Ann Thorac Surg 2006;81:1150-1152
© 2006 The Society of Thoracic Surgeons
How to do it
How to Find the Limit Between Station 2 and Station 4 During Mediastinoscopy?
Francesco Leo, MD
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,
Nicolas Venissac, MD,
Daniel Pop, MD,
Sabrina Khelef, MD,
Jérôme Mouroux, MD
Thoracic Surgery Department, Nice University Hospital, Nice, France
Accepted for publication December 13, 2004.
* Address correspondence to Dr Leo, Thoracic Surgery Department, European Institute of Oncology, Via Ripamonti 435, 20100 Milan, Italy (Email: francesco.leo{at}ieo.it).
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Abstract
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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°, 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.
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Introduction
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In many lung cancer trials the involvement of the highest nodal station has been considered a marker of incomplete resection [1–2]. Given the difficulty of defining station 1 position intraoperatively, from the practical point of view, the highest lymph node station biopsied at mediastinoscopy or removed during mediastinal dissection is mediastinal station 2. For this reason the precise definition of the lower limit of station 2 is important.
Definitions of mediastinal lymph nodal stations are based on anatomical landmarks. Most of the anatomical landmarks that idenfify mediastinal lymph node stations, such as the trachea, right and left main bronchi and azygos vein, are easily identified during mediastinoscopy. The only exception is the line drawn tangential to the upper margin of the aortic arch, defining the limit between stations 2 and 4 according to the lymph node map proposed by Mountain in 1997 [3]. Therefore, during mediastinoscopy, the definition of the limit between station 2 and 4 is arbitrary.
To define the limit of nodal stations more precisely, we developed a simple technique to locate station 2 during mediastinoscopy, using a method based on assessing the distance between the sternal notch and the upper aortic arch by computed tomographic scan.
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Technique
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This technique was developed on 20 previous video mediastinoscopies by trial and error. The principle of the technique is to evaluate the position of the line dividing station 2 and 4 based on the distance between the sternal notch and the upper aortic arch observed in computed tomographic scans. This distance is measured using helical computed tomographic scan with intravenous contrast and 5-mm thick images of the mediastinum. We measure the distance between the first image of sternal manubrium and the first image of the aortic arch, and we define this distance as the radiological lower limit of station 2 (number of images x 5 mm) (Fig 1). To compensate for the neck extension due to patient position during mediastinoscopy, we then subtract 20 mm from this value to locate the surgical lower limit of station 2, and we use this corrected value to find the limit between stations 2 and 4 intraoperatively. If the radiologic limit is less than 20 mm, as in the case of severe scoliosis, the sternal notch serves as the surgical marker of the lower limit of station 2 at mediastinoscopy.
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Fig 1. The distance from the sternal notch and the upper aortic arch is assessed by computed tomographic scan. To determine the distance to apply during mediastinoscopy (the surgical station 2 lower limit) we subtract 20 mm.
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The distance defined as surgical station 2 lower limit is labeled on the upper valve of the video mediastinoscope by a strip (Fig 2). When the mediastinoscope is inserted through the cervical incision, the strip is at the level of the sternal notch and the instrument has a lateral deviation of 45°, the point of contact of the biopsy forceps with the mediastinum is the limit between station 2 and station 4.
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Fig 2. The distance defined as surgical station 2 lower limit is reported on the upper valve of the video mediastinoscope by a strip. When the mediastinoscope is inserted through the cervical incision, the strip is at the level of the sternal notch and the instrument has a lateral deviation of about 45°, the point of contact with the mediastinum of the biopsy forceps is the limit between stations 2 and 4.
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To assess the precision of the technique, we positioned two 5-mm clips at the limit between stations 2 and 4 during 15 consecutive video mediastoniscopies performed for lung cancer staging. Details on the surgical technique have been previously published [4]. The day after surgery we verified the position of the clips and their distance from the upper aortic arch line by a postero-anterior standard chest roentgenogram. The distance was expressed as a negative number if the clip was higher than the upper aortic arch line and as a positive number when it was lower. Identification of the station 2/4 limit was defined as "excellent" if the upper aortic arch line crossed the clips, as "good" if the clips were 
5 mm from it, as "acceptable" if the distance was 6–10 mm, and as "poor" if the distance was greater than 10 mm.
