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Eur J Cardiothorac Surg 2004;25:497-501
© 2004 Elsevier Science NL
a Department of Thoracic surgery, Glenfield Hospital, Groby Road, Leicester LE3 9QP, UK
b Department of Pathology, Glenfield Hospital, Groby Road, Leicester LE3 9QP, UK
c Department of Oncology, Glenfield Hospital, Groby Road, Leicester LE3 9QP, UK
Received 6 September 2003; received in revised form 25 November 2003; accepted 1 December 2003.
* Corresponding author. Tel.: +44-116-256-3959; fax: +44-116-236-7768
e-mail: debra.grew{at}uhl-tr.nhs.uk
| Abstract |
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Key Words: Malignant pleural mesothelioma Staging Thoracic surgery Lymph nodes
| 1. Introduction |
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In the non-invasive assessment of mediastinal nodes in non-small cell lung cancer (NSCLC), nodes containing metastases are believed to be larger than those that do not and nodes with a short axis of 10 mm or long axis of 15 mm are believed to be positive [6]. We evaluated the size of lymph nodes in lymphadenectomy specimens from patients who underwent radical excision for MPM to assess whether nodal size is a predictor of metastatic involvement in MPM as it is considered to be in NSCLC.
| 2. Methods |
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All patients had undergone CT scan of the thorax and upper abdomen before referral and these were assessed to determine resectability and mediastinal lymph node status. No patient had any clinical evidence of extra thoracic disease. Patients then proceeded to contrast enhanced magnetic resonance imaging of the thorax and upper abdomen as already described [8]. Resectability was defined by tumour confined to one hemithorax, with the absence of mediastinal organ or full-thickness pericardial/myocardial involvement, absence of diffuse or multifocal chest wall disease, transdiaphragmatic extension or spread directly into the spine, hence excluding stage T4 disease. Contrast enhancement of sites of previous entry to the chest were not, in themselves, seen as any contraindication to radical surgery, as these were widely excised. The single patient with enlarged mediastinal lymph nodes on CT scan underwent preoperative cervical mediastinoscopy which did not demonstrate malignancy. During the early part of this study fluorodeoxyglucose positron emission tomography (PET) scan was not available in Leicester and was not used in any of the patients in the latter part of the study as they had no symptoms of metastatic disease or evidence of upper abdominal spread on cross-sectional imaging.
Over a 48-month period 55 patients underwent radical excision of MPM in a single thoracic surgical practice. They comprised 50 men and 5 women, median age 58 years (range 4170 years). They underwent four radical pleurectomies and 51 extra pleural pneumonectomies. Thirty-one patients underwent right-sided operations and 24 left. Fifty patients were found to have epithelioid MPM, four biphasic MPM and one sarcomatoid MPM. In all patients systematic mediastinal lymph node dissection was performed to allow accurate surgical staging of the disease. Nodes were sampled from station 7 and at least two other extra pleural stations in each patient. All macroscopically abnormal lymph nodes were cleared. All patients were prospectively followed for signs of recurrence and death. All patients were referred to an oncologist for consideration of adjuvant treatment. Postoperative survival was compared between those patients with and without extra pleural lymph node metastases.
2.2. Lymph node analysis
Postoperative pathological analysis had recorded the long axis diameter of 99n of the 436 lymph nodes excised at operation. These nodes had been fixed in 5% formaldehyde and then measured. The lymph nodes were then embedded in wax and sections performed through each lymph node. These were stained with haematoxylin and eosin before examination by light microscopy to determine the presence of metastatic tumour.
2.3. Statistical analysis
The long axis diameter of lymph nodes with or without metastatic involvement was compared by Student's t-test. Postoperative survival of the patients with or without extra pleural lymph node metastases was compared using KaplanMeier log rank analysis.
| 3. Results |
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The overall median survival of the patients was 12.5 postoperative months (95% confidence intervals (CI) 5.419.6 months). The median postoperative survival of those patients with extra pleural lymph node metastases was 4.4 months (95% CI 3.35.4 months) significantly less than those without extra pleural lymph node metastases which was 16.3 months (95% CI 11.621.0 months) P=0.012 on KaplanMeier log rank analysis, see Fig 1 .
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Thirty-five patients had extra pleural lymph nodes whose long axis was greater than 15 mm; only eight of them contained metastases on histological examination. Twenty patients had no lymph nodes with a long axis diameter less than 15 mm and of these nine had metastases to extra pleural nodes. Nodes were sampled from most of the Naruke extra pleural lymph node stations [9], see Fig. 2 .
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| 4. Discussion |
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We have shown in our study that extra pleural lymph node metastases are related to a significantly poorer prognosis after radical resection of MPM. This confirms the published findings of other groups [4,5]. In fact the patients with extra pleural lymph node disease who underwent radical resection have a similar survival to the series of patients diagnosed with MPM in Leicester between 1988 and 1998; only eight of 138 underwent radical surgery [2].
We have also shown that the long axis diameter of lymph nodes containing metastatic tumour is not significantly different from those free of tumour in patients with MPM. These findings are similar to those of Prenzel et al. who showed that lymph node size was not a reliable parameter for evaluation of metastatic involvement in NSCLC [12]. The long axis diameter of the mediastinal nodes free from metastatic involvement was significantly smaller than those involved (7.07 mm compared to 11.3 mm, P=0.005). Of all lymph nodes less than 10 mm in diameter 8.4% were involved with tumour and only 30% of those larger than 10 mm were involved.
