Introduction:
Endobronchial ultrasonography represents an innovative tool enabling bronchoscopists to extend their visual reach beyond the airway. While conventional bronchoscopy examination is limited to the internal surface of the airway, EBUS offers the capability to assess both the airway structure and surrounding processes. Overcoming initial technical challenges in applying ultrasonography to bronchoscopy practice, the radial probe EBUS was commercially introduced in the 1990s. EBUS is a promising diagnostic instrument for airway evaluation, lung cancer diagnosis, and staging. Clinical EBUS involves two main types: radial probe EBUS and convex probe EBUS. Here, we will learn more about radial EBUS.
What Is Radial Endobronchial Ultrasound?
The miniaturized -MHz radial probe initially aimed to enhance bronchial wall imaging, facilitating the assessment of tumor infiltration into airways, which is particularly beneficial for early lung cancer and advanced disease evaluation. Additionally, the radial probe EBUS facilitates visualization of mediastinal and hair lymph nodes, improving the yield of transbronchial needle aspiration (TBNA) for lung cancer staging.
An even smaller ultraminiature radial probe has emerged, possibly inserted into the bronchoscope’s channel to detect peripheral intrapulmonary nodules. Studies have demonstrated that EBUS can replace fluoroscopy in guiding biopsy procedures for peripheral intrapulmonary lesions using sheath catheters. However, due to its probing nature, real-time visualization remains a challenge.
What Are the Applications of Radial Endobronchial Ultrasound?
Lung Cancer Assessment:
Originally developed for central airway evaluation, the radial probe EBUS has been found useful in managing patients with early lung cancer. Notably, it aids in detecting premalignant lesions or small intrabronchial tumors that may be invisible on radiographs but are discovered incidentally or through screening in high-risk individuals. Treatment decisions in such cases hinge on the extent of tumor invasion within the bronchial wall layers, a distinction conventional radiographic imaging cannot provide. In contrast, the radial probe EBUS can discern alterations in the multilayer structure of the bronchial wall, especially for small tumors.
Comparative analysis of ultrasonogram and histological findings in lung cancer cases demonstrated an accurate depth of tumor invasion in 95 percent of lesions using R-EBUS. Furthermore, radial EBUS has been shown to enhance specificity in predicting malignancy in small lesions that were autofluorescence-positive but negative on white light bronchoscopy.
Photodynamic therapy stands out as a leading treatment modality for early-stage lung cancer, particularly in non-invasive cases. Therefore, an accurate assessment of the extent of tumor invasion is paramount before treatment initiation.
Beyond its application in early-stage lung cancer, EBUS proves beneficial in evaluating advanced cases. For centrally located lung cancers, preoperative assessment of tumor spread is crucial for determining resectability. A trial comparing EBUS and chest CT demonstrated EBUS’s superior accuracy in assessing airway involvement by central intrathoracic tumors. EBUS emerges as a more precise tool than conventional imaging for predicting T4 disease in lung cancer.
Mediastinal Tumor Diagnosis:
Radial probe EBUS enables precise localization of mediastinal tumors by carefully assessing their mediastinal tumors by carefully assessing their relation to surrounding structures. Studies indicated that EBUS is superior to conventional radiographic imaging in detecting tumor infiltration into mediastinal organs. EBUS effectively distinguishes between vascular abnormalities, fluid, and solid structures when airway compression occurs. Despite its effectiveness in imaging the mediastinum, there are limited reports on performing biopsies of mediastinal tumors under EBUS guidance.
Transbronchial Biopsy (TBB):
EBUS plays a crucial role in assisting transbronchial biopsy of peripheral intrapulmonary lesions, addressing challenges such as radiation exposure and variable diagnostic yields associated with conventional methods like fluoroscopy-guided TBB or CT-guided percutaneous needle aspiration cytology. By leveraging the reflective properties of lung parenchyma, EBUS allows precise localization of pulmonary masses, even those not visible on fluoroscopy.
Pulmonary lesions exhibit distinctive hypoechoic textures and well-defined borders on EBUS due to the strong reflective interface between aerated lung tissue and the lesion. A classification system based on internal lesion structures aids in distinguishing benign from malignant lesions.
Recent advancements, such as a guided sheath, have further improved the diagnostic yield of TBB under EBUS guidance. This technique involves introducing a miniature probe into the guided sheath, inserted into the bronchoscope’s working channel. After lesion localization with EBUS, biopsy forceps, and a bronchial brush are used for pathological and cytological examinations. Surprisingly, the diagnostic yield of this method remains consistent regardless of tumor size.
Peripheral Pulmonary Lesions:
Historically, CT-guided needle aspiration, surgical lung biopsy, or video-assisted thoracoscopic surgery were preferred procedures for peripheral pulmonary lesions (PPL) assessment. However, these surgical interventions are invasive, requiring general anesthesia and hospitalization, while CT-guided procedures pose risks of pneumothorax and radiation exposure, with pneumothorax incidence ranging from nine to 64 percent.
A comparative study between CT-guided biopsy and radial probe EBUS-guided biopsy revealed similar diagnostic accuracy but significantly lower pneumothorax incidence in the radial probe EBUS group. The initial series of radial probe EBUS included PPL patients who underwent transbronchial lung biopsy under fluoroscopic and radial EBUS guidance, demonstrating comparable diagnostic accuracy. However, radial EBUS showed a trend towards better yield in lesions less than three centimeters. Subsequent studies utilizing the guide-sheath method achieved diagnostic accuracy, unaffected by fluoroscopy.
Studies assessing radial EBUS for diagnosing PPLs indicate that its diagnostic yield remains consistent regardless of fluoroscopy. Factors such as the air bronchus sign in chest CT, lesion size and location, probe position, and echogenicity influence the diagnostic yield of radial EBUS without fluoroscopy.
Combining radial EBUS with a guided sheath or rapid on-site evaluation may enhance diagnostic accuracy for challenging PPLs. While combining fluoroscopic guidance with radial EBUS may seem beneficial, its limitations include difficulty in visualizing smaller lesions, radiation exposure, and high costs, which suggest radial EBUS without fluoroscopy is a safe alternative with a low risk of pneumothorax.
Conclusion:
Radial-probe EBUS presents a favorable safety profile, minimal complications, and heightened sensitivity in diagnosing peripheral pulmonary lesions, lung cancer, and mediastinal tumors. It represents a novel advancement, offering bronchoscopists expanded visualization capabilities beyond conventional methods. With its ability to provide high-resolution imaging of bronchial wall structures and surrounding tissues, the radial probe EBUS enhances diagnostic accuracy. This minimally invasive procedure ensures safety and offers a high rate of accurate diagnosis.