The study population consisted of 11 males and 4 females (mean age, 61.8; range, 46 to 75; standard deviation, 8.8). Evaluation of the clip placement was possible in 14 patients. In the remaining case the clips were not visible on postoperative chest roentgenogram.
The mean surgical station 2 lower limit was at 18.5 mm from the sternal notch (range, 0 to 35 mm; standard deviation, 9.9), and the mean distance between the clips and the upper aortic arch line was –1.35 mm (range, from –7 to 1; standard deviation, 2.27). Based on the criteria previously described, definition of the limit between stations 2 and 4 was excellent in 7 of the 14 evaluable cases (50%), good in 6 (42.8%) and acceptable in 1.
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Comment
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Following Carlens' [5] initial report in 1959, mediastinoscopy has played a central role in the mediastinal staging of lung cancer [6]. The recent introduction of video-assisted mediastinoscopy has greatly improved identification of anatomical structures such as the tracheo-bronchial angle, the azygos vein, and the left recurrent laringeal nerve [3]. The upper aortic arch line dividing station 2 from station 4 remains the only landmark difficult to recognize even during video mediastinoscopy.
In our practice the definition of station 2 has therapeutic consequences because we consider N2 patients positive at station 2 as surgical candidates after neoadjuvant treatment only when station 2 is negative at postchemotherapy positron emission tomographic scan or after a repeat mediastinoscopy.
The anatomical landmark of the lower station 2 limit depends on the lymph node map used by the surgeon. In the map proposed by Naruke and colleagues [7] and adopted by the Union Internationale Contre le Cancer, the limit is represented by the azygos vein. In the map proposed by the American Thoracic Society [8] and adopted by the North American Lung Cancer Study Group and by the American College of Surgeons Oncology Group, the limit is the line of the upper aortic arch. We considered Naruke and colleagues' [7] map to be too restrictive in the definition of station 4, and in 1997 we adopted the map proposed by Mountain and Dresler [3] and accepted by the American Joint Committee on Cancer and by the Union Internationale Contre le Cancer.
To standardize the evaluation of the station 2 position, we developed a simple technique that allows the lower limit of station 2 to be identified with a precision in the order of a few millimiters. The principle underlying the technique is that the radiologic distance assessed on computed tomograpic scan must be corrected to compensate for neck extension during mediastinoscopy.
Variability in the distance between the sternal notch and the aortic arch due to factors such as age, height, body mass index, or limited neck mobility (usually due to scoliosis) is already expressed by the radiologic distance and does not need additional correction. The correcting factor of 20 mm compensates for patient positioning (in our institution we place a roll 16 cm in diameter underneath the tips of the scapula) and should be verified on a small series of cases before routine use in other institutions.
In conclusion, the proposed technique improves the precision in defining paratracheal nodal station, resulting in more accurate mediastinal mapping and providing a reference point in case of repeat mediastinoscopy.
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Acknowledgments
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The authors thank Barbara J. Rutledge, PhD, for her editing assistance.
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References
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- Mountain CF, Dresler CM. Regional lymph node classification for lung cancer staging Chest 1997;111:1718-1723.[Abstract/Free Full Text]
- Venissac N, Alifano M, Mouroux J. Video-assisted mediastinoscopyexperience from 240 consecutive cases. Ann Thorac Surg 2003;76:208-212.[Abstract/Free Full Text]
- Carlens E. Mediastinoscopya method for inspection and tissue biopsy in the superior mediastinum. Dis Chest 1959;36:343-352.[Medline]
- Toloza EM, Harpole LH, Detterbeck F, McCrory DC. Invasive staging of non-small cell lung cancera review of the current evidence. Chest 2003;123:157-166.
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- American Thoracic Society Clinical staging of primary lung cancer Am Rev Respir Dis 1983;127:659-664.[Medline]
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Abstract
Introduction
