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Evaluation of the Mediastinum by Invasive Techniques
Surgical Treatment of Lung Carcinoma
0039-6109/87 $0.00
+ .20
Evaluation of the Mediastinum by Invasive Techniques
Robert]. Ginsberg, M.D., F.R.C.S.(C)*
Once lung cancer has spread to mediastinal lymph nodes, the ultimate prognosis, despite complete surgical removal of the primary tumor and involved lymph nodes, is markedly worsened. This poor prognosis was recognized by many early thoracic surgeons, 1, 3 and attempts were made to identifY tumor spread to the lymph nodes of the mediastinum preoperatively, in order to avoid unnecessary thoracotomies for inoperable situations, The classic report by Daniels 6 indicated that scalene node biopsy, even in nonpalpable disease, would identifY a group of patients whose disease had spread even beyond the mediastinum to the lower reaches of the neck. Harkens and associates 8 were the first to introduce invasive staging of the mediastinum, describing a "cervical mediastinal exploration" using a Jackson laryngoscope through a cervical incision. This enabled the surgeon to palpate and directly inspect the superior mediastinum and afforded the opportunity to sample lymph nodes in that location for biopsy. Cervical mediastinoscopy as performed today was developed by Carlens 4 and popularized in North America by Pearson. 15 Exploration of the anterior mediastinum, especially in staging of left upper lobe tumors, was first advocated by McNeil and Chamberlain. 12 We have recently described the results of exploring this area of the mediastinum utilizing a standard cervical mediastinoscopy approach. 7 Transbronchoscopic needle aspiration of subcarinal lymph nodes has been used for many years in attempting to identifY involvement in this area. More recently, Wang and associates 18 have further refined this technique using a flexible bronchoscope and performing fine-needle aspiration biopsies of the subcarinal and paratracheal regions. It is claimed that N2 and N3 disease can be identified by this technique, thereby avoiding mediastinoscopy. Occasionally, exploration of the posterior mediastinum is utilized to *Surgeon-in-Chief and Head, Division of Thoracic Surgery, Mount Sinai Hospital; Professor, University of Toronto; and Consultant and Thoracic Surgeon, Princess Margaret Hospital and the Ontario Cancer Institute, Toronto, Ontario, Canada
Surgical Clinics of North America-Vol. 67, No.5, October 1987
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identify spread of lung cancer in this region, a discovery that would avoid a subsequent major thoracotomy.
INVASIVE VERSUS NONINVASIVE STAGING
Should all patients, prior to thoracotomy, undergo surgical exploration of the mediastinum to exclude the presence of inoperable N2 and N3 disease? Many argue that with the newer noninvasive (computed tomography, magnetic resonance imaging) and minimally invasive techniques (transbronchial needle aspiration biopsy), mediastinoscopy can be avoided unless results of these investigations suggest significant involvement of the mediastinum. 2,18 Mediastinoscopy, in this situation, would be used to confirm inoperability in selected cases. Others, myself included, believe that mediastinoscopy is such a safe and informative staging procedure that it should be used routinely in virtually every patient prior to thoracotomy. It avoids the 10 per cent false-negative rate inherent in all noninvasive techniques. This controversy persists and has been the subject of many articles and symposia. The results of surgery when N2 or N3 disease is resected are well known. 11, 16 Incompletely resected mediastinal nodal disease rarely, if ever, results in long-term cure, and the palliative value of such resections is questionable. Mediastinoscopy and anterior mediastinotomy will identify those patients whose tumors cannot be completely resected, by virtue of advanced N2, N3, or T4 disease. 13 It is these patients with Stage III disease who will benefit from mediastinal exploration, avoiding an unnecessary thoracotomy. Most surgeons would agree that if this type of advanced disease is identified at mediastinoscopy, no resectional surgery should be performed.
CERVICAL MEDIASTINOSCOPY
Exploration of the superior mediastinum by cervical mediastinoscopy enables the surgeon to biopsy the lymph nodes: in the anterior aspect of the subcarinal space, around the proximal main stem bronchi and lower trachea (tracheobronchial angle nodes), and in the pretracheal and paratracheal regions (Fig. 1). Complete lymph node staging of the superior mediastinum is thus possible. Technique
For adequate exposure, the patient is supine with the neck extended and the shoulders elevated by a bolster underneath. A small (3 to 4 cm) transverse incision is made 1 cm above the suprasternal notch and is carried down through platysma to the pretracheal muscles, which are separated vertically in the midline to expose the pre tracheal fascia. This fascia is incised transversely and is dissected off the trachea, creating a "tunnel" between the pretracheal fascia and trachea into the mediastinum. This "tunnel" is enlarged by finger dissection distally to the bifurcation of the
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Figure 1. Superior mediastinal lymph nodes generally accessible by cervical mediastinoscopy.
