How to find the limit between station 2 and station 4 during mediastinoscopy?

During mediastinoscopy, the definition of the limit between station 2 and station 4 is arbitrary. We describe a simple technique based on computed tomographic scan evaluation to precisely define it. The technique is based on calculating the distance between the sternal notch and the upper aortic arch on computed tomographic scan (radiological station 2 lower limit), and subtracting a constant factor (at our institution, 20 mm) to compensate for modifications of mediastinal structures due to neck hyperextension during mediastinoscopy. This corrected distance (surgical station 2 lower limit) is labeled on the mediastinoscope. When the mediastinoscope is inserted to this distance with a lateral deviation of about 45 degrees, the point of contact with the mediastinum of the biopsy forceps is the limit between station 2 and station 4. We applied this technique in 15 consecutive patients submitted to video-assisted mediastinoscopy for lung cancer. The R2 lower limit was identified by positioning 2 surgical clips during mediastinoscopy. The position of the clips, verified by a chest roentgenogram, was excellent (on the upper aortic arch line) in 7 patients, good (at less than 5 mm from the line) in 6 patients, and acceptable (at 7 mm from the line) in 1 patient. In one case clips were not visible. The proposed technique is simple and precise. Due to the possible differences in patient positioning during mediastinoscopy in other institutions, this correcting factor (-20 mm) should be verified before using this technique to define the lower limit of station 2.