Systematic Endobronchial Ultrasound - The Six Landmarks Approach

Summary

Endobronchial ultrasound-guided sampling using transbronchial needle aspiration plays a key role in staging and diagnosing lung cancer. We propose a systematic stepwise approach dividing the procedure into six landmarks that should be taught to new operators.

Abstract

Lung cancer is the leading cause of cancer mortality globally. To ensure the correct diagnosis and staging in relation to treatment options, it is crucial to obtain valid biopsies from suspected tumors and mediastinal lymph nodes and accurate identification of the mediastinal lymph nodes regarding the Tumor-Node-Metastasis (TNM)-classification. Flexible bronchoscopy combined with endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) is essential in the workup and diagnosis of patients suspected of lung cancer. EBUS-TBNA from mediastinal lymph nodes is a technically difficult procedure and has been identified as one of the most important procedures that should be integrated into a simulation-based training program for invasive pulmonologists. More specific guidelines that govern training in EBUS-TBNA are needed to meet this demand. We hereby propose a systematic, stepwise approach with specific attention to six landmarks that support the endoscopist when navigating through the bronchial maze. The stepwise approach relying on the six landmarks is used in the EBUS-certified training program offered by the European Respiratory Society (ERS).

Introduction

Lung cancer is one of the most common cancers worldwide with 2.21 million cases in 2020, and the most frequent cause of cancer death with 1.80 million deaths in 2020¹. As with most cancers, fast and accurate diagnosis of lung cancer is crucial to be able to offer the best treatment, which in cases with a localized disease with no or little spreading to mediastinal lymph nodes can be surgical removal of the tumor. In order to be able to confirm or invalidate the suspicion of malignancy and to determine the Tumor-Node-Metastasis (TNM)-classification if lung cancer is confirmed², it is extremely important to have good and representative biopsies from the suspected tumor or lymph nodes.

Among the invasive techniques, flexible bronchoscopy combined with endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) plays a key role³. However, it is a complex technical procedure, and the success is dependent on the competence of the operator⁴. Anatomic orientation can easily be lost if the endoscopist does not know the anatomy of the mediastinum. Knowledge of endosonographic anatomy and its relation to the TNM lung cancer classification system is therefore crucial. In the case of lung cancer, if no tumor cells are found in any lymph node stations, the disease is classified as N0 disease and is often operable and thus, potentially curable. In the case of a right-sided lung tumor, the disease is classified as N1 disease if tumor cells are solely found in station 10R and could be operable and thus potentially curable. However, if tumor cells are found in station 4R, the disease is classified as N2 disease, and the patient can only be offered life-prolonging chemotherapy⁵. Three borders should therefore be remembered as they are important for treatment and prognosis.

(i)The left border of the trachea is the border between stations 4R and 4L.
(ii)The upper border of the left pulmonary artery is the border between stations 4L and 10L.
(iii)The lower border of the azygos vein is the border between stations 4R and 10R⁶.

To be qualified to perform EBUS-TBNA in the diagnostic process of possible lung cancer, it is therefore essential that EBUS-TBNA is thoroughly trained in a simulator-based setting based on a structured training curriculum before being performed on patients. Therefore, a stepwise approach relying on the six anatomical landmarks is used in the EBUS-certified training program offered by the European Respiratory Society (ERS)⁷.

We demonstrate the stepwise structured guide in a simulation-based setting at Copenhagen Academy for Medical Education and Simulation (CAMES), Denmark⁸, on how to perform EBUS-TBNA with the EBUS endoscope relying on the six anatomical landmarks⁹ as a guide.

Protocol

This study uses the EVIS Exera II endoscopy tower with a BF-UC180F EBUS endoscope (Figure 1) to demonstrate the scope and the Surgical Science Simulator (ENDO mentor suite) with the GI-Bronch Mentor software from Simbionix, Essential EBUS Case 6, when performing the EBUS procedure in the simulation-based setting. No patients are included in the study as the entire procedure is performed on the Surgical Science Simulator (ENDO mentor suite). Prior to the EBUS procedure, a complete bronchoscopy is performed using a regular bronchoscope to make sure the bronchial tree has been visualized systematically and to identify key anatomical positions where the underlying lymph node stations must be located (Figure 2).

1. Handling of the endoscope

NOTE: The EBUS endoscope is handled similarly to the bronchoscope. However, it is important to note that contrary to the bronchoscope, the EBUS endoscope gives an oblique angle view as the ultrasound transducer reduces the visibility (Figure 3).

1. Hold the endoscope in the left hand with the left thumb on the steering lever.
2. Hold the distal end of the endoscope in the right hand and enter the trachea through the nasal or oral cavity. When the vocal cords are visualized at the bottom of the picture (Figure 3B), administer 2 mL of 2% lidocaine twice via the simulator by pressing the appropriate button on the screen, and pass the vocal cords with care.
3. Administer a further 2 mL of 2% lidocaine in the trachea as well as in the right and left main bronchus, respectively.