tracheobronchial angle anterior subcarinal
trachea and laterally along the sides of the trachea. The superior mediastinal lymph nodes lie "outside" the pre tracheal fascia, which must be digitally broken down in order to expose the nodes. Palpation in all regions is extremely important. This will allow the surgeon to identifY potentially involved sites of disease prior to inserting the mediastinoscope. The finger is withdrawn and the mediastinoscope is inserted. In every case we routinely identifY lymph nodes in both tracheobronchial angles, in the ipsilateral paratracheal region, in the subcarinal area (Fig. 2), and in the pretracheal (inferior to the innominate artery) space, removing lymph node samples for' histologic examination. The dissection of lymph nodes and exploration of the mediastinum are facilitated by using the open tip of an appropriate length metal suction catheter. The subcarinal space is invested by thick fascia anteriorly, which must be opened in order to reach the lymph nodes. The fascia is broken down by more forceful dissection with the open-tip suction catheter. This exploration and the subsequent biopsies must be performed gently. It is not necessary to completely remove each lymph node, but only to obtain adequate samples. In most instances, if mediastinoscopy is done properly, no complications ensue. Bleeding is usually minimal. The wound is closed primarily without drains.
Figure 2. A diagram to illustrate the mediastinoscope in place during biopsy of anterior subcarinal lymph nodes.
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Interpretation of Mediastinoscopy
At the time of mediastinoscopy, the surgeon can palpate and inspect the mediastinum. One can determine metastatic involvement of lymph nodes and, if involved, whether they can be removed completely at the time of surgical resection. Also, in some instances, direct extension of the tumor to the trachea, esophagus, vertebra posteriorly, and other mediastinal structures can be identified and assessed as to potential resectability. In our own experience, extensive involvement of the mediastinum by lymph nodes. or tumor indicates surgical incurability, by virtue of an inability to completely resect the disease. It is accepted that N3 (contralateral) nodes indicate inoperability. N2 (ipsilateral) lymph nodes macroscopically involved with or completely replaced by tumor that is also invading the mediastinal fat planes will ultimately result in an incomplete resection. Similarly, involved ipsilateral paratracheallymph nodes from left upper lobe tumors cannot be adequately resected by standard thoracotomy. In these cases, a "positive" mediastinoscopy would indicate inoperability. We have also found that virtually any involvement of the anterior subcarinal group of nodes indicates massive involvement in the rest of the subcarinal space. Rarely can this type of involvement be completely resected at thoracotomy. We have found that only 10 per cent of patients with "positive" mediastinoscopy will be considered to have resectable, potentially curable disease. Results of Mediastinoscopy
Mediastinoscopy has been shown to be a very safe procedure. In two recent reports of the results of mediastinoscopy in the assessment of lung cancer, 2259 mediastinoscopies were analyzed. 5. 10 There were no deaths attributable to this investigation. The total complication rate was 2.0 per cent; only 0.3 per cent of the complications were significant enough to require surgical treatment (thoracotomy or sternotomy). The significant lifethreatening complications were hemorrhage, tracheobronchial injury, and esophageal injury. More commonly, lesser complications, including pneumothorax, recurrent nerve injury and wound infection, occur (Table 1). Mediastinoscopy has a high positive predictive value. There should be no false-positive analyses, and the false-negative rate should be less than 10 per cent. In most instances of "false-negative" mediastinoscopy, the N2 disease identified at subsequent thoracotomy is in lymph node sites that are inaccessible by the mediastinoscope but accessible for complete en bloc resection: anterior mediastinal nodes, posterior subcarinal nodes, low main stem bronchial nodes, nodes along the inferior pulmonary vein and periesophageal regions, and subaortic nodes (Fig. 3). With the use of mediastinoscopy, the rate of thoracotomies leading to unresectability has been minimized to 5 per cent or less. Also, over 90 per cent of resections will be complete ones. No other staging modality utilized to identify unresectable carcinoma by virtue of mediastinal extension is as accurate or yields as many complete resections at the time of thoracotomy. Low-lying ipsilateral N2 nodes (low paratracheal and tracheobronchial
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EVALUATION OF THE MEDIASTINUM BY INVASIVE TECHNIQUES
Table 1. Complications of Mediastinoscopy in 2259 Patients* PATIENTS
No.
Death Life-threatening complications Hemorrhage Tracheal injury Esophageal injury Major complications Recurrent nerve palsy Pneumothorax Minor complications Wound infection, wound hematoma, etc. Total
%
o
o
6 2 2 2
0.3
21
0.9
7 14
18
45
0.8 2.0
*Data from two recent large series. 5. 10
angle) minimally involved with tumor may still be completely resected at the time of thoracotomy. These account for the 10 per cent of patients with positive mediastinoscopies who are offered curative resection. Drawbacks of Medinastinoscopy. Mediastinoscopy requires a general anaesthetic. In inexperienced hands, there can be significant complications, including mortality. However, in those centers where mediastinoscopy is performed on a routine basis, the complications of the procedure are minimal. Many will argue that if a preoperative CT scan indicates no enlargement of mediastinal lymph nodes, thoracotomy can be advised without invasive staging, especially because the latter procedure requires a separate general
Figure 3. Anterior and posterior mediastinal lymph nodes inaccessible by standard cervical mediastinoscopy. (From Pearson FG: An evaluation of mediastinoscopy in the management of presumably operable bronchial carcinoma. J Thorac Cardiovasc Surg 55:617625, 1968; with permission.)
