Published online before print October 19, 2005, 10.1148/radiol.2373050234
(Radiology 2005;237:1068-1074.)
© RSNA, 2005
Radiofrequency Ablation of Metastatic Mediastinal Lymph Nodes during Cooling and Temperature Monitoring of the Tracheal Mucosa to Prevent Thermal Tracheal Damage: Initial Experience1
Takao Hiraki, MD,
Kotaro Yasui, MD,
Hidefumi Mimura, MD,
Hideo Gobara, MD,
Takashi Mukai, MD,
Soichiro Hase, MD,
Hiroyasu Fujiwara, MD,
Nobuhisa Tajiri, MD,
Yoshio Naomoto, MD,
Tomoki Yamatsuji, MD,
Yasuhiro Shirakawa, MD,
Shinya Asami, MD,
Hideki Nakatsuka, MD,
Motohiko Hanazaki, MD,
Kiyoshi Morita, MD,
Noriaki Tanaka, MD and
Susumu Kanazawa, MD
1 From the Departments of Radiology (T.H., K.Y., H.M., H.G., T.M., S.H., H.F., N. Tajiri, S.K.), Gastroenterological Surgery, Transplant, and Surgical Oncology (Y.N., T.Y., Y.S., S.A., N. Tanaka), and Anesthesiology and Resuscitology (H.N., M.H., K.M.), Okayama University Medical School, 2-5-1 Shikatacho, Okayama 700-8558, Japan. Received February 11, 2005; revision requested April 11; revision received April 19; accepted June 1.
Address correspondence to T.H. (e-mail: takaoh{at}tc4.so-net.ne.jp).
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ABSTRACT
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Institutional review board approval and patient informed consent were obtained. Radiofrequency ablation in a total of 10 sessions was performed for each mediastinal lymph node metastasis from esophageal cancer that had a mean largest diameter of 2.2 cm ± 0.6 (standard deviation) in seven male patients (mean age, 59 years). During ablation, cooling and temperature of the tracheal mucosa were monitored in the proper position in eight of the 10 sessions; in the other two sessions, monitoring was not done because of tracheal stenosis (perforation resulted). Three of the four lymph nodes that were 2.0 cm or smaller in largest diameter showed no evidence of local progression for at least 1 year since ablation; all three of the nodes greater than 2.0 cm in largest diameter progressed within 6 months. The 1-year survival rate was 60%; the median survival time was 13 months. Radiofrequency ablation may be effective for local control of small metastatic mediastinal lymph nodes, and cooling and temperature monitoring of the tracheal mucosa in the proper position may prevent thermal tracheal damage.
© RSNA, 2005
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INTRODUCTION
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Recurrence is the most common cause of death for patients who undergo surgery for esophageal cancer and is thus considered a major prognostic factor (1,2). If lymph node recurrence is treated effectively, relatively long survival may be possible for selected patients (3–5). However, treatment of recurrent esophageal cancer is usually challenging because the previous therapies (including surgery, radiation, chemotherapy, and various combinations of these treatments) limit the options available for subsequent treatment. Radiofrequency (RF) ablation has been accepted as a minimally invasive therapy for tumors in a variety of organs (6–13). Thus, RF ablation might be a useful alternative as therapy for mediastinal lymph node metastasis from esophageal cancer, although to our knowledge it had not yet been investigated in the mediastinum. Potential advantages include favorable local tumor control, the freedom to perform the procedure regardless of any previous therapies, and the potential for repetition as needed (6–13).
RF ablation induces coagulation tissue necrosis by transfer of thermal energy (6–13). Tissue damage, however, may sometimes unfavorably occur in adjacent nontarget structures from excessive thermal conduction. The gastrointestinal tract, gallbladder, bile ducts, pleura, and diaphragm can be damaged when RF ablation is applied to hepatic tumors adjacent to such structures (14,15). Similarly, there is danger of the trachea being injured when RF ablation is applied to a mediastinal tumor adjacent to it. Thus, the purpose of our study was to evaluate RF ablation of metastatic mediastinal lymph nodes adjacent to the trachea in patients with esophageal cancer by using cooling and temperature monitoring of the tracheal mucosa during RF ablation.
