Lung Tumor Airway Obstruction Overview

Subacute and chronic upper airway obstruction is a serious problem in adult pulmonary practice. The upper airway, from the vocal cords though the trachea and into the right and left main bronchi, may be compromised by benign fibrous stictures, or by malignant intra or extraluminal tumors. Frequently patients presenting complaint is wheeze and breathlessness, and in the absence of other symptoms such as hemotysis, they are often considered to have asthma tahter than upper airway obstruction. The diagnosis is often further compounded as the plain chest radiograph may be completely normal. By the time a characteristic stridor develops, and the clinical diagnosis of upper airway obsturction is made, the patients often have a significantly compromised airway, with a luminal diameter of 4mm or less. This diagnosis may be supported clinically by an abnormal flow volume loop, which can demonstrate the presence of the upper airway obsturction and help locate the obstruction as intra or extra thoracic.

The assessment of the upper airway is adied by laryngoscopy, which can examine the larynx to the level of the cords and sometimes note a sub-glottic stenosis. In the past, lateral tomography of the tracheal air column, and more recentlyCT scanning have been helpful to localize and describe an obstructing or partial obstructing segment. However, the utility of these procedures is limited, especially with the assessment of the right and left main bronchi, which are usually cut tangentially by the CT scan, and therefore difficult to interpret. Bronchoscopic assessment, using flexible bronchoscopes, has been helpful but is also limited in that the proximal end of a severe stenosis can be seen, but the airways distal to that cannot be seen, and frequently the distal extent of the stenosis therefore cannot be evaluated.

currently, there are a number of therapeutic modalities fot the management of upperairway obstruction in the adult and some of these methods are complimentary. These methods include balloon bronchoplastt;stent placement, using either a fitted silicon stent or a metal expandable stent, laser ablation with carbon dioxide of Nd-YAG lasers, or brachytherapy. In some patients, surgical resection fo the obstructing segment is necessary. Sometimes all therapeutic mocalities are used. Careful planning of therapy is crucial, both for a satisfactory outcome of the stenosis, and for patient safety.

In planning the appropriate managment, it is essential to know the pathological nature of the stenosis (i.e. benign or malignant) and whether it is predominantly intraluminal, or extra luminal which generally requires a flexible bronchoscopy. Prior to the bronchoscopy, it is important to have some knoweledge of the diameter and length of the stenosis, the site, whether it is a single stenosis, or part of a series of multiple stenoses, and the relationship of the stenosis to surrounding structures such as supra sternal notch, blood vessels or esophagus. Following these assessments, it is essential that the airway abnormalities be now accurately defined anatomically and pathologically, so that appropriate treatment can be planned and safely instituted.

To measure the cross-sectional area of a tube using VIDA's Tube Geometry Analysis program, it is first necessary to segment the air within the airway from the surrounding tissue. To determine the proper threshold for segmentation, the half-max value of the inner wall was measured seperately for the before and after scans using VIDA's Region of Interest (ROI) program.

First, a line was drawn from the inside of the lumen past the inner wall of the airway. Using the ROI Graph panel intensity cross was selected from the graph types menu and generate point from the measure menu. Left-clicking on the graph, causes a line to appear. Next, one must drag the line so it falls half way between the minumum and maximum of the graph, the "half-max". Once the left mouse button is released the value at that point will be recorded in the ROI: Stats panel, which is the half-max for the airway wall. Several half max measurements were made on different slices. An average of the half-max for each data set was calculated seperately and used as the threshold for segmentation. For more information about using the Region of Interest program.

Segmentation of the airways was accomplished with VIDA's 2D Segmentation program. First, the entire data set must be multiplied by 90 percent to allow the airway to be a unique object. Next, the half-max value of the inner wall determined with ROI is set as the 2D fill threshold. Everything below the threshold is set to be a fixed value of 255. For more information about using the 2D Segmentation program.

Multishape Based Interpolation was used to interpolate the segmented data sets (The original image (x,y,z)(0.684,0.684,3.0) was converted to cubic voxels (x = y = z)). For more information about using the Multishape Based Interpolation program.

Last, Tube Geometry Analysis was used to calculate the true centerlines of the airways from which the cross-sectional area was measured. For more information about using the Tube Geometry Analysis program.

Last modified: Fri Jun 4 10:42:14 CDT