anterior
~----mediastinal
posterior -----subcarinal
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Figure 4. Anterior mediastinotomy can be used as illustrated to explore the superior mediastinum and the area of the superior vena cava and pulmonary artery on the right side. (From Jolly PC, Hill LD, Lawless PA, et al: Parasternal mediastinotomy and mediastinoscopy. J Thorac Cardiovasc Surg 66:549-556, 1973; with permission.)
pulmonary artery and vein
anesthetic. Because there is inherent in noninvasive staging techniques a higher false-negative rate, we have adopted the policy of performing mediastinoscopy just prior to thoracotomy under the same general anesthetic in those patients who have no radiologic evidence of mediastinal disease. Advantages of Mediastinoscopy. If mediastinoscopy is not performed, radical mediastinal lymph node dissection, or at least multiple mediastinal lymph node biopsies, are required at the time of thoracotomy. If mediastinoscopy does not reveal metastatic disease, this type of staging procedure at thoracotomy is not necessary. The total time taken in the operating room for mediastinoscopy followed by thoracotomy should not be much greater than that taken for thoracotomy and mediastinal lymph node dissection. The former approach will avoid unnecessary thoracotomies in a number of cases. Mediastinoscopy is still considered to be the "gold standard" nodal staging procedure when assessing operability in patients with lung cancer.
ANTERIOR (PARASTERNAL) MEDIASTINOTOMY
Exploration of the anterior mediastinum is indicated in left upper lobe tumors to exclude extensive nodal involvement in the subaortic and lateral aortic areas. It can also be used in right-sided tumors to assess involvement of the proximal pulmonary artery and superior vena cava (Fig. 4). In left upper lobe tumors, we have always combined this approach with standard cervical mediastinoscopy. When N2 disease is present in left upper lobe tumors, in over half the cases, disease has spread to the superior mediastinum, an area that cannot be assessed using a Chamberlain approach
EVALUATION OF THE MEDIASTINUM BY INVASIVE TECHNIQUES
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Figure 5. Extrapleural exposure by anterior mediastinotomy to demonstrate the subaortic space and recurrent nerve. (From Jolly PC, Hill LD, Lawless PA, et al: Parasternal mediastinotomy and mediastinoscopy. J Thorac Cardiovasc Surg 66:549-556, 1973; with permission.)
artery and vein
alone. As well, bimanual palpation of the anterior mediastinum using both cervical and anterior incisions simultaneously can help to assess the fixation of tumor in the subaortic region. Technique The original technique as described by McNeil and Chamberlain 12 includes a vertical parasternal incision over the second and third costal cartilages and resection of these cartilages. Many modifications have been described. 9, 17 We prefer to use a short transverse incision over the second costal cartilage, which is excised. Others advocate an intercostal exploration without any cartilage excision. An extrapleural or intrapleural approach may be used. The intrapleural approach will allow exploration of the primary tumor and assessment of the pleural spread. However, the lymph nodes requiring biopsy lie extrapleurally, between the parietal pleura and mediastinal fascia. For accurate biopsy of these nodes, the extrapleural approach is required (Fig. 5). Care must be taken not to damage the internal mammary vessels, which are located as the parietal pleura reflects off the mediastinum onto the anterior chest wall. A finger is inserted into the anterior mediastinal area, and if a cervical mediastinoscopy has also been used, the index finger of the other hand is inserted into the superior mediastinum. This bimanual palpation of the subaortic space and arch area can be helpful in determining tumor fixation (Fig. 6). The mediastinoscope is then inserted to identify and sample lymph nodes in the subaortic and lateral aortic regions for biopsy. Palpation along the internal mammary artery will identify any spread to its associated lymph nodes.
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Figure 6. Bimanual palpation through an anterior mediastinotomy incision combined with cervical mediastinoscopy allows determination of fixation of the subaortic space.
Closure of the wound does not require drainage if an extrapleural approach has been performed. If the pleura has been entered, simple "bagging" of the lung by the anesthetist while the wound is being closed will avoid pneumothorax as well as the necessity of an intercostal tube. Interpretation of Results
Microscopic involvement of subaortic nodes does not necessarily preclude complete resection of a tumor. 14 Such an N2 tumor is still operable and curable. Invasion and fixation of the mediastinum by the tumor or lymph nodes, however, will almost certainly lead to an incomplete resection and little chance of cure. The value of anterior mediastinotomy lies in its ability to assess invasion and fixation of the mediastinum by tumor or lymph nodes.
