Comparison of Endobronchial Ultrasound, Positron Emission Tomography, and CT for Lymph Node Staging of Lung Cancer: Conclusion
In our study, we did not evaluate other possible methods available for obtaining samples from the mediastinal lymph nodes such as TBNA, EUS-FNA, and mediastinoscopy. However, it is hard to compare these techniques because of the difference of potential to assess different portions of the mediastinum (Fig 4). Conventional TBNA can be performed during bronchoscopy, which is usually performed in lung cancer patients avoiding separate staging pro-cedures. This is a big advantage, as in EBUS-TBNA. Conventional TBNA has same access to lymph nodes as does EBUS-TBNA. However, it is a blind procedure preventing target visualization, and therefore the yield for TBNA varies widely. From the results of the study by Herth et al, who compared EBUS-guided TBNA to TBNA, we speculate that EBUS-TBNA has a higher yield compared to conventional TBNA. EUS-FNA is an accurate technique for the analysis of mediastinal lymph nodes from the esophagus. Due to its high accuracy and safety, it is increasingly used for the staging of lung cancer. Although EUS-FNA has excellent access to the posterior nodes (stations 5, 7, 8, and 9), it is unable to image the anterior mediastinum where.
From the results of our study, we may create an algorithm for the evaluation of the mediastinum. Patients with an abnormal shadow suspected of lung cancer should be initially evaluated by CT. If there are enlarged lymph nodes, PET may be performed. During the diagnostic bronchoscopy, EBUS-TBNA of enlarged lymph nodes or PET-positive lymph nodes should be performed if the lymph nodes of interest are within the reach of EBUS-TBNA, ie, in the highest mediastinal, paratracheal, subcarinal, or hilar lesions. If a result from cytology is negative for malignancy, mediastinoscopy should be considered for confirmation of the absence of mediastinal involvement. If there are enlarged and/or PET-positive lymph nodes in stations 5, 8, or 9, other invasive procedures such as EUS-FNA and thoracoscopy should be considered.
In conclusion, EBUS-TBNA has a high sensitivity as well as specificity compared to CT or PET for mediastinal staging in patients with potentially resectable lung cancer. Tissue confirmation obtained by EBUS-TBNA is especially important for accurate staging. It should be considered for evaluation of the mediastinum early in the staging process of lung cancer. most of the mediastinal lymph nodes made be involved as in our current study.
One major drawback of EBUS-TBNA is its limitation to access some part of the mediastinum. Although EBUS-TBNA can sample all of the lymph node stations that are assessable by mediastinoscopy, the “gold standard” for mediastinal staging, its inability to image and access the subaortic and paraesophageal lymph nodes (stations 5, 6, 8, and 9) may become a problem. If subaortic and or paraesophageal lymph nodes are seen on CT and are positive on PET, EUS-FNA should be considered to evaluate these nodes. By combining transbronchial ultrasound-guided aspiration and EUS-FNA, the majority of the mediastinum is accessible as shown by Herth et al.
Figure 4. Sampling techniques and their diagnostic reach of mediastinal and hilar lymph node stations (1, highest mediastinal; 2, upper paratracheal; 4, lower paratracheal; 5, subaortic; 7, subcarinal; 8, paraesophageal; 9, pulmonary ligament; 10, hilar; 11, interlobar; and 12, lobar). EBUS-TBNA is performed from the airway as opposed to EUS-FNA, which is performed via the esophagus.