(Chest. 2005;128:3545-3550.)
© 2005
American College of Chest Physicians
Accuracy of Virtual Bronchoscopy for Grading Tracheobronchial Stenosis*
Correlation With Pulmonary Function Test and Fiberoptic Bronchoscopy
David Shitrit, MD;
Postinikov Valdsislav, MD;
Ahuva Grubstein, MD;
Daniele Bendayan, MD;
Maya Cohen, MD and
Mordechai R. Kramer, MD, FCCP
* From the Pulmonary Institute and Department of Radiology, Rabin Medical Center, Beilinson Campus, Petah Tiqva, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Correspondence to: Mordechai R. Kramer, MD, FCCP, Pulmonary Institute, Rabin Medical Center, Beilinson Campus, Petah Tiqva 49100, Israel; e-mail: davids3{at}clalit.org.il
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Abstract
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Study objectives: To compare the accuracy of virtual bronchoscopy (VB) with fiberoptic bronchoscopy (FOB) and pulmonary function testing (PFT) for the assessment of tracheal stenosis and bronchial anastomotic stenosis.
Design: Prospective case series.
Setting: Pulmonary institute of major tertiary university-affiliated center.
Patients: The study group included 10 lung transplant recipients and 13 patients with central airway stenosis.
Interventions: All patients underwent PFT, VB, and FOB. All cases were graded by each modality on a scale of 1 to 3, and the findings were compared between modalities.
Results: Mean ± SD stenosis score was 2.0 ± 0.79 for PFT, 1.62 ± 0.73 for FOB, and 1.82 ± 0.77 for VB. A statistically significant correlation was found between VB and FOB scores (p < 0.0001, r = 0.76) and between VB scores and PFT (p = 0.03, r = 0.45). There was no correlation between PFT and FOB.
Conclusions: VB grading of tracheobronchial stenosis is well correlated with PFT. VB may be used to evaluate patients with known tracheobronchial stenosis after treatment and thereby reduce the frequency of repeated invasive FOB performed for that purpose. The correlation of VB with PFT may improve the reliability of this approach.
Key Words: CT • fiberoptic bronchoscopy • pulmonary function testing • virtual bronchoscopy
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Introduction
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Virtual bronchoscopy (VB) is a novel CT-based imaging technique for the noninvasive intraluminal evaluation of the tracheobronchial tree.1 Several studies23 have shown that VB can accurately show the lumen and diameter of the trachea, the left and right mainstem bronchi, and the bronchial tree down to the fourth order of bronchial orifices and branches. VB is being increasingly used to evaluate central airway disease and especially to detect benign and malignant airway stenosis.45 VB estimates of the grade of tracheobronchial stenosis resulting from either endobronchial pathology or external compression were found to be correlated with findings on flexible bronchoscopy.6 VB also proved to be slightly more accurate than axial CT for the diagnosis of clinically relevant stenosis at bronchial anastomoses in lung transplant recipients.7 However, there are no correlational data on VB and functional tests in patients with tracheobronchial stenosis. The aim of the present prospective study was to compare the accuracy of VB with that of fiberoptic bronchoscopy (FOB) and pulmonary function testing (PFT) for the assessment of bronchial anastomotic stenosis in lung transplant recipients and in patients with central airway stenosis.
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Materials and Methods
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Patients
The study group consisted of 23 patients with known stenosis of the major airways: 10 lung transplant recipients with bronchial anastomotic stenosis and 13 patients with subglottic (tracheal) stenosis secondary to prolonged intubation (n = 10) or Wegener granulomatosis, sarcoidosis, or endobronchial breast metastases (n = 1 each). All patients were examined in our pulmonary institute between March and November 2004, and all underwent PFT followed by VB and FOB. The study protocol was approved by our local ethics committee, and written informed consent was obtained from the patients before all procedures.
PFTs
Data on FEV1 and forced inspiratory flow (FIF) were recorded during spirometry. For the patients with bronchial anastomotic stenosis, only FEV1 was tested. Grading was as follows: FEV1 grade 1, 70 to 90% of predicted; FEV1 grade 2, 50 to 70% of predicted; FEV1 grade 3, < 50% of predicted; FIF grade 1, < 50% of predicted; FIF grade 2, 30 to 50% of predicted; FIF grade 3, < 30% of predicted..