2. Anatomy

1. After having inspected the bronchial tree, retract the bronchoscope and change to the EBUS scope. Turn on the ultrasound transducer and locate the six anatomical EBUS landmarks in the order mentioned below.
   1. Locate Landmark 1 = station 4L
      1. Locate station 4L at the left side of the trachea, just cranial to the carina. To find station 4L, turn the endoscope counterclockwise in the trachea and locate it between the arch of the aorta and the left pulmonary artery, sometimes referred to as "the Mickey Mouse window" (Figure 4).
   2. Locate Landmark 2 = Station 7
      1. Locate station 7 between the right pulmonary artery and the left atrium below the carina. Place the EBUS scope in the right or the left main bronchus and turn the endoscope facing medially (Figure 5).
   3. Locate Landmark 3 = Station 10L
      1. Locate station 10L adjacent to the left main bronchus cranial to the left upper lobe. Place the endoscope in the left main bronchus or the left upper lobe and look upwards. The upper border of the left pulmonary artery forms the boundary between stations 4L and 10L (Figure 6).
   4. Locate Landmark 4 = Station 10R
      1. Locate station 10R on the lateral wall of the right main bronchus, just caudal to the inferior border of the azygos vein. The upper border is the lower border of the azygos vein. Place the endoscope in the right main bronchus or the right upper lobe bronchus and look upwards (Figure 7).
   5. Locate Landmark 5 = The azygos vein
      1. To find the azygos vein, retract the endoscope slightly cranially and turn the transducer clockwise in the trachea. Turn the transducer counterclockwise to visualize the azygos vein draining into the superior vena cava (Figure 8).
   6. Locate Landmark 6 = Station 4R
      1. To find station 4R, retract the endoscope further cranially from the azygos vein and turn the transducer clockwise in the trachea. Locate station 4R to the right or in front of the trachea above the lower border of the azygos vein, which marks the border between station 10R and 4R (Figure 9).
2. After having located the six landmarks, look for other lymph node stations, i.e., stations 2R, 2L, 11R, and 11L, and other structures of clinical importance. At least stations 4L, 7, and 4R should be biopsied³.
3. When the relevant lymph node is localized, ask the assistant for the biopsy equipment. The biopsy equipment includes a sheath protecting the needle, connected to a handle that can be locked onto the endoscope. Inside the sheath is the needle, and inside the needle is the stylet. When inserting the needle into the working channel, keep the steering lever in a neutral position as shown in the video to avoid damage to the endoscope.
   NOTE: The needle used here comes with the simulator. However, the recommended needle size for this procedure is 21 G.
4. Adjust the sheath so it is visible at the end of the endoscope; however, no more than 1-2 mm.
5. Turn the transducer towards the bronchial wall so the lymph node is visualized on the left side of the ultrasound picture. Now, perform the biopsy.
6. After puncturing the lymph node with the needle, ask the assistant to remove the stylet and then apply suction to the needle by pressing the appropriate button on the screen. The needle must be moved back and forward several times.
7. Remove the suction and retract the needle tip while inside the sheath. Ensure that the distal end of the endoscope is not flexed and remains in a neutral position to prevent damage to the endoscope. Each lymph node must be punctured at least three times^10,11.
8. After the final biopsy, check for bleeding. Inspect the place for biopsy with the white light view and stay for a few seconds. If no bleeding is observed, retract the endoscope.

Results

The above-mentioned structured approach to an EBUS-TBNA procedure has been taught at CAMES since 2016 as part of the EBUS-certified training program offered by the European Respiratory Society (ERS)⁷. The 6 landmarks approach is based on a validated assessment tool for measuring competency in EBUS-guided transbronchial needle aspiration⁴. By performing EBUS-TBNA in a structured way, as shown above, no important lymph nodes will be missed, and the diagnostic accuracy will be...

Discussion

We hereby propose a systematic approach to the EBUS-TBNA procedure by splitting the anatomy into six landmarks to help guide the endoscopist through the bronchial maze. Furthermore, we demonstrate how to perform needle aspiration in a systematic way possible to repeat every time to standardize the procedure.

Even though the simulation-based setting is a safe environment, the endoscopist should be aware of some critical steps in the procedure. Initially, it is important to know the oblique angl...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
EVIS Exera II endoscopy tower with a BF-UC180F EBUS endoscope	Olympus	https://medical.olympusamerica.com/products/bf-uc180f-ebus-bronchoscope
ENDO mentor suite	Surgical Science	https://simbionix.com/endo-mentor-suite/	Surgical Science Simulator
GI-Bronch Mentor software	Simbionix	https://simbionix.com/simulators/gi-mentor/