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Materials and Methods
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From December 2002 to July 2004, seven patients underwent RF ablation of a metastatic mediastinal lymph node adjacent to the trachea with use of general anesthesia. During RF ablation, cooling and temperature monitoring of the tracheal mucosa were attempted to prevent thermal tracheal damage. The procedures were approved by our institutional review board, and written informed consent was obtained from all patients.
Patients and Lymph Nodes
The characteristics of the patients and lymph nodes are summarized in Table 1. Seven patients, all men (mean age, 59 years; range, 42–75 years), were enrolled in our study. Primary cancer in all patients was esophageal and was pathologically proved as squamous cell carcinoma. Treatment of the primary cancer was surgical resection combined with chemotherapy or chemoradiation therapy in six patients and chemoradiation therapy in one patient. The metastatic mediastinal lymph node was seen on routine follow-up computed tomographic (CT) images 3–15 months (mean, 9 months) after the first treatment of the primary cancer. According to our diagnostic criteria, lymph nodes are considered to be metastatic when they are larger than 1.0 cm in short-axis diameter. Our diagnosis was confirmed with pathologic proof at CT-guided needle biopsy before RF ablation in four patients. In all patients, each metastatic lymph node in the mediastinum was solitary. The mean size of the lymph nodes was 2.2 cm ± 0.6 (standard deviation) (range, 1.6–3.0 cm) in largest diameter. All lymph nodes were in contact with the trachea, and two were causing tracheal stenosis. All patients had recurrent laryngeal nerve palsy on the side where the metastatic lymph node existed. The metastatic mediastinal lymph node was the only evidence of metastatic disease in five patients. One patient had hematogenous metastasis in the liver, and one patient had hematogenous metastasis in the bone. Liver metastases regressed with intraarterial infusion chemotherapy administered through a catheter placed in the hepatic artery until RF ablation of the metastatic mediastinal lymph node. Bone metastasis located in a rib was also treated with RF ablation in the same ablation session as for the metastatic lymph node. Systemic chemotherapy was combined with RF ablation before and/or after RF ablation in six patients.
RF Ablation
Our indication criteria for RF ablation of metastatic mediastinal lymph nodes were as follows: (a) The metastatic lymph node was solitary in the mediastinum and the patient was not a candidate for surgical lymph node resection (n = 7) or (b) the metastatic mediastinal lymph node was the only evidence of recurrence (n = 5) or hematogenous recurrence was otherwise believed to be controllable with treatment at the time of RF ablation (n = 2). RF ablation was performed with curative intent in the five patients without hematogenous metastasis. In the two patients with hematogenous metastasis, RF ablation was performed in combination with treatment of the metastasis, in the hope of improving survival. A session was defined as one visit to the interventional CT suite where the lesion was treated. Four patients underwent one session; the other three underwent two sessions because the lymph node showed local progression after the first session. An RF application referred to placement of an RF electrode into the lesion and application of RF energy.
Patients were placed in the supine or prone position, and two standard steel mesh grounding pads were placed on the patients' thighs. Before RF ablation, CT images with 5 mm section thickness were obtained for targeting the area of interest. The entry site and path of the electrode were determined to avoid vital structures such as large vessels, lung, or reconstructed stomach, if possible. When this was not possible, insertion through the lung or reconstructed stomach was performed. Whenever possible, the electrode was planned to be positioned with the electrode shaft parallel to the longitudinal axis of the lymph node.
RF ablation was always performed percutaneously by two authors (T.H., K.Y., H.M., H.G., T.M.), each of whom had 4 years of experience with RF ablation. A single internally cooled electrode with a 1- or 2-cm noninsulated tip (Radionics, Burlington, Mass) was used for all ablations. The noninsulated tip length was determined on the basis of the size of the lymph node, that is, it was always equal to or smaller than the axis of the lymph node parallel to the electrode. The entry site of the electrode was the posterior chest wall in four sessions, the anterior chest wall in one session, and immediately above the jugular notch of the sternum in five sessions. The path of the electrode was through the lung in four sessions and through the subcutaneously reconstructed stomach in one. With CT (Asteion; Toshiba, Tokyo, Japan) fluoroscopic guidance, the electrode was advanced into the lymph node and positioned against its deepest margin. The average shortest distance between the electrode and the tracheal wall was 6.0 mm (range, 2.0–10 mm). The electrode was then attached to an RF generator (CC-1; Radionics) capable of producing a maximum output of 200 W. A peristaltic pump (Watson-Marlow, Medford, Mass) was used to infuse iced saline into the cooling lumen of the electrode at a rate sufficient to maintain a tip temperature below 20°C.
