|Year : 2020 | Volume
| Issue : 5 | Page : 1082-1087
Biomembrane formation after radiofrequency ablation prevents bone cement extravasation during percutaneous vertebroplasty for treating vertebral metastases with posterior margin destruction: An animal study
Zhe Yu, Shilin Tian, Wei Wang, Yuliang Li, Yongzheng Wang
Department of Interventional Medicine, The Second Hospital of Shandong University, Institute of Tumor Intervention, Shandong University, Jinan, Shandong, China
|Date of Submission||15-Feb-2020|
|Date of Decision||20-Mar-2020|
|Date of Acceptance||22-Apr-2020|
|Date of Web Publication||29-Sep-2020|
Department of Interventional Medicine, The Second Hospital of Shandong University. Institute of Tumor Intervention, Shandong University, 247 Beiyuan Street, Jinan City, Shandong Province, 250033
Source of Support: None, Conflict of Interest: None
Aims: We aimed to investigate the feasibility, safety, and efficacy of radiofrequency ablation (RFA) combined with percutaneous vertebroplasty (PVP) for treating VX2 vertebral metastases with posterior margin destruction in a rabbit model.
Materials and Methods: Sixty rabbit models of VX2 vertebral metastases with posterior margin destruction were constructed through computed tomography (CT)-guided percutaneous puncture and randomly divided into four groups of 15 rabbits each: Groups A, RFA+PVP; B, PVP; C, RFA; and D, control. Five rabbits in each group were sacrificed within 24 h of the procedure. Pathological examination and immunohistochemical staining revealed the presence of a biomembrane barrier at the tumor edge; furthermore, bone cement leakage into the spinal canal was observed. The survival time of the remaining rabbits per group was observed, and the differences were analyzed.
Results: CT scans of Group A and C rabbits revealed a low-density band around the tumor ablation region. Bone cement leakage rate significantly differed between Groups A and B (20% vs. 100%; P < 0.05). The average postoperative survival times of Group A, B, C, and D rabbits were 16.72 ± 0.93, 7.26 ± 0.75, 7.80 ± 1.30, and 3.84 ± 1.24 days, respectively, showing a significant difference between Group A and the remaining groups (P < 0.05).
Conclusions: The biomembrane barrier formed at the tumor edge after RFA can prevent bone cement leakage into the spinal canal, reducing spinal cord injury and prolonging the survival time.
Keywords: Biomembrane barrier, percutaneous vertebroplasty, posterior vertebral margin destruction, radiofrequency ablation, VX2
|How to cite this article:|
Yu Z, Tian S, Wang W, Li Y, Wang Y. Biomembrane formation after radiofrequency ablation prevents bone cement extravasation during percutaneous vertebroplasty for treating vertebral metastases with posterior margin destruction: An animal study. J Can Res Ther 2020;16:1082-7
|How to cite this URL:|
Yu Z, Tian S, Wang W, Li Y, Wang Y. Biomembrane formation after radiofrequency ablation prevents bone cement extravasation during percutaneous vertebroplasty for treating vertebral metastases with posterior margin destruction: An animal study. J Can Res Ther [serial online] 2020 [cited 2020 Oct 26];16:1082-7. Available from: https://www.cancerjournal.net/text.asp?2020/16/5/1082/296430
| > Introduction|| |
Vertebral metastases occur in approximately 50%–70% of patients with advanced malignancies, and approximately half of these patients may experience posterior vertebral margin destruction.,,, Currently, the primary treatment modality for such patients is percutaneous vertebroplasty (PVP); however, in case of an incomplete posterior margin of the vertebral body, bone cement may leak into the spinal canal after PVP, causing severe damage to the spinal cord and even death. We sought to devise a method to form a barrier that would prevent bone cement leakage into the spinal canal when the posterior vertebral margin is damaged, thereby reducing spinal cord injury. We have previously used intraoperative radiofrequency ablation (RFA) or microwave ablation to demonstrate that a low-density band is formed around other tumors.,,, Thus, we hypothesized that a low-density band can be formed after thermal ablation of vertebral metastases. Our previous preliminary experiments have shown that a similar structure can be formed in the RFA treatment of vertebral metastases. This low-density layer, referred to as the biomembrane barrier, can potentially block bone cement extravasation, suggesting that RFA combined with PVP treatment can lead to favorable outcomes. To verify our hypothesis, we established an animal model of posterior vertebral margin destruction and confirmed the existence of the biomembrane barrier after RFA through imaging and pathological examination. Furthermore, we explored whether this barrier can prevent bone cement leakage into the spinal canal and reduce spinal cord injury.
