Pulmonary Medicine

Interventional Bronchoscopy: Endobronchial Ultrasound

General description of procedure, equipment, technique

Endobronchial Ultrasound

Endobronchial ultrasound (EBUS) is a bronchoscopic technique that uses ultrasound to visualize structures adjacent to the central airways (linear EBUS) and lung parenchyma (radial probe EBUS). It also enables real-time image-guided transbronchial needle aspiration (TBNA) of mediastinal and hilar lymph nodes.

EBUS is different from endoscopic ultrasound (EUS); while both techniques permit imaging and guided sampling of mediastinal lymph nodes, EBUS is performed during bronchoscopy, while EUS is performed during upper gastrointestinal endoscopy.

Indications and patient selection

EBUS is used to guide bronchoscopic sampling of mediastinal lymph nodes, hilar lymph nodes, and peripheral pulmonary nodules.

Contraindications

A contraindication is when no lymph node is visualized. Relative contraindications include: systemic anticoagulation, intervening vessels between ultrasound probe and target lesion.

Details of how the procedure is performed

Radial Probe EBUS (RP-EBUS) provides 360-degree images of the airway wall and surrounding structures and visualization of the layers of the airway wall. RP-EBUS is performed by placing the bronchoscope tip in the area of interest, inserting the radial ultrasound probe through the working channel, and performing ultrasonographic examination. 20 MHz or 30 MHz miniature radial probes provide a depth of penetration of 5 mm. An ultra-miniature radial probe may be extended into subsegmental bronchi, allowing visualization of peripheral intrapulmonary nodules.

Biopsy of peripheral lung nodules via ultra-miniature radial probe guidance is performed one of two ways. One approach is to place a guide sheath into or proximal to the lesion. The probe and guide sheath are advanced through the working channel of the bronchoscope until the nodule is visible. The radial probe is removed, leaving the guide sheath in position. A biopsy forceps, bronchial brush, or needle is then inserted through the guide sheath and the nodule sampled.

The other approach is with the use of fluoroscopy, with or without a guide sheath. This method requires that the nodule or ground-glass opacity (GGO) is visible on chest x-ray. The nodule can be located with a combination of fluoroscopy and the ultrasound probe. Once the lesion is identified based on these two modalities, the bronchoscopist can retrace the segmental pathway to the lesion with the white-light scope and confirm the location with fluoroscopy. A biopsy forceps or bronchial brush can then be used at that location to sample the lesion.

Convex Probe EBUS (CP-EBUS) provides a view that is parallel to the shaft of the bronchoscope. Color flow and Doppler features permit identification of vascular and cystic structures, thus enabling real-time TBNA. The procedure is performed using a 7.5 MHz convex ultrasound probe attached to the bronchoscope's tip. Inflating the balloon sheath with water may allow for improved apposition with the tracheobronchial wall, which may facilitate visualization and TBNA. The ultrasound image and conventional bronchoscopy image may be displayed on the same monitor, and EBUS-guided TBNA of mediastinal and hilar lymph nodes may be performed real-time.

A transbronchial needle system contains a 19, 21, 22 or 25-gauge, retractable, sharp, beveled needle with an internal sheath that is inserted through the working channel, just proximal to the ultrasound probe. The scope should be in a neutral position as the needle is passed through its working channel to avoid injury to the EBUS bronchoscope. Once the catheter/sheath emerges from the bronchoscope, the needle is advanced from the catheter, locked into position, and then pushed through the bronchial wall into the target under direct ultrasound visualization. TBNA can be performed with or without suction, depending on the operator’s preference and the specific indication. Suction can often increase the yield; however, it can also result in a bloody sample which may reduce the diagnostic efficiency of Rapid On-Site Evaluation (ROSE) of cytology. Suction is applied from a syringe, and the needle slowly agitated. When suction is released, the needle is pulled into the flexible catheter.

Interpretation of results

EBUS is useful in staging the nodal component in lung cancer. Once enlarged mediastinal lymph nodes are identified by CT scan or are identified as metabolically active on PET, lymph node sampling facilitates evaluation since the sensitivity and specificity of imaging alone in the detection of lymph node metastasis are inadequate and similar to TBNA.

A clinical trial of RP-EBUS in patients with suspected lung cancer demonstrated that RP-EBUS-guided TBNA was more sensitive than TBNA alone (84% versus 58%, respectively); no difference was found between the two procedures with regard to subcarinal lymph node sampling. Multiple studies since that time have confirmed these findings.