During RF application, tissue impedance was monitored continuously by means of circuitry incorporated in the generator, and an impedance-control algorithm was used. RF energy was applied with the average maximum power of 32 W (range, 15–80 W) for 6–12 minutes per RF application. The maximum power and time of RF application were determined on the basis of the physician's experience with RF ablation in the liver, lung, adrenal glands, and bone. In general, shorter time and lower power were used when the lymph node was smaller or overlapping ablations were adopted. The temperature of the lymph node at the electrode tip was measured immediately after the generator was turned off. When the temperature failed to reach 60°C, additional application at the same site was then required. The average temperature of the lymph node at the electrode tip was 64°C (range, 53°–79°C). When the noninsulated tip length was smaller than the axis of the lymph node parallel to the electrode, the electrode was withdrawn in increments of 5 mm for an electrode with a 1-cm noninsulated tip or increments of 1 cm for a 2-cm noninsulated tip, followed by application of RF energy. These were repeated until the expected coagulation length was beyond the axis of the lymph node. In one session, repositioning of the electrode from a different entry site was required after the electrode was completely removed in an attempt to ablate the entire lymph node. The mean number of RF applications per session was 2.8 (range, 1–6).
Cooling and Temperature Monitoring of the Tracheal Mucosa
Cooling and temperature monitoring of the tracheal mucosa were performed by two authors (H.N., M.H.) by using an endotracheal tube with a 7.0-mm inner diameter and an extra lumen for evacuation (Hi-Lo Evac; Mallinckrodt, Athlone, Ireland). As can be seen in Figure 1a, the evacuation lumen was used as a path for the thermocouple (Mon-a-Therm; Mallinckrodt, St Louis, Mo). The tip of the thermocouple was removed from the evacuation lumen through an opening in it and was attached to the surface of the inflated cuff on the side facing the lymph node with a piece of adhesive dressing (Tegaderm; 3M Health Care, St Paul, Minn) (Fig 1a).
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Figure 1a. (a) The endotracheal tube used for cooling and temperature monitoring of the tracheal mucosa. The thermocouple passes through the evacuation lumen (small arrows). The tip of the thermocouple (large arrow) extends from an opening (arrowhead) in the lumen and is attached to the surface of the inflated cuff with a piece of adhesive dressing. (b) Time curve of the temperature of tracheal mucosa measured with thermocouple. Before ablation, the temperature is decreased to 24°C. After RF application is initiated, the temperature increases rapidly to 33°C and then an exchange of saline decreases the temperature nearly to baseline. The temperature increase and subsequent decrease by saline exchange are repeated throughout RF application.
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At the beginning of the procedure, the endotracheal tube was introduced into the trachea. Whenever possible, the position of the tube was adjusted at CT fluoroscopy so that the cuff could be located at the level of the lymph node and so that the tip of the thermocouple faced the lymph node. The proximal end of the thermocouple was connected to the polygraph (LEG-1000; Nihon Kohden, Tokyo, Japan), which contained a computer processor, a screen to display real-time numeric temperature data and their time curve, and a recorder. The cuff was then inflated with chilled saline to cool the tracheal mucosa before ablation. Our goal was to maintain the temperature of the tracheal mucosa below 40°C throughout RF application. The saline inside the cuff was exchanged for fresh chilled saline whenever the temperature reached 33°–35°C (Fig 1b). The saline exchange was performed manually with deflation and reinflation of the cuff. In eight sessions, the endotracheal tube was positioned with the cuff located at the level of the lymph node, and cooling and temperature monitoring were subsequently performed at this level. In contrast, during the second session for two patients, the endotracheal tube could not be advanced until the cuff was located at the level of the lymph node because of tracheal stenosis. Thus, cooling and temperature monitoring were not performed in the proper position but rather at the level immediately cranial to the lymph node.
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Figure 1b. (a) The endotracheal tube used for cooling and temperature monitoring of the tracheal mucosa. The thermocouple passes through the evacuation lumen (small arrows). The tip of the thermocouple (large arrow) extends from an opening (arrowhead) in the lumen and is attached to the surface of the inflated cuff with a piece of adhesive dressing. (b) Time curve of the temperature of tracheal mucosa measured with thermocouple. Before ablation, the temperature is decreased to 24°C. After RF application is initiated, the temperature increases rapidly to 33°C and then an exchange of saline decreases the temperature nearly to baseline. The temperature increase and subsequent decrease by saline exchange are repeated throughout RF application.
