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J Thorac Cardiovasc Surg 2002;124:486-492
© 2002 The American Association for Thoracic Surgery
General Thoracic Surgery (GTS) |
From the Departments of Thoracic Surgerya and Pathology,b Saiseikai Central Hospital, Tokyo, Japan.
Received for publication Nov 7, 2001. Revisions requested Feb 5, 2002; revisions received Feb 28, 2002. Accepted for publication March 6, 2002. Address for reprints: Hiroaki Nomori, MD, Department of Thoracic Surgery, Saiseikai Central Hospital, 1-4-17 Mita, Minato-ku, Tokyo 108-0073, Japan (E-mail: hnomori{at}qk9.so-net.ne.jp).
| Abstract |
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| Introduction |
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Recently, identification of sentinel lymph nodes with a radioisotope tracer with or without isosulfan blue dye has been used during surgery for melanoma, breast cancer, and gastrointestinal cancers, with an accuracy greater than 80%.
8-10 In lung cancer surgery, Little and colleagues
11 demonstrated the identification rate of sentinel lymph nodes in fewer than 50% of patients with isosulfan blue dye, because intrathoracic lymph nodes were usually black, which made the blue dye method inaccurate. Recently Liptay and associates
12 used a technetium Tc 99m sulfur colloid and reported that the identification rate for sentinel lymph nodes was 82% and the accuracy was 95%. In this study, sentinel lymph nodes were identified with technetium Tc 99m tin colloid in patients with NSCLC undergoing curative resection with mediastinal lymph node dissection. The accuracy and usefulness of this method for effective lymph node dissection and sampling were determined.
| Material and methods |
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Administration of radioactive colloid
Under Japanese law, the radioisotope could only be injected in a radioisotope room. A radioisotope tracer was therefore injected according to the following procedure: (1) in the computed tomography room, the site for radioisotope injection was marked on the skin and the angle and depth of the needle required to reach the peritumoral region was determined (Figure 1); (2) the day before surgery, in the radioisotope room, a 23-gauge needle was introduced from the marked point on the skin to the peritumoral region according to the angle and depth measured; (3) 6 to 8 mCi of technetium tin colloid suspended in a volume of 1 to 1.5 mL was injected with a single shot; and (4) lymphoscintigraphy was performed 5 minutes after the injection and the next morning just before surgery.
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Counting of radioactivity
The radioactivity in the lymph nodes was counted before (in vivo) and after (ex vivo) dissection with a handheld gamma probe (Navigator; Auto Suture Japan, Tokyo, Japan). The radioactivity count was recorded for a 20-second period. If there was incomplete fissure between the lobes, the in vivo radioactivity of the hilar lymph node stations was counted after dividing the fissure and exposing the lymph nodes.
Criteria for sentinel nodes
The lymph node nomenclature used was similar to the lymph node map for lung cancer reported previously (Table 1).
13 For in vivo counting, sentinel lymph nodes were identified as any node for which the count was 10 times the intrathoracic background value. For ex vivo counting, sentinel lymph nodes were defined as any node for which the count was 10 times the radioactivity of the resected lung tissue with the lowest count or the resected subdermal tissue. Finally, sentinel lymph nodes identified by ex vivo counting were determined to be the true sentinel lymph nodes, because in vivo counting could include radioactivity from the primary tumor.
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Correlation between in vivo and ex vivo counting
To clarify the accuracy of in vivo sentinel lymph node identification, the correlations for both hilar and mediastinal lymph node stations between in vivo and ex vivo results were examined.
Statistical analysis
The Fisher exact test for nominal variables was used to compare successful sentinel lymph node identification according to the patient's age, sex, ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC), tumor location, and pathologic N stage. The other data were analyzed for significance with the 2-tailed Student t test.
| Results |
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1.9 x 10-9).
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Step sections and immunohistochemical examination revealed micrometastasis in 1 of the 63 sentinel lymph nodes (2%), without metastasis in the routine hematoxylin and eosin-stained sections. This result did not change the tumor stage in that patient.
