Endobronchial ultrasound: Technical aspects

INTRODUCTION — Endobronchial ultrasound (EBUS) is a bronchoscopic technique that uses ultrasound to visualize structures within and around the airway wall as well as the lung [1,2]. EBUS is different than endoscopic ultrasound (EUS). While both visualize and guide sampling of mediastinal lymph nodes, EBUS is performed during bronchoscopy and EUS is performed during gastrointestinal endoscopy. (See "Endoscopic ultrasound-guided sampling of the mediastinum: Technique, indications, contraindications, and complications".)

Types of EBUS and EBUS-guided sampling techniques are discussed in this topic review. The indications, contraindications, and complications of EBUS as well as the indications for EUS are discussed separately. (See "Endobronchial ultrasound: Indications, contraindications, and complications" and "Endoscopic ultrasound-guided fine needle aspiration in the gastrointestinal tract".)

ADVANTAGES AND DISADVANTAGES — The main advantage of EBUS guided sampling is that compared with surgical sampling, EBUS is a minimally invasive procedure that can be performed using local anesthesia and moderate sedation. In addition, EBUS can access a wide range of mediastinal lymph nodes as well as hilar lymph nodes (2R, 2L, 3p, 4R, 4L, 7, 10R, 10L, 11R, 11L) (figure 1 and figure 2) and sample centrally located pulmonary lesions with high sensitivity. (See "Endobronchial ultrasound: Indications, contraindications, and complications", section on 'Indications'.)

EBUS cannot, however, image or sample subaortic (stations 5 and 6) and paraesophageal (station 8) lymph nodes. Its availability is institution-specific, and expertise is required to interpret images and obtain diagnostic samples. In addition, the negative predictive value (NPV) is not as high as surgical sampling, such that a negative sample may necessitate the acquisition of tissue using an alternative modality (eg, surgical biopsy, mediastinoscopy). Additional limitations associated with EBUS-guided transbronchial needle aspiration (TBNA) that may contribute to the low NPV of EBUS (eg, small sample size) are discussed separately. (See "Procedures for tissue biopsy in patients with suspected non-small cell lung cancer", section on 'Limitations'.)

TYPES OF EBUS — Two types of EBUS exist: radial probe EBUS (RP-EBUS) and convex probe EBUS (CP-EBUS).

Radial probe EBUS — RP-EBUS provides high definition, 360-degree images of the airway wall and surrounding structures (image 1). RP-EBUS is used for visualization of peripheral lung nodules and assists bronchoscopists during transbronchial biopsies. The major advantage of RP-EBUS, compared with CP-EBUS, is its ability to visualize the layers of the airway wall in greater detail. However, RP-EBUS does not permit sampling in real-time such that sequential sampling with separate equipment is necessary. (See 'Sampling technique' below.)

Technique — RP-EBUS is performed by placing the tip of a conventional bronchoscope in the area of interest, inserting the radial ultrasound probe through the working channel of the bronchoscope, and inflating a balloon sheath with water. Three radial ultrasound probes are available:

●Central airway radial probes:

•The 20 MHz miniature radial probe is the standard radial probe (picture 1). It is inserted through the 2.8 mm working channel of a bronchoscope and can extend into the subsegmental bronchi. The probe has a resolution of less than 1 mm and a penetration of 5 cm [2,3].

•The 30 MHz miniature radial probe is similar to its 20 MHz counterpart but provides a more detailed image of the airway wall and surrounding structures [4].

●Peripheral radial probe:

•The 20 MHz ultra-miniature radial probe is smaller than either of the central airway radial probes (picture 2). It can be inserted through a 2 mm working channel of a bronchoscope and can extend further into subsegmental bronchi than the miniature radial probe. This allows peripheral intrapulmonary nodules to be visualized. (See "Endobronchial ultrasound: Indications, contraindications, and complications", section on 'Sampling parenchymal pulmonary nodules'.)