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Immediately after RF ablation, an author (M.H.) with 15 years of bronchoscopy experience performed bronchoscopy to look for evidence suggesting thermal damage of the tracheal mucosa, including redness, edema, and erosion, in all patients but the two with tracheal stenosis.
Follow-up
According to our follow-up protocol, chest CT images were obtained each month before and after intravenous administration of contrast medium (iopamidol, Iopamiron 300; Nihon Schering, Osaka, Japan) for up to 6 months and then at 2- to 3-month intervals. Magnetic resonance imaging was used as an alternative in a patient with an allergy to iodine. Effectiveness of RF ablation was assessed by the presence of contrast enhancement in the lymph node: Lack of enhancement was deemed to indicate complete ablation and no evidence of local progression, while residual enhancement or appearance of the foci of enhancement in the lymph node that was previously considered to be completely ablated was deemed to indicate incomplete ablation or local progression, respectively. These radiologic assessments were achieved by consensus of two authors (T.H., K.Y., with 9 and 18 years of experience with chest imaging, respectively). The occurrence of complications and patients' outcome were evaluated by three authors (T.H., T.Y., Y.S.).
Statistical Analysis
The Fisher exact test was used to compare the incidence of local progression between the lymph nodes that were 2.0 cm or less in largest diameter and those greater than 2.0 cm. A difference with P < .05 was considered significant. Survival was calculated from the time of the first ablation by using Kaplan-Meier analysis. Statistical analysis was performed by using SPSS statistical software (version 11.0; SPSS, Chicago, Ill).
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Results
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Cooling and Temperature Monitoring of the Tracheal Mucosa
The tracheal mucosa was cooled to 24°–29°C before ablation (Fig 1b). After RF energy was applied, the temperature increased with variable speed (Fig 1b). After exchange of the saline, the temperature decreased nearly to baseline and then increased again until the next saline exchange; this was repeated throughout RF application (Fig 1b). Saline was exchanged six to 18 times during each application. Each saline exchange took approximately 30 seconds. The maximum temperature of the tracheal mucosa did not reach 40°C during any RF application. Bronchoscopy performed immediately after RF ablation revealed no obvious thermal damage of the tracheal mucosa.
Follow-up
The follow-up results are summarized in Table 2. Months are counted from the time of the first ablation session. The median duration of follow-up was 12 months (range, 7–18 months). In three patients, the ablation session was repeated because of local progression of the lymph node at 5, 3, and 4 months. In three of the four patients with a lymph node 2.0 cm or less in largest diameter, the lymph node showed no evidence of local progression and substantially decreased in size with one or two sessions for 12, 18, or 16 months, until the latest or last follow-up images (Fig 2). At the time of writing, two of these three patients are alive without evidence of recurrence at 18 and 16 months and one died of multiple hematogenous metastases at 12 months. The remaining lymph node with a largest diameter of 2.0 cm or less had seemed to be completely ablated, with substantial decrease in size, until 11 months, but then it showed local progression (Fig 3). The patient died of multiple hematogenous metastases at 13 months.
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Figure 2a. Metastatic mediastinal lymph node from esophageal cancer in a 60-year-old man. (a) Contrast material–enhanced transverse CT image obtained before ablation shows metastatic lymph node (arrow) of 1.8 cm in largest diameter in contact with the trachea in left superior mediastinum. Arrowhead = subcutaneously reconstructed stomach. (b) Transverse CT fluoroscopic image obtained during ablation shows the electrode (arrow) inserted into the lymph node immediately above the jugular notch of the sternum through the reconstructed stomach. Note the cuff inflated with saline (arrowheads) inside the trachea. The saline is contaminated by air bubbles. (c) Transverse contrast-enhanced CT image at 16 months shows the lymph node (arrow) decreasing in size without contrast enhancement, which indicates complete ablation.