EXTENDED CERVICAL MEDIASTINOSCOPY We have employed an extension of cervical mediastinoscopy rather than anterior mediastinotomy to assess spread of left upper lobe tumors. 12 Once cervical mediastinoscopy is completed, the space superolateral to the aorta, between the innominate artery and left common carotid artery, is opened by finger dissection. The mediastinoscope can then be inserted through this space after the fascia enveloping it has been broken down digitally. The mediastinoscope passes over the aortic arch and into the subaortic region. Anterior mediastinal and subaortic lymph nodes can be identified and sampled for biopsy with this simple technique (Fig. 7). The ability to assess fixation of the mediastinum using this extended mediastinoscopy technique is not as accurate as using the combined mediastinoscopy-anterior mediastinotomy approach. On occasion, if this type of fixation
EVALUATION OF THE MEDIASTINUM BY INVASIVE TECHNIQUES
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Figure 7. In extended cervical mediastinoscopy, the mediastinoscope can be used to inspect the anterior mediastinal compartment including the subaortic space.
is questioned, an anterior mediastinotomy is also performed for complete assessment. However, this has been required only on rare occasions. This "extended" cervical mediastinoscopy eliminates the need for a second incision and allows for rapid assessment of both the superior and anterior mediastinal areas in left upper lobe tumors. In over half of the patients found to have N2 disease, cervical mediastinoscopy alone has identified the involved nodes. Further exploration then becomes unnecessary, because superior mediastinal lymph nodes associated with a left upper lobe tumor necessarily make a complete resection unattainable and the tumor inoperable. SCALENE NODE BIOPSY
Although technically not an exploration of the mediastinum, scalene node biopsy can still be valuable in assessing patients with N2 disease. In
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those cases in which operable N2 disease has been identified at mediastinoscopy, we routinely perform blind scalene node biopsy on the ipsilateral side. We have found, much to our chagrin, that on occasion, although only low "resectable" mediastinal nodes have been identified at mediastinoscopy to be involved with tumor, blind scalene node biopsy has identified "skip" areas of metastatic tumor in this location. The scalene node biopsy can be done by extending the cervical mediastinoscopy incision laterally one or two centimeters and utilizing the technique as described by Daniels. 6 We have made it a policy to perform this biopsy prior to resection in patients preoperatively identified as having N2 disease. Rarely is scalene node biopsy used to prove metastatic disease in this area if nodes are palpable. A much simpler approach is percutaneous fineneedle aspiration biopsy of the enlarged lymph node for cytologic examination. POSTERIOR MEDIASTINOTOMY Exploration of the posterior mediastinum through a small incision, resecting the posterior aspect of a rib, will identify disease invading the posterior mediastinum, usually by virtue of direct tumor invasion. We rarely require this approach because of the utilization of CT scanning and percutaneous fine-needle aspiration biopsy in this situation. On occasion, however, posterior mediastinotomy can be used to avoid an unnecessary thoracotomy. TRANS BRONCHIAL NEEDLE ASPIRATION BIOPSY Wang and associates 18 have described staging of the mediastinum with a flexible bronchoscope and trans bronchial needle aspiration biopsy of subcarinal nodes and ipsilateral paratracheal nodes. This technique is best performed after CT examination of the mediastinum indicates nodal enlargement. Thus, a CT-directed biopsy can be done. There is, however, a high false-negative rate and a small but significant false-positive rate (usually due to needle aspiration of the primary tumor rather than lymph nodes). Also, this technique cannot identify multiple levels of lymph node disease or technical resectability of minimally involved lymph nodes. Nevertheless, transbronchial needle aspiration biopsy is of value when clinically obvious, inoperable mediastinal lymph node disease is present and requires only cytologic or histologic confirmation.
CONCLUSIONS The value of invasive staging of the mediastinum is its greater accuracy in assessing the operability of lung cancer compared with noninvasive techniques. In expert hands, invasive mediastinal exploration has very low
EVALUATION OF THE MEDIASTINUM BY INVASIVE TECHNIQUES
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morbidity and mortality. For all of these reasons, we continue to use mediastinoscopy as a routine part of the evaluation of the mediastinum prior to advising thoracotomy for resection in the management of lung cancer.