VB
VB examinations were performed with a multidetector CT scanner (Asteion; Toshiba; Tokyo, Japan) with the following parameters: collimation, 4 x 2 mm; pitch, 1.375 (corresponding to manufacturer pitch of 5.5); rotation time, 0.75 s; 120 kilovolt peak; and 100 to 180 mA. Acquisition time was roughly 30 s, so that acquisition could be completed during a single breath hold. The thorax was scanned during inspiration in a caudocranial direction. After power injection of 80 mL of iopromide (Ultravist; Schering; Berlin, Germany) [flow rate, 2 mL/s; scan delay, 30 s]. Reconstruction intervals and slice thickness were 2 mm.
The axial CT images were transferred to a work station (Advantage Windows 4.0; General Electric Medical Systems; Milwaukee, WI) equipped with two 450-MHz central processing units and 512 megabytes of random access memory. Reconstruction software was used for two-dimensional and multidimensional reconstructions of the VB image, with calculation of the intraluminal stenosis area. Reformatted coronal and sagittal images of the tracheobronchial tree were produced.
To calculate the degree of stenosis, we compared the stenosis diameter measured on the images to the prestenosis diameter. We defined prestenosis diameter as the diameter of the normal airway immediately proximal to the stenosis. Three grades were assigned: grade 1, stenosis of 10 to 30% (compatible with 49 to 81% of the prestenosis diameter); grade 2, stenosis of 20 to 50% (compatible with 25 to 64% of the prestenosis diameter); grade 3, for stenosis of 40 to 70% (compatible with 9 to 36% of the prestenosis diameter).
FOB
FOB was performed by an experienced pulmonologist using a videobronchoscope (Olympus BF-P240; Olympus; Tokyo, Japan) under sedation and local anesthesia. Monitoring during bronchoscopy included pulse oximetry, ECG, and BP measurements. The mean interval between VB and FOB was 8.2 days (range, 1 to 16 days). To provide a standard of reference, the pulmonologist who performed the FOB was blinded to the results of the PFTs or VB. Tracheobronchial narrowing was graded semiquantitatively as follows: grade 1, luminal narrowing of less than one third; grade 2, luminal narrowing greater than one third and less than two thirds; grade 3, luminal narrowing greater than two thirds.
Statistical Analysis
Pearson correlation coefficient (r) and significance (p values) were calculated between the variables. To analyze differences in the distribution of categorical data, 
2 test or Fisher Exact Test was used, as appropriate; p < 0.05 was considered significant.
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Results
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Tables 1, 2
describe the clinical characteristics of the 13 patients with tracheal stenosis and the 10 lung transplant recipients, respectively. Mean age ± SD of the whole study population sample was 57.8 ± 17 years. Mean FEV1 was 59.5 ± 20% of predicted, and mean FIF in the patients with tracheal stenosis was 49.2 ± 22 L. No significant difference was noted between the two study groups in the FEV1 parameter.
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Table 2.. Clinical Characteristics of the Lung Transplant Recipients With Bronchial Anastomotic Stenosis Including PFT Results (n = 10)*
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The most common cause of tracheal stenosis was prolonged intubation. Tables 1, 2 detail the treatment for the stenosis (laser, stents, and brachytherapy) and PFT findings. Figures 1234
present VB of two patients, one with bronchial stenosis and one lung transplant recipient with bronchial anastomotic stenosis before and after stent insertion. Table 3
presents the stenosis diameters, areas, and grades for each patient by VB modality. Mean stenosis score for the whole sample was 2.0 ± 0.79 for PFTs, 1.62 ± 0.73 for FOB, and 1.82 ± 0.77 for VB.
Figures 5, 6
summarized the comparisons of the three modalities in the patients with tracheal and bronchial anastomotic stenosis, respectively. There was a statistically significant correlation between the VB and FOB scores (p < 0.0001, r = 0.76), and between the VB and PFT scores (p = 0.03, r = 0.45). No correlation was noted between PFTs and FOB (p = 0.2, r = 0.28).
Complete correlation was noted between all three modalities in 9 of 13 patients with tracheal stenosis but only in 3 of 10 patients with bronchial anastomotic stenosis. Correlation between VB and PFTs was noted in 12 of 13 patients with tracheal stenosis and in 5 of 10 patients with bronchial anastomotic stenosis. All other patients had a difference of only one score between VB and PFTs.
