Maybe we should do more thoracic CT...

AJVR 2024

February 06, 2025

Charlotte Gerhard, Isabelle Masseau, Aida Vientos-Plotts, et al

Background
Bronchomalacia (BM) in dogs, characterized by dynamic airway collapse, is a significant cause of respiratory morbidity. Traditional diagnostic methods like bronchoscopy may underestimate its severity. Quantitative computed tomography (CT) attenuation analysis, a radiomics-based approach, offers objective metrics to characterize parenchymal changes related to BM. This study hypothesizes that inspiratory and expiratory CT lung attenuation metrics could distinguish BM from non-BM (NoBM) in dogs.

Methods
A retrospective analysis was performed on CT data from 123 client-owned dogs diagnosed with BM and 20 control dogs (NoBM). Inspiratory and expiratory breath-hold CT scans were analyzed using 3D Slicer software to quantify metrics like mean lung attenuation (MLA), percentage of low-attenuation area (LAA) at −856 HU, high-attenuation area (HAA) at −700 HU, and attenuation area (AA) between −600 and −250 HU. Statistical analyses included beta regression and ANOVA, accounting for slice thickness and respiratory phases.

Results
-MLA: Dogs with BM showed a greater increase in MLA from inspiration to expiration compared to NoBM (22% vs. 11%, respectively; P = .001), indicating impaired parenchymal aeration.

-LAA at −856 HU: Decreased significantly in BM dogs compared to NoBM (P = .016), suggesting reduced low-density areas during expiration.

-HAA at −700 HU and AA between −600 and −250 HU: Both metrics increased more significantly in BM than NoBM during expiration (P < .001), reflecting parenchymal densification associated with airway collapse.

-Kurtosis and Skewness: BM dogs exhibited lower values, indicating increased heterogeneity of lung parenchyma.

-CT imaging revealed dynamic attenuation changes that correlated with segmental and subsegmental airway collapse.

Limitations
-Limited NoBM group size and retrospective study design may constrain generalizability.
-Variability in CT protocols and comorbid conditions in BM dogs could influence attenuation metrics.
-Human-derived CT metrics were adapted for veterinary use without established canine-specific references.

Conclusions
Quantitative CT metrics effectively documented parenchymal changes in BM-affected dogs, demonstrating the utility of radiomics in complementing traditional diagnostic methods. These findings highlight the potential of quantitative CT analysis in advancing the diagnosis and monitoring of BM and other lung diseases in veterinary medicine. Prospective studies are needed to establish reference values across diverse canine populations.

A—Inspiratory (A) and expiratory (B) breath-hold CT images of a 12-year-old female spayed Miniature Schnauzer with severe (grade III) BM. On inspiration, segmental (white arrows) and subsegmental (arrowheads) airways are opened and have a relatively circular shape. Most of these airways collapse or are severely narrowed during expiration. On expiration, the pulmonary parenchyma is markedly increased in attenuation especially surrounding the collapsed airways, reflective of impaired downstream parenchymal aeration. Standardized nomenclature is used to describe segmental and subsegmental airways. B—Inspiratory (C) and expiratory (D) breath-hold CT images of a 12-year-old female spayed Border Collie without BM. On inspiration, segmental (white arrows) and subsegmental (arrowheads) airways are opened and have a relatively circular shape. On expiration, the airways maintain their shape although they are slightly narrower than on inspiration. Overall, the lung parenchyma is minimally increased in attenuation on expiration compared to inspiration although it remains homogenous including that surrounding the airways. A sedated upper airway examination revealed complete lack of abduction of the arytenoid cartilages on inspiration diagnostic for laryngeal paralysis. Tracheobronchoscopy showed hyperemia and increased vascularity of the proximal trachea and the distal trachea and bronchi were unremarkable. These changes were consistent with gastroesophageal reflux. Ao = Descending aorta. CVC = Caudal vena cava. E = Esophagus. LB2 = Left caudal lobar bronchus. LB2V2 = Second ventral segmental bronchus of LB2. RB3D1 = First dorsal segmental bronchus emerging from the right accessory lobar bronchus. RB3V2 = Second ventral segmental bronchus from the right accessory lobar bronchus. RB4 = Right caudal lobar bronchus. RB4D2 = Second dorsal segmental bronchus of RB4. RB4V1 = First ventral segmental bronchus of RB4.

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