REFERENCES 1. Allison PR: Intrapericardial approach to the lung route in achievement of bronchial carcinoma by dissection pneumonectomy. J Thorax Surg 15:99, 1946 2. Brion JP, Depau WL, Kuhn G, et al: Role of computed tomography and mediastinoscopy in preoperative staging of lung cancer. J Comput Assist Tomogr 3:480--484, 1985 3. Brock RC: Bronchial carcinoma. Br Med J 2:737, 1948 4. Carlens E: Mediastinoscopy: A method for inspection and tissue biopsy in the superior mediastinum. Chest 36:343, 1949 5. Coughlin M, Deslaurier J, Beaulieu M, et al: Role of mediastinoscopy and pre-treatment staging in patients with primary lung cancer. Ann Thorac Surg 40:556-559, 1985 6. Daniels AS: A method of biopsy useful in diagnosing intrathoracic diseases. Chest 16:360, 1949 7. Ginsberg RJ, Rice TW, Goldberg M, et al: Extended cervical mediastinoscopy-the best procedure for staging left upper lobe tumours. J Thorac Cardiovasc Surg (in press) 8. Harkens DE, Black H, Clauss R, et al: A single cervical-mediastinal exploration for tissue diagnosis of intrathoracic disease. N Engl J Med 251:1041, 1954 9. Jolly PC, Hill LE, Lawlass PA, et al: Parasternal mediastinotomy and mediastinoscopy. J Thorac Cardiovasc Surg 66:549-556, 1973 10. Luke WP, Pearson FG, Todd TRJ, et al: Prospective evaluation of mediastinoscopy for assessment of carcinoma of the lung. J Thorac Cardiovasc Surg 91:553-556, 1986 11. Martini N, Flehinger BJ, Zaman MB, Beattie EJ Jr: Results of resection in non-oat cell carcinoma of the lung with mediastinal lymph node metastases. Ann Surg 198:386-397, 1983 12. McNeil TM, Cha,nberlain JM: Diagnostic anterior mediastinotomy. Ann Thorac Surg 2:532,1966 13. Mountain CF: A new international staging system for lung cancer. Chest 89:225S-233S, 1986 14. Patterson GA, Piazza D, Pearson FG, et al: Significance of metastatic disease in subaortic lymph nodes. Ann Thorac Surg 43:155-159, 1987 15. Pearson FG: Mediastinoscopy: A method of biopsy in the superior mediastinum. J Thorac Cardiovasc Surg 49:11, 1965 16. Pearson FG, Delarue NC, lives R, et al: Significance of positive superior mediastinal nodes identified at mediastinoscopy in patients with resectable cancer of the lung. J Thorac Cardiovasc Surg 83:1-11, 1982 17. Stemmer EA, Calvin JW, Steedman RA, et al: Parasternal mediastinal exploration to evaluate resectability of thoracic neoplasms. Ann Thorac Surg 12:375, 1971 18. Wang KP, Brower R, Haponik EF, Siegelman S: Flexible transbronchial needle aspiration for staging bronchogenic carcinoma. Chest 84:571-576, 1983 Division of Thoracic Surgery Mount Sinai Hospital Suite 451 600 University Avenue Toronto, Ontario M5G 1X5 Canada
0039-6109/87 $0.00
+ .20
Evaluation of the Mediastinum by Invasive Techniques
Robert]. Ginsberg, M.D., F.R.C.S.(C)*
Once lung cancer has spread to mediastinal lymph nodes, the ultimate prognosis, despite complete surgical removal of the primary tumor and involved lymph nodes, is markedly worsened. This poor prognosis was recognized by many early thoracic surgeons, 1, 3 and attempts were made to identifY tumor spread to the lymph nodes of the mediastinum preoperatively, in order to avoid unnecessary thoracotomies for inoperable situations, The classic report by Daniels 6 indicated that scalene node biopsy, even in nonpalpable disease, would identifY a group of patients whose disease had spread even beyond the mediastinum to the lower reaches of the neck. Harkens and associates 8 were the first to introduce invasive staging of the mediastinum, describing a "cervical mediastinal exploration" using a Jackson laryngoscope through a cervical incision. This enabled the surgeon to palpate and directly inspect the superior mediastinum and afforded the opportunity to sample lymph nodes in that location for biopsy. Cervical mediastinoscopy as performed today was developed by Carlens 4 and popularized in North America by Pearson. 15 Exploration of the anterior mediastinum, especially in staging of left upper lobe tumors, was first advocated by McNeil and Chamberlain. 12 We have recently described the results of exploring this area of the mediastinum utilizing a standard cervical mediastinoscopy approach. 7 Transbronchoscopic needle aspiration of subcarinal lymph nodes has been used for many years in attempting to identifY involvement in this area. More recently, Wang and associates 18 have further refined this technique using a flexible bronchoscope and performing fine-needle aspiration biopsies of the subcarinal and paratracheal regions. It is claimed that N2 and N3 disease can be identified by this technique, thereby avoiding mediastinoscopy. Occasionally, exploration of the posterior mediastinum is utilized to *Surgeon-in-Chief and Head, Division of Thoracic Surgery, Mount Sinai Hospital; Professor, University of Toronto; and Consultant and Thoracic Surgeon, Princess Margaret Hospital and the Ontario Cancer Institute, Toronto, Ontario, Canada
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identify spread of lung cancer in this region, a discovery that would avoid a subsequent major thoracotomy.
INVASIVE VERSUS NONINVASIVE STAGING
Should all patients, prior to thoracotomy, undergo surgical exploration of the mediastinum to exclude the presence of inoperable N2 and N3 disease? Many argue that with the newer noninvasive (computed tomography, magnetic resonance imaging) and minimally invasive techniques (transbronchial needle aspiration biopsy), mediastinoscopy can be avoided unless results of these investigations suggest significant involvement of the mediastinum. 2,18 Mediastinoscopy, in this situation, would be used to confirm inoperability in selected cases. Others, myself included, believe that mediastinoscopy is such a safe and informative staging procedure that it should be used routinely in virtually every patient prior to thoracotomy. It avoids the 10 per cent false-negative rate inherent in all noninvasive techniques. This controversy persists and has been the subject of many articles and symposia. The results of surgery when N2 or N3 disease is resected are well known. 11, 16 Incompletely resected mediastinal nodal disease rarely, if ever, results in long-term cure, and the palliative value of such resections is questionable. Mediastinoscopy and anterior mediastinotomy will identify those patients whose tumors cannot be completely resected, by virtue of advanced N2, N3, or T4 disease. 13 It is these patients with Stage III disease who will benefit from mediastinal exploration, avoiding an unnecessary thoracotomy. Most surgeons would agree that if this type of advanced disease is identified at mediastinoscopy, no resectional surgery should be performed.
