Drs. Ogita, Robbins, Blum, and Harris have reviewed the various invasive and noninvasive staging modalities used for the staging of patients with non-small-cell lung cancer (NSCLC). The authors represent the specialties of oncology, gastroenterology, and thoracic surgery at a major medical center. The accuracy of noninvasive staging via computed tomography (CT) and positron-emission tomography (PET) scanning is reviewed using a retrospective review of a large number of published series. Additional attention is focused on the results of more invasive procedures, including mediastinoscopy, endoscopic ultrasound fine-needle aspiration (EUS-FNA), and endobronchial ultrasound FNA (EBUS-FNA). Astute readers may wonder why a gastroenterologist would be writing about lung cancer staging and why a gastroenterologist would be writing this editorial.
Gastroenterologists are the major source of controversy in lung cancer staging. The performance of EUS-FNA by gastroenterologists has demonstrated an accuracy rate superior to any other staging modality in lung cancer. How could an endoscopic procedure designed for the upper GI tract have such success in the staging of lung cancer? Let's examine some of the key features of EUS-FNA.
Origins of EUS
EUS was initially designed to provide an imaging modality for the staging of esophageal and gastric cancer. In the original configuration of the device, a high-frequency ultrasound probe was placed on the tip of an endoscope. High-resolution, cross-sectional images were obtained of the relationship between the malignant mass and the wall of the esophagus or stomach. Intramural lesions (T1-2) were found to be localized to the wall, whereas transmural lesions (T3-4) were found to be invading through the muscularis propria.
Not only did EUS provide highly accurate tumor staging, EUS also provided detailed imaging of mediastinal lymph nodes. In the traditional radial EUS configuration, only imaging of lymph nodes was possible. With the recent introduction of linear EUS, FNA has become standard and has dramatically improved the accuracy of lymph node staging.
Principles of EUS-FNA
EUS-FNA has dramatically increased the accuracy of esophageal cancer staging through lymph node aspiration. What are the principles used in the aspiration of lymph nodes? The first principle of EUS-FNA is the safety of the procedure. When small-gauge needles (22 or 25 gauge) are placed across the esophagus, the rate of complications (such as bleeding, infection, pneumomediastinum) is surprisingly rare. The esophagus (and the rest of the GI tract) has proven to be a remarkable window for FNA. The small tracts made by the passage of the needle are quick to close and seal over completely. Bleeding is rare because the endoscopist is able to guide the needle very accurately with Doppler imaging and avoid blood vessels.
The second principle of EUS-FNA is the high quality of aspiration cytology. Despite the needle passing through the echoendoscope, into the esophageal lumen, and across the esophageal wall, the quality of cytology of the aspirated lymph node is relatively high. There are several key characteristics of EUS-FNA that assure high-quality cytology. Most importantly, the aspiration needle is occluded by a stylet when it is passed through the esophageal wall, preventing the passage of gastroesophageal mucosal material into the needle. Aspiration of lymph nodes provides highly recognizable cytologic material for the cytologist. It is rare for gastroesophageal contamination to cause falsely negative or positive cytology.
The third principle of EUS-FNA is the least secured one. Although EUS imaging readily detects lymph nodes along the esophagus (for distances up to 5 cm) and it is technically easy, there is some uncertainty as to how well aspiration cytology detects malignancy. In the original studies of a large spectrum of patients with mediastinal lymphadenopathy, the accuracy of EUS-FNA was 94% in the detection of malignancy in enlarged lymph nodes. In the staging of esophageal cancer, the accuracy of EUS-FNA for detecting malignancy in celiac lymph nodes has proven to be highly sensitive (90%). Aspiration cytology is dependent upon the ability of the cytologist to recognize malignant cells within lymphocytes.
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