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Figure 2b. Metastatic mediastinal lymph node from esophageal cancer in a 60-year-old man. (a) Contrast material–enhanced transverse CT image obtained before ablation shows metastatic lymph node (arrow) of 1.8 cm in largest diameter in contact with the trachea in left superior mediastinum. Arrowhead = subcutaneously reconstructed stomach. (b) Transverse CT fluoroscopic image obtained during ablation shows the electrode (arrow) inserted into the lymph node immediately above the jugular notch of the sternum through the reconstructed stomach. Note the cuff inflated with saline (arrowheads) inside the trachea. The saline is contaminated by air bubbles. (c) Transverse contrast-enhanced CT image at 16 months shows the lymph node (arrow) decreasing in size without contrast enhancement, which indicates complete ablation.
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Figure 2c. Metastatic mediastinal lymph node from esophageal cancer in a 60-year-old man. (a) Contrast material–enhanced transverse CT image obtained before ablation shows metastatic lymph node (arrow) of 1.8 cm in largest diameter in contact with the trachea in left superior mediastinum. Arrowhead = subcutaneously reconstructed stomach. (b) Transverse CT fluoroscopic image obtained during ablation shows the electrode (arrow) inserted into the lymph node immediately above the jugular notch of the sternum through the reconstructed stomach. Note the cuff inflated with saline (arrowheads) inside the trachea. The saline is contaminated by air bubbles. (c) Transverse contrast-enhanced CT image at 16 months shows the lymph node (arrow) decreasing in size without contrast enhancement, which indicates complete ablation.
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Figure 3a. Metastatic mdiastinal lymph node from esophageal cancer in a 57-year-old man. (a) Transverse CT fluoroscopic image obtained during ablation with patient in prone position shows the electrode inserted into the lymph node (arrows) along the vertebral body from the posterior chest wall. Note the cuff inflated with saline (arrowheads) inside the trachea. The saline is contaminated by air bubbles. (b) Transverse contrast-enhanced CT image at 9 months shows the lymph node (arrows) decreasing in size without contrast enhancement, which indicates complete ablation. Arrowhead = lung metastasis. (c) Transverse contrast-enhanced CT image at 11 months shows the lymph node (arrows) enlarging with contrast enhancement, which indicates local progression. Arrowhead = lung metastasis.
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Figure 3b. Metastatic mdiastinal lymph node from esophageal cancer in a 57-year-old man. (a) Transverse CT fluoroscopic image obtained during ablation with patient in prone position shows the electrode inserted into the lymph node (arrows) along the vertebral body from the posterior chest wall. Note the cuff inflated with saline (arrowheads) inside the trachea. The saline is contaminated by air bubbles. (b) Transverse contrast-enhanced CT image at 9 months shows the lymph node (arrows) decreasing in size without contrast enhancement, which indicates complete ablation. Arrowhead = lung metastasis. (c) Transverse contrast-enhanced CT image at 11 months shows the lymph node (arrows) enlarging with contrast enhancement, which indicates local progression. Arrowhead = lung metastasis.
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Figure 3c. Metastatic mdiastinal lymph node from esophageal cancer in a 57-year-old man. (a) Transverse CT fluoroscopic image obtained during ablation with patient in prone position shows the electrode inserted into the lymph node (arrows) along the vertebral body from the posterior chest wall. Note the cuff inflated with saline (arrowheads) inside the trachea. The saline is contaminated by air bubbles. (b) Transverse contrast-enhanced CT image at 9 months shows the lymph node (arrows) decreasing in size without contrast enhancement, which indicates complete ablation. Arrowhead = lung metastasis. (c) Transverse contrast-enhanced CT image at 11 months shows the lymph node (arrows) enlarging with contrast enhancement, which indicates local progression. Arrowhead = lung metastasis.
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In three patients, every lymph node greater than 2.0 cm showed local progression within 6 months. One patient had no recurrence anywhere else but died of a massive hemorrhage due to the progressive lymph node at 9 months. The other two are alive without evidence of any other recurrence at 8 and 7 months. At 5 months, one of the two patients underwent stent placement for tracheal stenosis due to the progressive lymph node.
The difference in the incidence of local progression between patients with a lymph node 2.0 cm or less in largest diameter and those with a lymph node greater than 2.0 cm was not significant (P = .11). The 1-year survival rate was 60%; the median survival time was 13 months.
