Multi-detector CT evaluation in patients suspected of tracheobronchomalacia: Comparison of end-expiratory with dynamic expiratory volumetric acquisitions

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Abstract

Purpose

The aim of this study was to compare dynamic expiratory imaging and end-expiratory imaging using multi-detector CT (MDCT) of the central airways in patients suspected of tracheobronchomalacia (TBM).

Methods

This study had local ethical committee approval. Seventy patients suspected of TBM were prospectively included. All patients underwent evaluation of central airways by three different low-dose MDCT acquisitions: end inspiration, end expiration, and dynamic expiration. Degree of airway collapse was measured by calculating the percentage change in the area and diameter of the airways between inspiratory and the two expiratory techniques at three levels of the trachea and in the sagittal diameter of the right and left main bronchi. Three threshold levels of percentage reduction in diameter or area (30%, 50%, and 70%) for defining TBM were evaluated.

Results

In the entire population, the mean percentage of airway collapse was significantly greater with dynamic expiratory imaging than with the end-expiratory imaging at three different levels: lower thoracic trachea (26% vs. 16.6%, p < 0.009), right (25.2% vs. 14%, p < 0.01) and left main (24.7% vs. 13.3%, p < 0.01) bronchus. Whatever the threshold value for defining TBM, dynamic expiratory imaging always resulted in diagnosing TBM in more patients than end-expiratory imaging.

Conclusions

Dynamic expiratory imaging shows a significantly greater degree and a significantly greater extent of airway collapse than standard end-expiratory imaging in patients suspected of TBM. Further evaluation of the clinical relevance of such findings is warranted.

Introduction

Acquired tracheobronchomalacia (TBM) is an airway disorder resulting from increased compliance and excessive collapsibility of the central airway [1], [2]. Apart from this functional definition, the anatomical definition of TBM is still unclear since the classical definition is based on an airway collapse ≥50% at expiration or during coughing [3], [4]. Other authors propose a threshold value of 70% for airway collapse [5] or a more than 28% change in the midtracheal cross-sectional area [6]. This lack of identified threshold for defining disease is explained by the difficulties of conducting studies in the general population using invasive tools (fiberoptic bronchoscopy) or CT imaging that is associated with a significant amount of radiation.

However, since TBM is an important cause of non-specific pulmonary symptoms but is largely under diagnosed [7], new diagnostic strategies should be investigated. This is particularly true as new therapeutic interventions can now be proposed such as non-invasive ventilatory support [8], airway stenting [2], or surgery [9]. Traditionally, TBM has been identified using fiberoptic bronchoscopy. Non-invasive diagnosis of TBM has been demonstrated using fluoroscopy [1], conventional CT with inspiratory–expiratory acquisitions [6], and electron beam CT with dynamic acquisitions [3], [5]. Retrospective studies by Gilkeson et al. [10] and Baroni et al. [11] emphasized the promising results of dynamic expiration, multi-detector row CT (MDCT) acquisitions for demonstrating airway collapse.

The aim of this prospective study was to compare dynamic expiratory imaging and end-expiratory imaging using multi-detector CT (MDCT) of the central airways in patients suspected of tracheobronchomalacia (TBM).

Section snippets

Patient population

Seventy consecutive patients who were clinically suspected of TBM on clinical and functional data were prospectively included in this series between November 1, 2003 and February 9, 2005. There were 43 men (61%) and 27 female (39%) who ranged in age from 12 to 79 years (mean age, 57 years). 33 of 70 (47%) of the patients were current or former smokers; 19 of 70 (27.1%) of the patients were referred with a history of chronic cough, 56 of 70 (74%) complained of chronic dyspnea. 37 of 70 (52.9%)

Results

The measurements of the cross-sectional area of the trachea at the three predefined levels and of the sagittal diameter of the main stem bronchi were always possible.

There was a high interobserver reliability throughout all the cross-sectional area measurements. Kappa measures were 0.8 and 1.0 for the 50% (end-expiration) and 30% (end and during expiration) thresholds, respectively. This corresponds to substantial (0.8) and almost perfect agreement (1.0). As a consequence, the results for the

Discussion

The results of our study show that MDCT acquisition during dynamic expiration was significantly more sensitive for diagnosing airway instability, than the end-expiratory acquisition. Moreover, the extent of the abnormal collapse at one or more of the five anatomical levels that we have evaluated was significantly greater on dynamic expiratory imaging as compare to end-expiratory imaging.

TBM is caused by weakness of the airway walls and supporting cartilage [2], [15], [16]. TBM is an important

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