Convex probe EBUS — CP-EBUS provides a view that is parallel to the shaft of the bronchoscope; the angle of view is 90 degrees and the direction of view is 35 degrees forward oblique (image 2), although the angle and direction varies with different CP-EBUS equipment. Color flow and Doppler features permit identification of vascular and cystic structures. The major advantage of CP-EBUS is its ability to guide real-time sampling.

Technique — EBUS-guided transbronchial needle aspiration (EBUS-TBNA) is performed using the CP-EBUS equipped with a convex ultrasound probe attached on the tip. The tip of the CP-EBUS is placed adjacent to the area of interest, and the balloon attached on the probe is inflated with saline to improve acoustic coupling (picture 3). Both the ultrasound image and plain-view endoscopic image are displayed on the same monitor. The ultrasound image can be frozen, allowing the size of lesions to be measured in two dimensions.

SAMPLING TECHNIQUE — EBUS can be used to guide bronchoscopic sampling of lymph nodes (mediastinal and hilar) and parenchymal pulmonary nodules (central and peripheral) [5-9].

Lymph nodes — Real-time EBUS-guided transbronchial needle aspiration (EBUS-TBNA) of mediastinal and hilar lymph nodes can be performed using convex probe EBUS (CP-EBUS) (table 1). With the emergence of CP-EBUS, radial probe EBUS (RP-EBUS)-guided TBNA is rarely being used for sampling of the lymph nodes.

Real-time TBNA with CP-EBUS — Real-time TBNA refers to simultaneous visualization and sampling. It is performed using CP-EBUS, which is used to identify the target lymph node. TBNA technique, including sample preparation, is described separately. (See "Bronchoscopy: Transbronchial needle aspiration", section on 'Technical considerations'.)

In brief, a transbronchial needle system (a flexible catheter that contains a 21 or 22 gauge retractable sharp beveled needle with a stylet) is inserted through the working channel of the bronchoscope and advanced until the catheter emerges from the bronchoscope, just proximal to the ultrasound probe (picture 3). Once the catheter emerges from the bronchoscope, an image of the target is acquired, and the needle is then pushed through the bronchial wall and into the target lymph node under direct ultrasound visualization (image 2). Suction is applied using a 20 mL syringe while the catheter is agitated. Suction is released and the needle is pulled into the flexible catheter. The entire transbronchial needle system is then removed from the bronchoscope. The aspirated specimen is removed from the needle lumen and processed for cytologic and/or histologic analysis (picture 4).

Sequential TBNA with RP-EBUS — Sequential sampling refers to localization of the target lymph node as the first step, followed by TBNA as the second step. A standard flexible bronchoscope is used for RP-EBUS-guided TBNA. Initially, the RP-EBUS is inserted through the channel of the flexible bronchoscope to visualize the lymph node. After confirmation of the lymph node, the RP-EBUS is removed from the channel. Finally, the TBNA needle is inserted through the channel and TBNA is performed in a standard fashion, targeting the lymph node based on the initial assessment with the RP-EBUS. (See "Bronchoscopy: Transbronchial needle aspiration", section on 'Technical considerations'.)

Parenchymal lesions — Large centrally located lesions adjacent to major airways can be sampled by EBUS-TBNA using the CP-EBUS. On the other hand, peripheral lung nodules are out of the reach of the CP-EBUS; thus the RP-EBUS-guided biopsy can be used to assist sampling.

CP-EBUS-TBNA — For central lesions that are close to the airway, CP-EBUS is used to guide TBNA sampling under direct visualization using a similar approach to that described for lymph nodes above. (See 'Real-time TBNA with CP-EBUS' above.)

RP-EBUS-guided transbronchial biopsy — For nodules that are located peripherally, sequential sampling with RP-EBUS guidance increases the yield of transbronchial biopsy. During this procedure, the guide sheath can assist the bronchoscopist to guide the biopsy needle, forceps, and brush to the lesion of interest after confirmation of the lesion with the RP-EBUS. In addition, compared with transbronchial biopsy using standard bronchoscopy without ultrasound guidance (ie, "blind" sampling), RP-EBUS allows confirmation of the position of the peripheral nodule, which likely increases the diagnostic yield.

