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Chest ❯ Virtual Bronchoscopy

ProblemVirtual bronchoscopy is used in both adults and pediatric patients for a range of conditions including intra-luminal pathology, accessory bronchi, vascular anomalies and their relationship to the airways, foreign bodies and infection (stenosis)
ProtocolThe study can be performed with or without IV contrast material and the use of IV contrast will depend on the clinical application of the study. The protocol is usually done in deep inspiration (surely not expiration) using a fast CT acquisition. CT protocol includes section thickness of usnder 1 mm with .75 mm at .5 mm intervals ideal. 3D maps including intraluminal views (use the virtual colonoscopy software) are ideal for most cases.
  1. Although curved multiplanar reformatted CT images provide considerable information about the disease patterns, VB has additional advantages of 3-dimensional display of pathology, which mimics the images of FOB. VB also can be used as a road map for navigation during transbronchial aspiration and biopsy of mediastinal and hilar masses
  2. The trachea is usually 9–15 cm long in an adult and begins at approximately the sixth cervical vertebra, at the inferior border of the cricoid cartilage. The diameter of the trachea is typically 2–2.5 cm. The trachea has two sections. The cervical portion is superior to the thoracic inlet. The intrathoracic portion extends from the thoracic inlet to the bifurcation (carina). The trachea is supported anteriorly by 16–20 C-shaped rings of cartilage. In the posterior aspect, the trachea consists of the pars membranacea. This membrane is flexible, allowing the trachea to change in configuration during inspiration and expiration. The membrane normally bulges during expiration and coughing.
  3. The mainstem bronchi pass inferolaterally from the carina into the lungs and are supported by cartilaginous rings. Both mainstem bronchi are accompanied into the hila by the main pulmonary arteries. In the hila, the mainstem bronchi branch to form the bronchial tree. The right and left mainstem bronchi branch into secondary lobar bronchi, three on the right and two on the left, which further branch into tertiary segmental bronchi, each bronchus supplied by a segmental artery. Each segmental bronchus–artery unit makes up a bronchopulmonary segment, a commonly used anatomic, functional, and surgical subdivision. The segmental bronchi continue to branch until reaching the terminal bronchioles, the smallest airway without alveoli.
  4. VB is being increasingly used to detect and grade benign and malignant airway stenosis. VB has been shown accurate in assessment of the stenotic width and length of fixed airway lesions. In a study by Burke et al. [6], correlation of stenotic shape and contour between VB and conventional bronchoscopy was excellent. The stenosis-to-lumen ratios determined with VB and conventional bronchoscopy were found to be within 10% of each other.
  5. There are limitations to using VB for evaluation of airway stenosis. First, retained mucus or blood can cause false-positive findings. Second, the mucosa cannot be visualized with CT, as is possible at conventional bronchoscopy. Third, the diameter of the airway on CT depends on the respiratory cycle. Stenosis can be underestimated on inspiration; therefore, VB for this indication is typically performed during expiration or, in some cases (e.g., tracheomalacia), during both inspiration and expiration. 
  6. VB can be easily used for identification of anatomic variants such as tracheal and bronchial diverticula. A tracheal diverticulum is characterized as an outpouching of the tracheal wall. Diverticula can be single or multiple and are identified during 1% of autopsies. Diverticula are usually asymptomatic but can trap secretions and can become infected. Patients present with cough, dyspnea, or repeated episodes of tracheobronchitis.
  7. Normal variants such as a tracheal bronchus can be identified with VB. Tracheal bronchus is a congenital aberrant bronchus present along the right side of the trachea above the carina, supplying the right upper lobe. Tracheal bronchus is usually an incidental finding but can be symptomatic if it acts as a reservoir for secretions or infection. An association between tracheal bronchus and other bronchopulmonary abnormalities has been reported.
  8. Kosucu et al. performed low-dose MDCT and VB on 23 children with clinically suspected foreign body aspiration. All patients also underwent conventional bronchoscopy. In 15 patients, the foreign object was identified with CT and conventional bronchoscopy. CT also has the advantage of showing secondary signs, such as hyperaeration, atelectasis, and infiltrates.

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