Comparison of Endobronchial Ultrasound, Positron Emission Tomography, and CT for Lymph Node Staging of Lung Cancer: Discussion
The result of our study for the diagnostic accuracy of thoracic CT was consistent with results from previous reports. However, the specificity of PET was lower than previously report-ed. This may be due to the fact that the study group consisted of operable lung cancer patients who usually have only small lymph nodes on CT. In fact, the median size of the lymph nodes accessed were only 12.8 X 8.7 mm in diameter, and the short axis of 40 of 147 mediastinal lymph nodes was only 5 mm. It should be noted that in our study, EBUS-TBNA correctly diagnosed each of these small lymph nodes as malignant or benign. www.medicine-against-diabetes.net
Although PET is significantly superior to CT in detecting mediastinal involvement and may be useful to detect distant metastases, inflammatory reactions of lymph nodes may lead to accumulation of FDG, resulting in false-positive results. Therefore, false-positive PET findings in the mediastinum may be frequently seen, and many authors have suggested that tissue confirmation is necessary before denial of surgery. In the present study, there were 23 false-positive findings that were all correctly diagnosed as false positive by EBUS-TBNA prior to surgery. EBUS-TBNA avoided more invasive procedures such as mediastinoscopy and video-assisted thoracic surgery. Our data support the suggestions from these authors.
FDG-PET provides biological information on tissues by evaluating glucose metabolism. Therefore, FDG uptake is not tumor specific and is often observed in inflammatory lesions and benign diseas-es. Attempts have been made to clarify the causes of false-positive PET results. Shiraki et al reported that false-positive results of FDG-PET in hilar and mediastinal lymph nodes were closely related to the size of lymph node and the volume of macrophages. Sixteen of 23 false-positive cases that we experienced were also evaluated as N2 disease by CT. The short axis of the PET hot spot lymph nodes in these patients was > 10 mm. These results suggest that enlarged mediastinal lymph nodes with FDG accumulation should be confirmed by biopsy. EBUS-TBNA allows safe and accurate cytologic evaluation that will easily differentiate the nature of the lymph nodes as shown in this study. When performing biopsy from the airway, there always remain possibilities of a false-positive result. It is safe to say that cytology and/or histology positive for malignancy is a true positive. Therefore, a false positive is usually related to a contaminant in the TBNA process. In our study, there are several lines of evidence against a contamination during the process. First of all, there were no changes in the bronchial airway at the site of puncture. Since the lymph nodes are adjacent to the bronchial wall, there is a low possibility of contamination. Secondly, the dedicated 22-gauge needle is equipped with an internal sheath that is withdrawn after the puncture of the bronchus. This sheath allows for the prevention of contamination. Collectively, it suggests that there is a low chance of contaminations during the puncture process and that there were no false-positive cases in our study. However we should always be aware of the fact that there is a chance of a false-positive EBUS-TBNA result.