●RP-EBUS-guided transbronchial biopsy using the guide-sheath is performed first by navigating the bronchoscope tip into the bronchus nearest the nodule. A navigation system can be used to guide the bronchoscope to the nodule or, if a navigation system is not used, a metal curette is available on some probes to steer the sheath under fluoroscopic guidance. The use of RP-EBUS probe using a navigation system is discussed separately. (See "Image-guided bronchoscopy for biopsy of peripheral pulmonary lesions", section on 'Radial probe endobronchial ultrasound (RP-EBUS)'.)

●The ultra-miniature radial probe is placed in a guide sheath. Both the probe and guide sheath are advanced through the working channel of the bronchoscope until the nodule is visualized (image 3 and figure 3). (see 'Radial probe EBUS' above)

●The radial probe is removed, leaving the guide sheath in position. A biopsy needle, forceps, or a bronchial brush is inserted through the guide sheath and into the nodule, and a sample is taken (figure 3). (See "Flexible bronchoscopy in adults: Associated diagnostic and therapeutic procedures", section on 'Diagnostic'.)

Use of a guide sheath improves the likelihood that a sample will be diagnostic [6,10-13]. Use of RP-EBUS-guided biopsy and navigation techniques to biopsy peripheral pulmonary lesions is discussed separately. (See "Image-guided bronchoscopy for biopsy of peripheral pulmonary lesions", section on 'Radial probe endobronchial ultrasound (RP-EBUS)'.)

FOLLOW-UP — Convex probe EBUS (CP-EBUS)-guided sampling of lymph nodes is one of the safest bronchoscopic procedures. Complications, however, have been reported including pneumothorax, pneumomediastinum, bleeding, and retained foreign body. A chest radiograph should be performed following radial probe EBUS (RP-EBUS) guided transbronchial biopsy to evaluate for complications, such as pneumothorax, and occasionally following CP- or RP-EBUS-transbronchial needle aspiration (TBNA) of mediastinal or hilar lymph nodes if complications are suspected (eg, pneumothorax or pneumomediastinum). (See "Endobronchial ultrasound: Indications, contraindications, and complications", section on 'Complications'.)

SUMMARY AND RECOMMENDATIONS

●Endobronchial ultrasound (EBUS) is a bronchoscopic technique that uses ultrasound to visualize structures within and around the airway wall, lung, and mediastinum. EBUS is a minimally invasive, procedure that can be performed on an outpatient basis using local anesthesia and conscious sedation. (See 'Advantages and disadvantages' above.)

●Two types of EBUS exist: radial probe EBUS (RP-EBUS) and convex probe EBUS (CP-EBUS). RP-EBUS provides high definition, 360-degree images of the airway wall and surrounding structures in great detail (image 1). CP-EBUS shows the same structures in a plane parallel to the shaft of the bronchoscope (image 2). The major advantage of CP-EBUS is its ability to guide sampling real-time. In contrast, RP-EBUS does not permit sampling in real-time such that sequential sampling is necessary. (See 'Types of EBUS' above.)

●EBUS can be used to guide bronchoscopic sampling of lymph nodes (mediastinal and hilar) and of parenchymal pulmonary nodules (central and peripheral). EBUS-guided transbronchial needle aspiration (EBUS-TBNA) can be used to sample mediastinal and hilar lymph nodes and centrally located pulmonary nodules or masses. RP-EBUS-guided transbronchial biopsy and bronchial brushing of peripheral pulmonary nodules can be performed using RP-EBUS. (See 'Sampling technique' above.)

●A chest radiograph should be performed following RP-EBUS-guided transbronchial biopsy to evaluate for complications, such as pneumothorax, and occasionally following CP- or RP-EBUS-TBNA of mediastinal or hilar lymph nodes if complications are suspected (eg, pneumomediastinum). (See 'Follow-up' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Takehiko Fujisawa, MD, PhD, who contributed to earlier versions of this topic review.