Endobronchial Ultrasound: Is it Ready for Prime Time?

Endobronchial ultrasound (EBUS) has emerged in the last decade as a new advancement in the field of interventional pulmonology.1 It gives bronchoscopists an opportunity to see beyond the airway, allowing analysis of the airway structure and processes surrounding the airway. EBUS is a new diagnostic tool with great potential for the evaluation of the airway and for the diagnosis of lung cancer as well as for lung cancer staging. The development of EBUS started in the early 1990s when the radial probe EBUS was used for the evaluation of the structure of the airway as well as the lung parenchyma, pulmonary artery, and metallic stent assessment.2 Two types of EBUS are now available for clinical use: the radial probe EBUS and the convex probe EBUS. The miniaturized 20-MHz radial probes are fitted with a catheter that carries a water-inflatable balloon at the tip. The balloon optimizes the contact between the probe and the bronchial wall and allows visualization of detailed images of the bronchial wall structure as well as the surrounding structures.3 Recently, a smaller ultraminiature radial probe has been introduced that can be used for detection of peripheral intrapulmonary nodules.4 Although the radial probe EBUS allows imaging of the airway, the lung parenchyma, and the surrounding structures, one is limited to performing real-time procedures due to the fact that the probe must be inserted through the working channel of a bronchoscope. On the other hand, the convex probe EBUS first introduced in 1993 is an endoscope with a built-in linear probe ultrasound on the tip that enables real-time endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA).5 In the July 2008 issue of Journal of Bronchology, Shirakawa et al6 tried to solve the controversies of the number of layers of the central airway that can be visualized by the high-frequency radial probe EBUS. Some investigators have claimed 5 layers,3,7 others found 6,8 or even 7 layers.9 They used postmortem tracheal specimens that were prepared for 3 different analyses. One was prepared with complete surrounding structures, 1 with removed adjacent mediastinal tissue, and 1 after the removal of the external fibroelastic tissues. They come to a conclusion after analyses of the different types of specimens prepared in their in vitro study that there are 7 layers in the structure of the central airways described by EBUS imaging. Although their thorough examination of the different layers visualized by the radial probe EBUS is encouraging, it highlights the complexity of the images of the central airway obtained by EBUS. It is perhaps too complex for bronchoscopists performing routine bronchoscopy, which may contribute to the less frequent usage of the radial probe for analyses of the airway. The radial probe EBUS has been used mainly for the evaluation of the depth of tumor invasion in early lung cancer.3,7–11 Although the number of layers in the structure of the airway differs among the different investigators, there is no disagreement about the imaging of the mucosa, submucosa, and the internal surface of the cartilage. Indeed it has been shown by different investigators that the management of central-type bronchial carcinomas depends on the depth of tumor invasion.8,10 Lesions invading the cartilage should be surgically resected as opposed to lesions which have not invaded the cartilage that can be treated with other minimally invasive modalities, such as laser ablation and photodynamic therapy.12,13 Hence, it is questionable whether the precise evaluation of the external layers, as shown in this study, is clinically important. The ultraminiature radial probe is a new type of probe that has been shown to be useful in fluoroscopy for guiding bioptic procedures of peripheral intrapulmonary lesions by the application of sheath catheters.14–17 According to the literature, it seems like the radial probe EBUS for peripheral pulmonary lesions is a more user-friendly device compared with the central-type EBUS and has attracted more bronchoscopists for use in clinical practice.4,14–17 However, due to the nature of the probe, it is still not a real-time procedure with target visualization. Although the radial probe EBUS is a useful tool, which can broaden the practice of interventional pulmonology, it is still underused as shown by the limited publications related to the procedure. One of the reasons is the complexity of the radial image as shown in this issue of the Journal.6 Clinicians are usually more used to the linear ultrasound image. The new convex probe EBUS enables real-time biopsy of the mediastinum and the hilum by EBUS-TBNA. The linear ultrasound images are easier to understand. After preliminary studies showing the efficacy of the convex probe EBUS in surgical lung specimens,5 the clinical use of the convex probe EBUS under local anesthesia for the assessment of mediastinal and/or hilar lymph nodes was first reported in 2004.18 It has only been 4 years since the initial report; however, the growing numbers of publications concerning the use of EBUS-TBNA for the evaluation of mediastinal lymph nodes in lung cancer staging and other benign diseases indicate the effectiveness of EBUS-TBNA in interventional pulmonology.18–30 Another important issue of incorporating new devices into clinical practice is the reimbursement for the procedure. Sheski and Mathur31 recently reported practical advice on documentation, coding, billing, reimbursement, and regulatory issues related to the EBUS procedure. However, due to the change in administrative medicine, it is not clear whether the same numbers can be applied today.32 Nevertheless, EBUS-TBNA will reduce the need of more invasive procedures such as mediastinoscopy and perhaps be used more by clinicians as documented in the new American College of Chest Physicians (ACCP) guidelines for invasive staging of lung cancer.33 Is EBUS ready for prime time? Whether it is the radial probe EBUS or the convex probe EBUS being used, there are several factors that need to be considered. Reimbursement of the procedure is one of the important issues. Physician reimbursement of EBUS seems to be marginal, especially for those with less experience.31 Whether hospitals will purchase the equipment necessary for EBUS-guided procedures is probably based on the overall picture of having the device. The ability to offer the minimally invasive procedures with high diagnostic yield may be associated with more referrals, which may lead to increased income. Learning the procedure and maintaining competency is another issue. According to the ACCP guidelines for interventional procedures, physicians should be supervised for 50 EBUS procedures and should perform 5 to 10 procedures per year to maintain competency for the radial probe EBUS.34 There are still no guidelines for performing EBUS-TBNA; however, training at specialized centers from experts and attending training courses are helpful before beginning the procedures. If they are performed by a well-trained operator in a proper setting, it is clear that EBUS-guided procedures will provide an accurate and safe approach to various lung diseases and avoid additional diagnostic procedures. Improved training systems and proper hospital credentialing are necessary before EBUS is ready for prime time.

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