Wathen et al. in their series investigating the role of CT in the preoperative assessment of NSCLC showed that lymph node size did not correlate with metastatic involvement and hence recommended that all mediastinal lymph nodes visualised on CT should be biopsied prior to pulmonary resection [13]. The Canadian Lung Oncology Group showed in their randomised control trial that reserving mediastinoscopy for patients with mediastinal lymph nodes greater than 10 mm on CT scan was as good as routine cervical mediastinoscopy [14].
As the size of lymph nodes is not significantly different if they are involved by metastatic MPM it must be the case that preoperative imaging using size criteria will be unreliable in staging extra pleural lymph node metastases in patients with MPM. Studies using CT to stage MPM nodal status have reported poor results with accuracy rates of 67% [11] and 75% [15].
The optimal role of cervical mediastinoscopy in the preoperative assessment of patients for radical resection of MPM remains to be determined. A recent study has shown cervical mediastinoscopy accurately staged extra pleural lymph node metastases in 93% of patients who went on to have radical resection of MPM [11]. In 14 of the 17 patients with extra pleural lymph node metastases in our series the positive nodes were accessible by cervical mediastinoscopy i.e. stations 2R, 4R, 7 and 2L. Schouwink et al. report that lymph nodes not accessible to mediastinoscopy were found to be positive in six of 25 patients who underwent thoracotomy and who previously had negative mediastinoscopy in their study [11]. Out of the 82 mediastinal nodal positive cases reported by Rusch et al. 41 had metastases to stations accessible to mediastinoscopy [5]. Of 32 patients who were surgically staged by Maggi et al. nine had extra pleural lymph node involvement, four of whom accessible by cervical mediastinoscopy [10]. Sugarbaker et al. reported 40 patients with extra pleural lymph node metastases in a series of 176 patients. In 11 of the positive patients the metastases were to peridiaphragmatic nodes [3].
There has been recent interest in PET to stage MPM and a number of series have been published. In their series of 18 patients who underwent PET scan Schneider et al. reported that four patients had extra pleural lymph nodes identified by PET and proven on surgical biopsy. The negative PET scan of the mediastinal nodes was confirmed by surgical biopsy in 12 of the remaining 14 patients [16]. Bernard et al.'s series of 28 patients with suspected MPM showed PET scan positive mediastinal nodes in 12 patients; CT scan showed normal size nodes in nine patients. Biopsies were taken in six cases confirming metastases in five and granulomatous lymphadenitis in one. Of the 12 patients with a negative PET scan of their mediastinal nodes four had biopsies, three were negative and one positive for metastatic involvement [17]. Flores et al. showed that of 31 surgical staged patients, who underwent preoperative PET scan, nine had mediastinal nodal involvement but PET scan correctly identified only one of these [18].
We conclude that extra pleural lymph node metastases are a contraindication to radical resection of MPM. Imaging must be an unreliable method for assessing metastases from MPM to the extra pleural lymph nodes as the size of involved and uninvolved nodes are not significantly different and although PET scan has not rigorously tested it has been shown to assess the mediastinum inaccurately [18]. Cervical mediastinoscopy should be performed to accurately stage the patient's disease before offering radical tumour excision.
| Footnotes |
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| Appendix A. Conference discussion |
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Dr Pilling: Well, our findings agree with Sugarbaker's findings that extra pleural lymph node metastases do affect survival after operation, and therefore we would view them as a contraindication to proceeding to radical surgery. The issue in this presentation is the fact that you cannot stage them accurately preoperatively with imaging because the size of the lymph nodes are not affected by whether they are involved in the metastases or not.
Dr H. Hansen (Copenhagen, Denmark): Does your study not show the necessity of a PET/CT scan to image your lymph nodes?
Dr Pilling: We don't use PET on our patients for mesothelioma at the present time in Leicester, but there has been a recent paper by Valerie Rusch and colleagues who looked at 31 patients with surgically-proven nodal disease. Nine had N2 disease, but only one was correctly identified on PET scan preoperatively. And I think certainly PET scan on its own is inaccurate in staging mediastinal involvement. Whether CT/PET would be better, I don't know. I don't know of any data on that.
Dr S. Halezeroglu (Istanbul, Turkey): I'm very surprised to see that if one patient has N2 disease, this patient will die within 4 months of the operation. This is very surprising to me. And I know that no patient will die of N2 disease itself, because if one patient has N2 disease, this means that this patient has another distant metastasis and this will cause the death of this patient, and if you consider that these patients will be dying of distant metastasis but not the N2 disease itself, do you consider that these patients had distant metastasis during the operation?
Dr Pilling: No, I think we have made a reasonable search for distant metastases, including history, clinical examination and CT and MRI scan of the thorax and the upper abdomen. I'm not saying that they all died by 4 months after the operation. I'm saying their median survival is 4 months after the operation. So there are some that survive longer, but N2 disease does statistically predict a worse outcome.
Dr E. Ruffini (Chieri, Italy): I'm speaking on behalf of Professor Maggi.
I see in your series that half of your patients had metastases on the subcarinal nodes. How reliable could mediastinoscopy be in detecting level No. 7 metastases? This is quite a difficult station to pick up, especially when the mediastinal pleura is involved.
Dr Pilling: Absolutely. We have only just started to perform cervical mediastinoscopy. We have done 4 patients now. So we will be able to report our experience in due course. There was a paper by Schouwink in the Annals of Thoracic Surgery this year that reported a 93% accuracy rate for cervical mediastinoscopy in N2 disease in malignant pleural mesothelioma. They found that positive nodes were found after a negative cervical mediastinoscopy in 6 of the 25 patients that they studied. So it will miss some patients. We think 88% would be accessible. So I think this is a tool which will allow us to avoid a hazardous operation on patients who probably shouldn't have it.
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