Grading Airway Stenosis Down to the Segmental Level Using Virtual Bronchoscopy: Flexible bronchoscopy procedures

Grading Airway Stenosis Down to the Segmental Level Using Virtual Bronchoscopy: Flexible bronchoscopy proceduresBecause virtual bronchoscopy has an interactive design, we used the multiview mode at the workstation in combination with axial CT scan slices and multiplanar reformats for analysis of the airways. This is particularly useful for orientation within the tracheobronchial tree, and permits differentiation between intraluminal tumor growth and extraluminal airway compression. Furthermore, axial and reformatted CT scan slices are an indispensable tool for thoracic CT diagnosis, providing important anatomic and pathologic information beyond the luminal view of a bronchoscope, and permitting the detection of adenopathy and neighborhood infiltration.

Virtual bronchoscopy uses surface rendering, which takes advantage of the natural contrast between the airway and surrounding tissues. Therefore, the level of thresholding is important for displaying accurate simulations. For displaying the central airways, we used an upper threshold between —400 and —550 HU. For virtual bronchoscopic reconstruction of segmental bronchi, we adapted the threshold to lower values of between — 500 and — 800 HU, depending on the individual caliber of the airways. We cannot fully exclude that this somewhat subjective choice may have caused overestimation or underestimation of the airway diameter.
An intrinsic limitation of virtual bronchoscopy is its inability to permit therapeutic and diagnostic maneuvers. As observed in our study, especially the segmental bronchi may be susceptible to the deposition of mucus and coagulated blood, which may be misinterpreted as stenosis on virtual bronchoscopy. These depositions can be removed through irrigation and suction on flexible bronchoscopy. Flexible bronchoscopy procedures, however, can be uncomfortable for the patient and may require sedation. In addition, complications relating to the procedure itself and anesthesia have been described. The complications of flexible bronchoscopy must therefore be weighed against the considerable amount of diagnostic and therapeutic information gained from the procedure.