuation or increased mosaic perfusion. This article summarizes the merits and limitations of various methods to assess airway remodeling, and describes the details of methodologies, interpretations, pathophysiologic relevance, and future directions of asthmatic airway remodeling assessed by CT.