Complications
Complications (Table 2) included pneumothorax in two of four sessions that involved electrode insertion through the lung. Both pneumothoraces resolved spontaneously. Electrode insertion through the reconstructed stomach did not result in any sequelae. Horner syndrome developed in two patients. In the two patients in whom cooling and temperature monitoring could not be placed properly, tracheal perforation occurred after the second session (Fig 4). In these patients, CT images obtained at approximately 1 month demonstrated air leakage from a defect in the posterior wall (Fig 4). Air leakage was localized to the region around the trachea, probably because of extensive adhesion (Fig 4b), and thus there were no symptoms related to tracheal perforation. Thereafter, the trachea was opened to allow for tracheal tube placement in these two patients. No symptoms or radiologic evidence suggested tracheal perforation in the other patients.
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Figure 4a. Metastatic mediastinal lymph node from esophageal cancer in a 75-year-old man. (a) Transverse CT fluoroscopic image obtained during second ablation session shows the electrode (large arrow) inserted into the lymph node immediately above the jugular notch of the sternum. Note that the cuff (arrowheads) is not inflated inside the trachea at this level. Small arrow = feeding tube inside the reconstructed stomach. (b) Transverse contrast-enhanced CT image 1 month after second ablation shows air leakage (large arrow) from a defect in the posterior tracheal wall. The periphery of the lymph node (arrowhead) shows contrast enhancement, which indicates incomplete ablation. Small arrow = reconstructed stomach.
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Figure 4b. Metastatic mediastinal lymph node from esophageal cancer in a 75-year-old man. (a) Transverse CT fluoroscopic image obtained during second ablation session shows the electrode (large arrow) inserted into the lymph node immediately above the jugular notch of the sternum. Note that the cuff (arrowheads) is not inflated inside the trachea at this level. Small arrow = feeding tube inside the reconstructed stomach. (b) Transverse contrast-enhanced CT image 1 month after second ablation shows air leakage (large arrow) from a defect in the posterior tracheal wall. The periphery of the lymph node (arrowhead) shows contrast enhancement, which indicates incomplete ablation. Small arrow = reconstructed stomach.
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Discussion
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RF ablation has been shown to provide promising results for local tumor control in a variety of organs (6–13). Thus, we considered the possibility that RF ablation might be an alternative treatment for metastatic mediastinal lymph nodes. Especially for patients whose condition is unsuitable for surgical resection, RF ablation may provide an opportunity to achieve remission even after administration of chemoradiation therapy. In our study, there seems to be a tendency for better local control of lymph nodes with a largest diameter of 2.0 cm or less than of lymph nodes greater than 2.0 cm, although our group is too small to allow us to detect a significant difference. All three lymph nodes that showed no local recurrence after ablation were 2.0 cm or less. The other node that was 2.0 cm or less had regressed for 11 months before local progression developed. On the other hand, lymph nodes greater than 2.0 cm showed local progression in a short time. Some explanations can be offered for the limited coagulation volume: adjacent large arteries working as "heat sinks" and the cooling effect on the lymph node caused by cooling of the tracheal mucosa.
The following survival rates in patients with lymph node recurrence of esophageal cancer have been reported: a 1-year survival rate of 35% after recurrence in patients who underwent treatment of lymph node recurrence (4) and of less than 40% after recurrence among patients who underwent treatment of local-regional recurrence that mostly involved the lymph node (3), a median survival of 7 months after recurrence in patients with regional recurrence that mostly involved the lymph node (2), and a 10-month survival rate of 0% in patients with intramediastinal recurrence that mostly involved the lymph node (16). Although we recognize that our study was small and had limited follow-up periods, the survival rates seem promising compared with the aforementioned results. At the time of this writing, particularly encouraging is the outcome of two patients who are alive without evidence of recurrence for 16 and 18 months after ablation. For these patients, RF ablation has been a curative treatment so far. However, three of seven patients died during follow-up. Two of the three patients had hematogenous metastasis at the time of RF ablation, which resulted in death. This procedure might not contribute to prolonged survival in patients with hematogenous metastasis, even if it seems controllable at the time of RF ablation. On the other hand, the outcome of the patient who had no hematogenous metastasis but died of a massive hemorrhage due to the progressive lymph node might suggest that control of a metastatic mediastinal lymph node is important for improved survival in patients without hematogenous metastasis. Further study is warranted in appropriately selected patients to determine the ultimate role of this procedure in providing a survival advantage.