CERVICAL MEDIASTINOSCOPY
Exploration of the superior mediastinum by cervical mediastinoscopy enables the surgeon to biopsy the lymph nodes: in the anterior aspect of the subcarinal space, around the proximal main stem bronchi and lower trachea (tracheobronchial angle nodes), and in the pretracheal and paratracheal regions (Fig. 1). Complete lymph node staging of the superior mediastinum is thus possible. Technique
For adequate exposure, the patient is supine with the neck extended and the shoulders elevated by a bolster underneath. A small (3 to 4 cm) transverse incision is made 1 cm above the suprasternal notch and is carried down through platysma to the pretracheal muscles, which are separated vertically in the midline to expose the pre tracheal fascia. This fascia is incised transversely and is dissected off the trachea, creating a "tunnel" between the pretracheal fascia and trachea into the mediastinum. This "tunnel" is enlarged by finger dissection distally to the bifurcation of the
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Figure 1. Superior mediastinal lymph nodes generally accessible by cervical mediastinoscopy.
tracheobronchial angle anterior subcarinal
trachea and laterally along the sides of the trachea. The superior mediastinal lymph nodes lie "outside" the pre tracheal fascia, which must be digitally broken down in order to expose the nodes. Palpation in all regions is extremely important. This will allow the surgeon to identifY potentially involved sites of disease prior to inserting the mediastinoscope. The finger is withdrawn and the mediastinoscope is inserted. In every case we routinely identifY lymph nodes in both tracheobronchial angles, in the ipsilateral paratracheal region, in the subcarinal area (Fig. 2), and in the pretracheal (inferior to the innominate artery) space, removing lymph node samples for' histologic examination. The dissection of lymph nodes and exploration of the mediastinum are facilitated by using the open tip of an appropriate length metal suction catheter. The subcarinal space is invested by thick fascia anteriorly, which must be opened in order to reach the lymph nodes. The fascia is broken down by more forceful dissection with the open-tip suction catheter. This exploration and the subsequent biopsies must be performed gently. It is not necessary to completely remove each lymph node, but only to obtain adequate samples. In most instances, if mediastinoscopy is done properly, no complications ensue. Bleeding is usually minimal. The wound is closed primarily without drains.
Figure 2. A diagram to illustrate the mediastinoscope in place during biopsy of anterior subcarinal lymph nodes.
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Interpretation of Mediastinoscopy
At the time of mediastinoscopy, the surgeon can palpate and inspect the mediastinum. One can determine metastatic involvement of lymph nodes and, if involved, whether they can be removed completely at the time of surgical resection. Also, in some instances, direct extension of the tumor to the trachea, esophagus, vertebra posteriorly, and other mediastinal structures can be identified and assessed as to potential resectability. In our own experience, extensive involvement of the mediastinum by lymph nodes. or tumor indicates surgical incurability, by virtue of an inability to completely resect the disease. It is accepted that N3 (contralateral) nodes indicate inoperability. N2 (ipsilateral) lymph nodes macroscopically involved with or completely replaced by tumor that is also invading the mediastinal fat planes will ultimately result in an incomplete resection. Similarly, involved ipsilateral paratracheallymph nodes from left upper lobe tumors cannot be adequately resected by standard thoracotomy. In these cases, a "positive" mediastinoscopy would indicate inoperability. We have also found that virtually any involvement of the anterior subcarinal group of nodes indicates massive involvement in the rest of the subcarinal space. Rarely can this type of involvement be completely resected at thoracotomy. We have found that only 10 per cent of patients with "positive" mediastinoscopy will be considered to have resectable, potentially curable disease. Results of Mediastinoscopy
Mediastinoscopy has been shown to be a very safe procedure. In two recent reports of the results of mediastinoscopy in the assessment of lung cancer, 2259 mediastinoscopies were analyzed. 5. 10 There were no deaths attributable to this investigation. The total complication rate was 2.0 per cent; only 0.3 per cent of the complications were significant enough to require surgical treatment (thoracotomy or sternotomy). The significant lifethreatening complications were hemorrhage, tracheobronchial injury, and esophageal injury. More commonly, lesser complications, including pneumothorax, recurrent nerve injury and wound infection, occur (Table 1). Mediastinoscopy has a high positive predictive value. There should be no false-positive analyses, and the false-negative rate should be less than 10 per cent. In most instances of "false-negative" mediastinoscopy, the N2 disease identified at subsequent thoracotomy is in lymph node sites that are inaccessible by the mediastinoscope but accessible for complete en bloc resection: anterior mediastinal nodes, posterior subcarinal nodes, low main stem bronchial nodes, nodes along the inferior pulmonary vein and periesophageal regions, and subaortic nodes (Fig. 3). With the use of mediastinoscopy, the rate of thoracotomies leading to unresectability has been minimized to 5 per cent or less. Also, over 90 per cent of resections will be complete ones. No other staging modality utilized to identify unresectable carcinoma by virtue of mediastinal extension is as accurate or yields as many complete resections at the time of thoracotomy. Low-lying ipsilateral N2 nodes (low paratracheal and tracheobronchial
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Table 1. Complications of Mediastinoscopy in 2259 Patients* PATIENTS
No.