Whereas the relationship between in vivo and ex vivo results for the hilar lymph node stations showed concurrence in 20 patients (50%) for the hilar lymph nodal stations, 35 patients (88%) showed concurrence for the mediastinal lymph node stations; this difference was statistically significant (P = .0003). Of the 5 patients who did not show a correlation in the mediastinal lymph node stations, 1 appeared to have an additional sentinel lymph node on ex vivo counting, whereas the sentinel lymph nodes identified by in vivo counting in the other 4 were judged not to be sentinel lymph nodes by ex vivo counting.
| Discussion |
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Liptay and associates
12 identified sentinel lymph nodes in lung cancer after intraoperative injection of 99mTc sulfur colloid with a particle size of approximately 40 nm diameter. The particles of 99mTc tin colloid, on the other hand, are much larger than those of a 99mTc sulfur colloid, about 1000 nm in diameter, and should therefore take longer to reach the sentinel lymph nodes than the 99mTc sulfur colloid. As shown in Figure 2
, it took several hours for sufficient 99mTc tin colloid to reach the sentinel lymph nodes. Although the optimum particle size for the radioisotope tracer for sentinel lymph node identification in lung cancer patients has not been clarified, we believe that 99mTc tin colloid would be more suitable than 99mTc sulfur colloid for the following reasons. First, 99mTc sulfur colloid can reach the sentinel lymph nodes rapidly, because of its small particle size, but could pass through the true sentinel lymph nodes and flow further up the chain of nodes, resulting in false-negative results. Actually, it has been reported that the hottest node with 99mTc sulfur colloid is not always the sentinel lymph node in patients with melanoma.
14 On the other hand, a 99mTc tin colloid, because of its large particle size, could be lodged within the sentinel lymph nodes for a longer period than a 99mTc sulfur colloid, which could make the false negative rate lower. Second, unlike in other organs, radioisotope injected into the lung frequently leaks into the tracheobronchus, as shown in Figure 2
. This could make in vivo counting unreliable immediately after the injection. A 99mTc sulfur colloid procedure, because of its intraoperative injection, could result in the radioisotope tracer leaking into the tracheobronchus and make the radioactivity of lymph nodes around the tracheobronchus higher than the true value. On the other hand, because 99mTc tin colloid has to be injected a few hours before surgery, the material leaked into the tracheobronchus has been already washed out at surgery, resulting in more reliable in vivo counting. Finally, intraoperative injection of 99mTc sulfur colloid might not reveal the natural lymphatic flow because of the thoracotomy itself and intraoperative manipulation of lung. However, a comparison of our results with those of Liptay and associates
12 with 99mTc sulfur colloid revealed similar results: (1) the identification rate for sentinel lymph nodes was 82% by the method of Liptay and associates,
12 compared with 87% by our method; (2) mediastinal sentinel lymph nodes were found in 22% of patients by Liptay and associates
12 and in 35% in this study; and (3) false-negative results were observed in 5% of patients by Liptay and associates
12 and in none of our patients.
In the hilar lymph node stations, sentinel lymph nodes were identified most frequently in the lobar lymph node (No. 12). The reason for the lower frequency of sentinel lymph nodes in the interlobar (No. 11) and hilar (No. 10) lymph nodes can be explained by the fact that these nodes are located further away from the primary tumor than are the lobar (No. 12) nodes. However, although the segmental (No. 13) lymph nodes were located nearer to the primary tumor than the lobar (No. 12) nodes, the former were identified as sentinel lymph nodes less frequently than the latter. This observation is similar to those in previous reports, which demonstrated that lymph node metastases of lung cancer were more frequent in the lobar (No. 12) lymph nodes than in the segmental (No. 13) nodes.
4,15 We consider that this might be due to the following reasons: (1) some of the lymphatic flow passes through lymphatic vessels of the visceral pleura and goes to the lobar lymph nodes but not through the segmental nodes and (2) some of the lymphatic flow within the lung tissue goes directly to the lobar lymph nodes without passing through the segmental nodes.
Skip metastasis to the mediastinal lymph nodes has been reported to occur in 20% to 40% of patients with NSCLC,
4-6,15 which could be because some lymphatic flow from the lung goes directly to the mediastinum through the pleura and not to the hilar lymph node stations.
