A morphologic study of the airway structure abnormalities in patients with asthma by high-resolution computed tomography

Abstract

Background: Airway structure changes, termed as airway remodeling, are common in asthma patients due to chronic inflammation, which can be assessed by high-resolution computed tomography (HRCT). Considering the controversial conclusions in the correlation of morphologic abnormalities with clinical feature and outcome, we aimed to further specify and evaluate the structural abnormalities of Chinese asthmatics by HRCT.

Methods: From August 2012 to February 2015, outpatients with asthma were recruited consecutively in the Asthma Center of West China Hospital, Sichuan University. Standard HRCT and pulmonary function test (PFT) were performed to collect information of bronchial wall thickening, bronchial dilatation, mucus impaction, emphysema, mosaic perfusion, atelectasis, and spirometric parameters. We reported the incidence of each structural abnormality in HRCT and compared it among different asthmatic severities.

Results: A total of 123 asthmatics were enrolled, among which 84 (68.3%) were female and 39 (31.7%) were male. At least one structural abnormality was detected by HRCT in 85.4% asthmatics, and the incidence of bronchial wall thickening, bronchial dilatation, mucus impaction, emphysema, mosaic perfusion, and atelectasis was 57.7%, 51.2%, 22%, 24.4%, 5.7% and 1.6%, respectively. The incidences of bronchial wall thickening, bronchial dilation and emphysema were significantly increased by asthma severity (P<0.05), while incidences of mucus impaction (26/27, 96.30%), mosaic perfusion (6/7, 85.71%) and atelectasis (2/2, 100%) were mainly found in severe asthma. We found a longer asthma history (28.13±18.55 years, P<0.001, P=0.003), older age (51.30±10.70 years, P=0.022, P=0.006) and lower predicted percentage of forced expiratory volume in one second (FEV₁%) (41.97±15.19, P<0.001, P<0.001) and ratio of forced expiratory volume to forced vital capacity (FEV₁/FVC) (48.01±9.55, P<0.001, P<0.001) in patients with severe bronchial dilation compared with those in none and mild bronchial dilation. A negative correlation was also found between the extent of bronchial dilation and FEV₁% as well as FEV₁/FVC (r=-0.359, P=0.004; r=-0.266, P=0.035, respectively).

Conclusions: The incidences of structural abnormalities detected by HRCT are fairly high in Chinese asthma populations, especially the bronchial wall thickening and bronchial dilation, which are significantly increased in severe asthma, and are potential risk factors of pulmonary function decline in asthmatics.

Keywords: Bronchial asthma; airway remodeling; bronchiectasis; high-resolution computed tomography (HRCT).

Figure 1

Measurement of bronchial wall thickening in chest HRCT. HRCT manifestations of (A) normal bronchial wall (0.8 mm) from a patient with a one-year history of asthma and FEV₁% of 88% and FEV₁/FVC of 70%, (B) mild bronchial wall thickening (1.3 mm) retrieved from a patient with asthma for one year and FEV₁% of 56% and FEV₁/FVC of 48%, and (C) moderate bronchial wall thickening (2.2 mm) in a patient with asthma for 19 years and FEV₁% of 75% and FEV₁/FVC of 84%. FEV₁%, predicted percentage of forced expiratory volume in one second; FEV₁/FVC, ratio of forced expiratory volume in one second to force vital capacity; HRCT, high-resolution computed tomography.

Figure 2

Assessment of bronchial dilation and mucus impaction in chest HRCT. HRCT manifestations of (A) cylindric bronchial dilation with “arrows” indicating lack of tapering greater 2 cm distal to bifurcation, and “arrowhead” referring visibility of peripheral airways), (B) varicose bronchial dilation (arrow) and mucus impactions (arrowhead), and (C) varicose bronchial dilation (arrow) and mucus impactions (arrowhead). FEV₁%, predicted percentage of forced expiratory volume in one second; FEV₁/FVC, ratio of forced expiratory volume in one second to force vital capacity; HRCT, high-resolution computed tomography.

Figure 3

Manifestation of emphysema, mosaic lung attenuation, and atelectasis in chest HRCT. HRCT manifestations of (A) centrilobular emphysema (arrowhead) and subpleural emphysema (arrow), (B) mosaic lung attenuation, areas of decreased lung attenuation (arrow) and increased lung attenuation (arrowhead), and (C) atelectasis (arrowhead) and “tree-in-bud” (arrow). FEV₁%, predicted percentage of forced expiratory volume in one second; FEV₁/FVC, ratio of forced expiratory volume in one second to force vital capacity; HRCT, high-resolution computed tomography.

Figure 4

The incidence of patients with different number of abnormal HRCT findings. Percentage of patients with normal HRCT is showed in bar A, and bar B to F represent one to five abnormal manifestations of HRCT, respectively. HRCT, high-resolution computed tomography.