Death Life-threatening complications Hemorrhage Tracheal injury Esophageal injury Major complications Recurrent nerve palsy Pneumothorax Minor complications Wound infection, wound hematoma, etc. Total
%
o
o
6 2 2 2
0.3
21
0.9
7 14
18
45
0.8 2.0
*Data from two recent large series. 5. 10
angle) minimally involved with tumor may still be completely resected at the time of thoracotomy. These account for the 10 per cent of patients with positive mediastinoscopies who are offered curative resection. Drawbacks of Medinastinoscopy. Mediastinoscopy requires a general anaesthetic. In inexperienced hands, there can be significant complications, including mortality. However, in those centers where mediastinoscopy is performed on a routine basis, the complications of the procedure are minimal. Many will argue that if a preoperative CT scan indicates no enlargement of mediastinal lymph nodes, thoracotomy can be advised without invasive staging, especially because the latter procedure requires a separate general
Figure 3. Anterior and posterior mediastinal lymph nodes inaccessible by standard cervical mediastinoscopy. (From Pearson FG: An evaluation of mediastinoscopy in the management of presumably operable bronchial carcinoma. J Thorac Cardiovasc Surg 55:617625, 1968; with permission.)
anterior
~----mediastinal
posterior -----subcarinal
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Figure 4. Anterior mediastinotomy can be used as illustrated to explore the superior mediastinum and the area of the superior vena cava and pulmonary artery on the right side. (From Jolly PC, Hill LD, Lawless PA, et al: Parasternal mediastinotomy and mediastinoscopy. J Thorac Cardiovasc Surg 66:549-556, 1973; with permission.)
pulmonary artery and vein
anesthetic. Because there is inherent in noninvasive staging techniques a higher false-negative rate, we have adopted the policy of performing mediastinoscopy just prior to thoracotomy under the same general anesthetic in those patients who have no radiologic evidence of mediastinal disease. Advantages of Mediastinoscopy. If mediastinoscopy is not performed, radical mediastinal lymph node dissection, or at least multiple mediastinal lymph node biopsies, are required at the time of thoracotomy. If mediastinoscopy does not reveal metastatic disease, this type of staging procedure at thoracotomy is not necessary. The total time taken in the operating room for mediastinoscopy followed by thoracotomy should not be much greater than that taken for thoracotomy and mediastinal lymph node dissection. The former approach will avoid unnecessary thoracotomies in a number of cases. Mediastinoscopy is still considered to be the "gold standard" nodal staging procedure when assessing operability in patients with lung cancer.
ANTERIOR (PARASTERNAL) MEDIASTINOTOMY
Exploration of the anterior mediastinum is indicated in left upper lobe tumors to exclude extensive nodal involvement in the subaortic and lateral aortic areas. It can also be used in right-sided tumors to assess involvement of the proximal pulmonary artery and superior vena cava (Fig. 4). In left upper lobe tumors, we have always combined this approach with standard cervical mediastinoscopy. When N2 disease is present in left upper lobe tumors, in over half the cases, disease has spread to the superior mediastinum, an area that cannot be assessed using a Chamberlain approach
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Figure 5. Extrapleural exposure by anterior mediastinotomy to demonstrate the subaortic space and recurrent nerve. (From Jolly PC, Hill LD, Lawless PA, et al: Parasternal mediastinotomy and mediastinoscopy. J Thorac Cardiovasc Surg 66:549-556, 1973; with permission.)
artery and vein
alone. As well, bimanual palpation of the anterior mediastinum using both cervical and anterior incisions simultaneously can help to assess the fixation of tumor in the subaortic region. Technique The original technique as described by McNeil and Chamberlain 12 includes a vertical parasternal incision over the second and third costal cartilages and resection of these cartilages. Many modifications have been described. 9, 17 We prefer to use a short transverse incision over the second costal cartilage, which is excised. Others advocate an intercostal exploration without any cartilage excision. An extrapleural or intrapleural approach may be used. The intrapleural approach will allow exploration of the primary tumor and assessment of the pleural spread. However, the lymph nodes requiring biopsy lie extrapleurally, between the parietal pleura and mediastinal fascia. For accurate biopsy of these nodes, the extrapleural approach is required (Fig. 5). Care must be taken not to damage the internal mammary vessels, which are located as the parietal pleura reflects off the mediastinum onto the anterior chest wall. A finger is inserted into the anterior mediastinal area, and if a cervical mediastinoscopy has also been used, the index finger of the other hand is inserted into the superior mediastinum. This bimanual palpation of the subaortic space and arch area can be helpful in determining tumor fixation (Fig. 6). The mediastinoscope is then inserted to identify and sample lymph nodes in the subaortic and lateral aortic regions for biopsy. Palpation along the internal mammary artery will identify any spread to its associated lymph nodes.