16 Our study showed that sentinel lymph nodes were identified in 35% of mediastinal lymph nodes, and that the lymphatic route to each mediastinal lymph node station was lobe specific; the lymphatic flow from the right upper lobe proceeds to the pretracheal or tracheobronchial lymph nodes, the left upper lobe to the Botallo node, and the lower lobe to the subcarinal node. This result is supported by previous reports, which showed a similar distribution of prevalence of mediastinal lymph node metastases from each lobe.
4-6,15
One of the potential benefits of sentinel lymph node identification is that pathologists can focus on fewer lymph nodes when identifying micrometastases by immunohistochemical assay or polymerase chain reaction. Izbicki and coworkers
17 used immunohistochemical methods and reported that 27% of patients with N0 and 45% with N1 staged from frozen tissue sections had micrometastases in the mediastinal lymph node stations, resulting in upstaging. However, both step sections and immunohistochemical assay for sentinel lymph nodes in this study showed micrometastases in only 1 of the 40 patients (3%). This could be because we examined formalin-fixed and paraffin-embedded tissue sections but not frozen sections alone.
There have been few reports comparing sentinel lymph node identification by in vivo and ex vivo counting, including other organ tumors. Although ex vivo counting is more accurate than in vivo counting, it is not practical for sentinel lymph node navigation surgery because it is only available after dissection. To be of practical use for sentinel lymph node navigation surgery, the in vivo counting data have to be accurate. We therefore examined the correlation between in vivo and ex vivo counting for both hilar and mediastinal lymph node stations. Our results indicated that whereas the hilar lymph node stations showed concurrence between the in vivo and ex vivo results in only 50% of patients, the mediastinal nodes showed concurrence in 88%. This could be because the mediastinal lymph node stations were less affected by "shine through" from the hot primary. Of the 4 patients with inconsistency between in vivo and ex vivo results for the mediastinal lymph node stations, only 1 showed an additional sentinel lymph node by ex vivo counting. That is to say, the rate of overlooking sentinel lymph nodes by in vivo counting of mediastinal lymph node stations was only 3% (1 of 40 patients). We therefore believe that sentinel lymph node identification by in vivo counting of mediastinal lymph node stations could be a useful approach to guide mediastinal lymph node sampling or dissection. We also recommend 99mTc tin colloid rather than 99mTc sulfur colloid for sentinel lymph node identification in lung cancer surgery, because in vivo counting by the former procedure could be less affected by the radioisotope leaked into tracheobronchus, as discussed previously.
How can sentinel lymph node biopsy change surgical procedures for NSCLC? First, it should be stated that sentinel lymph node identification is not practical for lung wedge resection, because the radioactivity of hilar lymph node stations cannot be determined by the wedge resection procedure. To evaluate the hilar lymph nodal stations, segmentectomy or greater resection is necessary. Second, we consider that sentinel lymph node biopsy could reduce systemic mediastinal lymph node dissection. For example, if all the dissected hilar lymph node stations and the mediastinal sentinel lymph nodes identified by in vivo counting showed no metastasis after lobectomy, mediastinal lymph node dissection would not be necessary. Third, sentinel lymph node identification could be useful as an indication for segmentectomy; after segmentectomy, if all the dissected hilar lymph node stations and mediastinal sentinel lymph nodes identified by in vivo counting revealed no metastasis, segmentectomy could be enough for curative resection, especially for small lung cancers. Okada and coworkers
18 reported that segmentectomy with mediastinal lymph node dissection for lung cancers less than 2 cm in size with clinical N0 stage carried a 5-year survival similar to that seen with lobectomy. Whereas their procedure required intraoperative pathologic diagnosis for all the dissected lymph nodes, including the mediastinal nodes, our procedure could reduce the number of lymph nodes examined during surgery.
Although sentinel lymph node biopsy was developed for breast cancer and melanoma, recent articles have demonstrated that this procedure has no advantage relative to elective lymph node dissection or sampling in patients with these diseases.
19,20 We therefore consider that further examination, including multicenter trials, is necessary to determine the role of sentinel lymph node identification in NSCLC.
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