With the results of the national lung cancer screening trial showing a reduction in mortality with screening high-risk patients,1 the peripheral lung nodule has come front and center in medicine, and not just pulmonary medicine.
As greater numbers of nodules creep into clinical practice, there is a focus on identifying the best method to diagnose them. Emerging technologies such as electromagnetic navigation and virtual bronchoscopy have been developed to assist the bronchoscopist with locating peripheral lesions, although they presently lack the ability to provide real-time procedure feedback about the location of the device relative to the target lesion.
The radial endobronchial ultrasound (EBUS) miniprobe was the first successful application of ultrasound in the airways and is not a true navigational tool, rather a confirmatory one. Radial EBUS for peripheral nodules relies on the bronchoscopist’s ability to locate a lesion using knowledge of airway anatomy and the ability to interpret a computed tomography scan. Once the probe has been positioned accordingly and the radial probe is turned on, the resulting image provides the bronchoscopist with real-time procedural feedback regarding probe position relative to the target lesion.
The article by Hsia and colleagues in this issue of the Journal of Bronchology and Interventional Pulmonology examines the yield of sampling tissue from peripheral pulmonary lesions using radial EBUS guidance in a heterogeneous patient population with a lower prevalence of malignancy. Their results indicate that this technique is applicable to benign and malignant processes, with yields comparable with those obtained by other methods. Their findings also suggest that radial EBUS-assisted biopsy of peripheral nodules may not be affected by factors such as an air bronchus sign, which has been shown to increase the yield of electromagnetic navigation.2
The use of radial EBUS takes advantage of what pulmonologists are trained to do during fellowship: target an area of abnormality on chest imaging, estimate its location anatomically, and try to sample it in the lung periphery using brushes, forceps, or needles. The concept of taking the miniprobe and advancing it through the working channel into the lung parenchyma is no different than placing any other instrument into the lung through the bronchoscope. Once the bronchoscopist is comfortable identifying lesions by ultrasound in the lung periphery using radial EBUS, he or she will have the added assurance that biopsies are being performed in the appropriate location. Radial EBUS, in a way, is a metric for how accurately one can locate a lesion using a chest computed tomography scan. The bronchoscopist is the navigational tool, and the radial probe is real-time intraprocedure feedback confirming the location of the target lesion.
So where does this technology fit into the evolving algorithm in the evaluation of the pulmonary nodule? Imagine driving at night in a car with no headlights, but with a mapping system that takes you to a destination, and compare that to driving a car with headlights, but no guidance or mapping. In the former scenario, you have a system that not only tells you where to go but also where to stop. The only problem is that you cannot look out the window to know that you have wound up exactly where you want to be. In the latter scenario, you can see where you are going, but may not have the guidance to get you to your destination in a timely manner, or at all; however, if you find your target, you will be able to see it and know that you are there.
Electromagnetic navigation and radial EBUS approach the pulmonary nodule in different and potentially complementary ways. The optimal approach may be a combination of the 2 techniques, and prior publications have demonstrated this, showing that navigation and radial EBUS combined to have a better yield than either method alone.3 The potential benefits of this pairing will need to be further explored.
Time will tell which, if any, of these technologies will persevere, but it is clear that the pulmonary nodule will continue to challenge the bronchoscopist regardless of what technique or technology is used.
1. The National Lung Screening Trial Research Team. . Reduced lung-cancer mortality with low-dose computed tomographic screening. N Engl J Med. 2011;365:395–409
2. Seijo LM, Torres JP, Lozano MD, et al. Diagnostic yield of electromagnetic navigation bronchoscopy is highly dependent on the presence of a bronchus sign on CT imaging-Results from a prospective study. Chest. 2010;138:1316–1321
3. Eberhardt R, Anantham D, Ernst A, et al. Multimodality bronchoscopic diagnosis of peripheral lung lesions: a randomized controlled trial. Am J Respir Crit Care Med. 2007;176:36–41