Another study demonstrated the proof-of-principle that CP-EBUS-guided TBNA successfully samples mediastinal or hilar lymph nodes in patients with known or suspected non-small cell lung cancer (NSCLC). Malignancy was detected with a sensitivity of 95 percent, a specificity of 100 percent, and diagnostic accuracy of 96 percent. A large meta-analysis of eleven studies showed similar sensitivity and specificity for the technique.

A combination of EBUS-guided TBNA and EUS-FNA may make the entire mediastinum accessible to node sampling, thereby decreasing the need for more invasive procedures. The combination appears to improve the diagnostic yield when compared to either procedure alone. The most recent guidelines for the staging of lung cancer (published jointly by the European Society of Thoracic Surgeons, European Respiratory Society and the European Society of Gastrointestinal Endoscopy) provide a Grade A recommendation that endoscopic staging of lung cancer with EBUS + EUS should be the initial procedure rather than surgical mediastinal staging (i.e., cervical mediastinoscopy, anterior mediastinotomy).

RP-EBUS-guided TBNA is useful in performing biopsies of peripheral pulmonary nodules. In a large, randomized trial in which patients were assigned to RP-EBUS-guided or conventional transbronchial biopsy, evaluation of nodules that were smaller than 3 cm demonstrated that RP-EBUS-guided transbronchial biopsy identified malignant disease with a sensitivity of 75 percent and accuracy of 83 percent, while conventional transbronchial biopsy identified malignant disease with a sensitivity 31 percent and an accuracy of 50 percent. However, the diagnostic yield with RP-EBUS-guided TBNA is lower than that of CT-guided percutaneous transthoracic needle aspiration for larger lesions. Therefore, RP-EBUS TBNA provides an advantage only if the lesion is smaller than 3 cm or if the lesion is felt to be too deep for CT-guided percutaneous transthoracic needle biopsy.

CP-EBUS-TBNA allows real-time sampling of mediastinal lesions. In a randomized study of sarcoidosis, CP-EBUS-TBNA was shown to have a higher diagnostic yield (sensitivity of 83%, specificity of 83%) than conventional TBNA (sensitivity of 61%, specificity of 100%). Similarly, EBUS is an effective diagnostic method in the diagnosis of lymphoma. However, the diagnostic accuracy of EBUS when compared to the gold standard of cervical mediastinoscopy is not as good for diagnosing lymphoma and sarcoidosis as it is for diagnosing solid malignancies.

EBUS does have some disadvantages that standard fiberoptic (i.e. white light) bronchoscopy does not have. The bronchoscope used is larger than a conventional one, it provides poorer image quality, and its use requires additional training.

Performance characteristics of the procedure (applies only to diagnostic procedures)

Many studies have assessed and reported the test characteristics of EBUS invasive mediastinal staging of lung cancer. Systematic reviews suggest a pooled sensitivity of 94% in patients with abnormal mediastinum on CT or PET. Among all patients (including those with normal mediastinum), the pooled sensitivity is 80%, ranging from sensitivities of 46% to 92% depending on the study. This variability is a function of both skill/expertise as well as local prevalence of positive mediastinal disease. Specificity is almost always 100%.

Outcomes (applies only to therapeutic procedures)

Not applicable

Alternative and/or additional procedures to consider

Alternative procedures to consider are surgical or endoscopic options. Endoscopic options are limited to Esophageal Ultrasound (EUS). Studies have shown that sensitivity of invasive mediastinal staging is increased when a combination of EBUS and EUS are used. Surgical options include mediastinoscopy (direct or video-assisted), anterior mediastinotomy, video-assisted thoracic surgery, video-assisted mediastinal lymphadenectomy (VAMLA), or transcervical extended mediastinal lymphadenectomy (TEMLA).

Complications and their management

The addition of EBUS in performing TBNA does not add to the complication rate, which is similar to that seen with conventional TBNA (if not slightly safer). A recent systematic review of 16 181 patients undergoing EBUS and EUS reported a pooled adverse event rate of 0.05% for EBUS. The majority (>55%) of complications are self-limited bleeding complications, the management of these does not require much more than the usual topical means of hemostasis (i.e. tranexamic acid, epinephrine or iced saline). An additional modality of hemorrhage control utilizes the EBUS balloon to provide pressure on the tracheal/bronchial wall and thus tamponade bleeding.

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