With regard to the practical utility of RF ablation, certain limitations remain to be resolved. The limited extent of coagulation necrosis outlines the need for continued efforts to increase coagulation volume. In contrast, the unintended extent of coagulation necrosis may be another limitation that needs to be overcome (14,15). Livraghi et al (15) reported that seven of 2320 patients developed gastrointestinal perforation after RF ablation of hepatic tumors. They found two factors related to thermal gastrointestinal damage: the proximity of the tumors to the gastrointestinal tract and adhesion between the liver and the gastrointestinal tract. All seven patients had a tumor within 1 cm of the gastrointestinal tract. Six of the seven patients had a history associated with risk for adhesion, such as abdominal surgery or chronic cholecystitis. For these reasons, we expected that thermal tracheal damage in our patients would also have been highly likely without the cooling of the tracheal mucosa, because all patients had both a lymph node directly adjacent to the trachea and a history of surgery or radiation. Indeed, tracheal perforation occurred when we were unable to correctly place cooling and temperature monitoring in two patients. In these patients, we performed RF ablation while recognizing the possible risk of damaging the trachea, because treatment of the lymph node, which evidenced the only recurrence and was deemed the major prognostic factor, was assumed to be necessary for improved prognosis. Our strategy was to counter thermal conduction with the cooling effect of chilled saline. Several articles (17–19) have described the use of chilled saline to prevent thermal bile duct injury during RF ablation of the liver. Raman et al (17) report that intraductal chilled saline perfusion significantly (P < .005) decreases the degree of bile duct injury in swine. A similar technique has been used in certain clinical cases, which resulted in a successful prevention of bile duct damage (18,19).
Cellular homeostasis is preserved at a temperature up to approximately 40°C (20). On the basis of this fact, thermal damage of the tracheal mucosa could be prevented if the temperature of the mucosa can be maintained below 40°C throughout ablation. In our study, chilled saline decreased the temperature of the tracheal mucosa below 30°C before ablation. After RF energy was applied, the conducted heat increased the temperature, and the saline inside the cuff was simultaneously warmed, thereby reducing its cooling effect. Alternative fresh-chilled saline cooled the tracheal mucosa nearly to baseline, countering the continuous thermal conduction.
Our techniques had limitations. General anesthesia was necessary. The temperature data were obtained at only one point, although thermal conduction may be unevenly distributed to the trachea. The use of multiple thermocouples might offer the ideal of the three-dimensional volumetric temperature data. Our technique could not be properly performed in the two patients with tracheal stenosis, which resulted in tracheal perforation. Stent placement for tracheal stenosis before RF ablation might have allowed us to perform our techniques properly. Cooling of the tracheal mucosa might be an obstacle for complete tumor necrosis, but undercooling can result in tracheal perforation.
Our study also had limitations with regard to interpretation of CT images of metastatic lymph nodes. Small lymph nodes without pathologic confirmation can be benignly reactive. However, the criteria we used offered 95% (553 of 581) specificity in diagnosis of metastatic lymph nodes from esophageal cancer (21). In addition, the outcome of RF ablation cannot be completely assessed according to the presence of enhancement in the lymph node, partly because enhancement of the metastatic lymph node from esophageal cancer is often not sufficiently clear to allow a judgment to be made. Decreased tumor size in short-term periods does not necessarily indicate complete tumor necrosis. To ensure complete tumor necrosis, absence of tumor growth must be confirmed in long-term follow-up.
In summary, we have demonstrated that RF ablation may hold promise for local control of small metastatic mediastinal lymph nodes from esophageal carcinoma and that cooling and temperature monitoring of the tracheal mucosa in the proper position may prevent thermal tracheal damage.
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FOOTNOTES
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Abbreviations: RF = radiofrequency
Authors stated no financial relationship to disclose.
Author contributions: Guarantors of integrity of entire study, all authors; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of final version of submitted manuscript, all authors; literature research, T.H., K.Y., Y.N., T.Y., Y.S., S.A., S.K.; clinical studies, all authors; statistical analysis, T.H., Y.N., T.Y., Y.S., S.K.; and manuscript editing, all authors
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S.-Y. Chiou, J.-B. Liu, and L. Needleman
Current Status of Sonographically Guided Radiofrequency Ablation Techniques
J. Ultrasound Med.,
April 1, 2007;
26(4):
487 - 499.
[Abstract]
[Full Text]
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ABSTRACT
INTRODUCTION
