Imaging the Airways

Comparison of three-dimensional virtual endoscopy with bronchoscopy in patients with oesophageal carcinoma infiltrating the tracheobronchial tree

Virtual endoscopy (VE) is a technique for performing simulated bronchoscopy using helical CT data of the tracheobronchial tree. In order to evaluate a virtual three-dimensional (3D) endoluminal procedure for the tracheobronchial tree, comparison was made between bronchoscopy, axial CT images and minimal intensity projections (MIP). 21 patients were referred for helical CT because of oesophageal carcinoma shown by bronchoscopy to infiltrate into the trachea or bronchi. Axial CT images obtained on a helical scanner were transferred to a Sparc20 workstation. VE was compared with the axial CT images and the MIP concerning additional information on the location and degree of stenosis gained after 3D reconstruction of the inner surface of the tracheobronchial tree. The accuracy of this VE system was compared with bronchoscopy. Follow-up was performed in two patients to evaluate the tracheobronchial system after stent implantation. All stenoses were identified by VE with no statistically significant difference in detection of location or grading of the stenosis to real time bronchoscopy. Passage of subtotal stenosis was only possible with VE. VE is suitable for following up stent implantation. Submucosal lesions of the tracheobronchial tree could not be detected by VE. There was no statistically significant difference regarding the location of the stenoses between VE, axial CT slices, MIP and bronchoscopy. The VE showed only a statistically significant difference with regard to the degree of stenosis which was underrated on axial CT slices and MIPs. Pitfalls including mucus plugs and wall defects due to the wrong threshold value were a limitation of VE. VE is presently too time-consuming to use in every patient with an infiltrating tumour into the tracheobronchial tree. In conclusion, while VE cannot replace endoscopy of the tracheobronchial tree or the oesophagus, it is an accurate and non-invasive method for identifying endoluminal tumours, grading stenoses and visualizing the tracheobronchial tree beyond stenoses in a small number of patients who are not amenable to endoscopy.

New techniques and developments in physiologic imaging of airways

Recently, noninvasive imaging methods for assessing regional and individual airway responsiveness have been developed in animal models and applied to humans with obstructive lung disease. This article examines the technique of high-resolution CT scan and MR imaging and their applications to the imaging of airways.

Paediatric tracheobronchomalacia and its assessment by tracheobronchography

Tracheobronchomalacia (TBM) is a rare condition that results in abnormal compliance of the airways with airway collapse being most marked in expiration. In a series of 28 patients, it was observed that a majority of cases presented with malacia involving the trachea (64%) and the left main bronchus (64%) alone. The right main bronchus was involved in combination with the trachea in 32%, but rarely was involved by itself. Most patients demonstrated associated congenital abnormalities, such as tracheo-oesophageal fistulae, vascular rings or congenital heart disease (78%). A small proportion were premature infants with no obvious associated abnormality (11%). Evaluation of the dynamic process, tracheobronchomalacia; requires 'real-time' investigation. While computed tomography (CT) and magnetic resonance imaging (MRI) have their role in the management of chronic airway obstruction in the child, only cine-CT, bronchoscopy, fluoroscopy and tracheobronchography provide real-time assessment for the evaluation of a dynamic process such as TBM. In our experience, tracheobronchography provides excellent anatomic, physiologic and therapeutic information in the assessment of those infants with primary or secondary TBM. By using continuous positive airway pressure in incremental doses, the amount of positive pressure required to maintain an open airway in expiration is a valuable adjunct to the clinical management of the patient. When careful attention is paid to technique, tracheobronchography is a safe investigation in experienced hands.