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Figure 6. Bimanual palpation through an anterior mediastinotomy incision combined with cervical mediastinoscopy allows determination of fixation of the subaortic space.
Closure of the wound does not require drainage if an extrapleural approach has been performed. If the pleura has been entered, simple "bagging" of the lung by the anesthetist while the wound is being closed will avoid pneumothorax as well as the necessity of an intercostal tube. Interpretation of Results
Microscopic involvement of subaortic nodes does not necessarily preclude complete resection of a tumor. 14 Such an N2 tumor is still operable and curable. Invasion and fixation of the mediastinum by the tumor or lymph nodes, however, will almost certainly lead to an incomplete resection and little chance of cure. The value of anterior mediastinotomy lies in its ability to assess invasion and fixation of the mediastinum by tumor or lymph nodes.
EXTENDED CERVICAL MEDIASTINOSCOPY We have employed an extension of cervical mediastinoscopy rather than anterior mediastinotomy to assess spread of left upper lobe tumors. 12 Once cervical mediastinoscopy is completed, the space superolateral to the aorta, between the innominate artery and left common carotid artery, is opened by finger dissection. The mediastinoscope can then be inserted through this space after the fascia enveloping it has been broken down digitally. The mediastinoscope passes over the aortic arch and into the subaortic region. Anterior mediastinal and subaortic lymph nodes can be identified and sampled for biopsy with this simple technique (Fig. 7). The ability to assess fixation of the mediastinum using this extended mediastinoscopy technique is not as accurate as using the combined mediastinoscopy-anterior mediastinotomy approach. On occasion, if this type of fixation
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Figure 7. In extended cervical mediastinoscopy, the mediastinoscope can be used to inspect the anterior mediastinal compartment including the subaortic space.
is questioned, an anterior mediastinotomy is also performed for complete assessment. However, this has been required only on rare occasions. This "extended" cervical mediastinoscopy eliminates the need for a second incision and allows for rapid assessment of both the superior and anterior mediastinal areas in left upper lobe tumors. In over half of the patients found to have N2 disease, cervical mediastinoscopy alone has identified the involved nodes. Further exploration then becomes unnecessary, because superior mediastinal lymph nodes associated with a left upper lobe tumor necessarily make a complete resection unattainable and the tumor inoperable. SCALENE NODE BIOPSY
Although technically not an exploration of the mediastinum, scalene node biopsy can still be valuable in assessing patients with N2 disease. In
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those cases in which operable N2 disease has been identified at mediastinoscopy, we routinely perform blind scalene node biopsy on the ipsilateral side. We have found, much to our chagrin, that on occasion, although only low "resectable" mediastinal nodes have been identified at mediastinoscopy to be involved with tumor, blind scalene node biopsy has identified "skip" areas of metastatic tumor in this location. The scalene node biopsy can be done by extending the cervical mediastinoscopy incision laterally one or two centimeters and utilizing the technique as described by Daniels. 6 We have made it a policy to perform this biopsy prior to resection in patients preoperatively identified as having N2 disease. Rarely is scalene node biopsy used to prove metastatic disease in this area if nodes are palpable. A much simpler approach is percutaneous fineneedle aspiration biopsy of the enlarged lymph node for cytologic examination. POSTERIOR MEDIASTINOTOMY Exploration of the posterior mediastinum through a small incision, resecting the posterior aspect of a rib, will identify disease invading the posterior mediastinum, usually by virtue of direct tumor invasion. We rarely require this approach because of the utilization of CT scanning and percutaneous fine-needle aspiration biopsy in this situation. On occasion, however, posterior mediastinotomy can be used to avoid an unnecessary thoracotomy. TRANS BRONCHIAL NEEDLE ASPIRATION BIOPSY Wang and associates 18 have described staging of the mediastinum with a flexible bronchoscope and trans bronchial needle aspiration biopsy of subcarinal nodes and ipsilateral paratracheal nodes. This technique is best performed after CT examination of the mediastinum indicates nodal enlargement. Thus, a CT-directed biopsy can be done. There is, however, a high false-negative rate and a small but significant false-positive rate (usually due to needle aspiration of the primary tumor rather than lymph nodes). Also, this technique cannot identify multiple levels of lymph node disease or technical resectability of minimally involved lymph nodes. Nevertheless, transbronchial needle aspiration biopsy is of value when clinically obvious, inoperable mediastinal lymph node disease is present and requires only cytologic or histologic confirmation.
CONCLUSIONS The value of invasive staging of the mediastinum is its greater accuracy in assessing the operability of lung cancer compared with noninvasive techniques. In expert hands, invasive mediastinal exploration has very low
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morbidity and mortality. For all of these reasons, we continue to use mediastinoscopy as a routine part of the evaluation of the mediastinum prior to advising thoracotomy for resection in the management of lung cancer.
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