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Discussion
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The proper management of airway disease includes accurate diagnosis with evaluation of airway patency, lesion length, and cross-sectional area. These usually require invasive procedures, such as conventional flexible endoscopy, which is not without risk to the patient. Thanks to recent technological advances in medical imaging, physicians can now use volumetric chest CT for tridimensional exploration of the bronchial tree.8 VB makes it possible to navigate airways and to determine the exact location of the stenosis in relation to the extrabronchial structures.9
Another potential role for VB is evaluation of bronchogenic carcinoma. Finkelstein et al10 found that VB had a sensitivity of 100% for the detection of obstructive lesions and of 83% for detection of endoluminal nonobstructive lesions; however, its sensitivity for mucosal abnormalities was 0% and specificity was 100%. Rapp-Bernhardt et al11 reported similar results in a comparison of VB and FOB. Using VB, clinicians can appreciate not only the intraluminal proliferation of the tumor but also the extraluminal extension of the mass and its relation to the bronchial tree. However, because VB is unsuitable for the detection of subtle mucosal lesions, it cannot be used to identify premalignant lesions in the respiratory tract.10
VB may also aid clinicians in visualizing external, nonmucosal compressions on the bronchial wall that cause bronchial stenosis. These compressions may be due to normal anatomic structures, such as the aortic arch or esophagus, or to pathologic structures, such as enlarged lymph nodes, fibrotic masses, and extraluminal tumor. With VB, the location and source of the external compression can be defined. However, small compressions are difficult to detect and may be underestimated in 25% of patients.12 VB is also useful in patients who require endobronchial evaluation but cannot undergo FOB.
In the present study, we found the evaluation of bronchial stenosis by VB to be highly correlated not only with FOB, as reported previously, but also with PFT. To the best of our knowledge, this is the first report of the correlation of VB and PFT, including FEV1 and FIF. By contrast, FOB findings were not correlated with PFT. The close correlation of VB with these modalities makes the grading of the significant tracheobronchial stenosis more accurate, thereby improving the assessment.
We also applied VB to assess bronchial anastomotic stenosis in lung transplant recipients. Bronchial stenosis remains an important complication of lung transplantation, occurring in 10 to 15% of lung transplant recipients.13 When severe, the stenosis can lead to progressive, often debilitating airflow obstruction that may be difficult to clinically differentiate from other causes of airflow limitation, such as bronchiolitis obliterans syndrome.14 The correct diagnosis is important because, in most cases, the stenosis can be successfully treated with laser or by dilation and stent placement.15 FOB is the current standard for diagnosis of anastomotic complications, including stenosis.16 However, it is invasive and may not be well tolerated. FOB also provides only limited information on the length of the stenosis or the patency of the distal airways, which are important factors in planning treatment.17 Because VB correlates with PFT, it may be useful as a screening examination in lung transplant recipients with suspected bronchial or anastomotic stenosis.
Although VB proved to be reliable for the quantitative assessment of tracheobronchial stenosis because it produced more realistic images of the narrowed bronchial lumen, it has some limitations. Reproducible quantitative measurements of the bronchial diameter are difficult and cannot depict mucosal color and texture.18 VB also does not allow for the endoluminal visualization of the tracheobronchial tree or the therapeutic and diagnostic maneuvers, such as obtaining culture and biopsy specimens or removing foreign bodies,19 that are possible with FOB.
Other limitations of VB include radiation doses when procedures are repeated, and difficulty in depicting malacia of the trachea or the bronchia and visualizing small findings such as granulomas or vegetations. Furthermore, the VB aspects of the spurs are usually quite different than the real ones and have a thicker appearance.
Nevertheless, VB may provide important diagnostic and potentially therapeutic information before FOB is undertaken. It can also be used to evaluate patients with known tracheobronchial stenosis after treatment and may thereby reduce the frequency of repeated invasive FOB performed for that purpose.
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Acknowledgements
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We thank Nizan Zohar, head technician of the CT department, for his support in preparation of this project.
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Footnotes
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Abbreviations: FIF = forced inspiratory flow; FOB = fiberoptic bronchoscopy; PFT = pulmonary function testing; VB = virtual bronchoscopy
Received for publication March 21, 2005.
Accepted for publication May 31, 2005.
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References
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Abstract
Introduction