| > Materials and Methods|| |
The study protocol was approved by the animal research committee of our institution and was conducted in accordance with the guidelines of the International Council on Animal Care. Seventy healthy New Zealand white male rabbits, weighing 3.0–3.5 kg, were purchased from Jinan Xilingjiao Biological Technology Co. Ltd (Experimental Animal License Number: SCXK Lu 2015 0001). General anesthesia was induced through an injection of 3% pentobarbital at a dose of 30 mg/kg into the rabbit ear vein; this was done before inoculation, imaging examination, and treatment.
Preparation of VX2 tumor block
The VX2 tumor block (purchased from Beijing Beina Chuanglian Biotechnology Research Institute) was cut into small blocks, approximately 1.0 mm 3, and kept in normal saline for use.
Construction of a rabbit model of posterior vertebral margin destruction
The experimental rabbits were anesthetized and fixed in a prone position, and the skin on the left lower back was prepared for the procedure. The junction of the superior aspect of the L4 or L5 vertebral body and the left pedicle was identified as the puncture point using computed tomography (CT; 64-row spiral CT, Siemens, Sensation, Germany) localization. An 18-gauge coaxial introducer needle (Japan Co. Ltd.) was used to puncture the target vertebra under CT guidance, and the needle was advanced until it reached the center of the punctured vertebral body. Following this, the inner core of the trocar was used to coaxially push two tumor blocks into the vertebrae body through the sheathed needle, and a piece of Gelfoam (0.5 cm; Jinling Pharmaceutical Company, Nanjing, China) was used to seal the needle tract. CT and magnetic resonance imaging (MRI; 3.0 T Verio MRI machine, Siemens Company, Germany) were performed at 3–4 weeks postoperatively. The model was considered successful when the posterior vertebral cortex was destroyed [Figure 1].
|Figure 1: Vertebral metastases with posterior margin destruction model construction. (a) An 18-gauge coaxial introducer needle. (b) Positioning ruler is placed on the back of the rabbit during computed tomography. (c) Puncture needle tip is located in the middle of the vertebral body (white arrow). (d) Computed tomography scan shows that the posterior vertebral cortex is discontinued and the posterior margin of the vertebral body is destroyed. (e) Magnetic resonance imaging scan shows that the posterior margin of the vertebral body is destroyed by tumor (white arrow)|
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In total, 60 rabbits with posterior vertebral margin destruction were included and randomly divided into Groups A, B, C, and D, with 15 rabbits per group. After anesthesia induction, an 18-gauge RFA needle (Olympus Company) was inserted into the tumor center of Group A and C rabbits under CT guidance [Figure 2]a. This needle was connected to the RFA instrument, with the output power sequentially increased from 2 W–4 W. A timer was started when the temperature of the needle tip reached 95°C, and RFA was stopped after 1 min. In Group A, 0.4 ml bone cement (Italy Tecres SPA Company) was injected into the tumor center immediately after the ablation [Figure 2]b. In Group B, 0.4 ml bone cement was injected after anesthesia induction [Figure 2]c; in Group D (control group), only 0.4 ml normal saline was injected. Bone cement was injected approximately 2 min after its formulation at a ratio of 1:1.
|Figure 2: Intraoperative real-time imaging during radiofrequency ablation and percutaneous vertebroplasty (a). The ablation needle penetrates tumor center. (b) Bone cement injection after radiofrequency ablation, with no cement leakage into the spinal canal. (c) Bone cement leakage into the spinal canal after a single bone cement injection (the arrow)|
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Histology sampling and testing
Five rabbits from each group were sacrificed within 24 h of the procedure, and the diseased lumbar spines were removed and fixed in a 10% formaldehyde solution for 48 h. Following this, the spines were placed in a decalcifying solution for approximately 24 h until pins could be easily nailed into the vertebral body, indicating that the decalcification was complete. Tissue samples were obtained from the vertebral body specimens at a thickness of 8 mm. After processing in a dehydrator for 12 h, the sections were embedded in paraffin and cut into five continuous 5-μm-thick sections. These sections were stained with hematoxylin and eosin (H and E; Shanghai Lanji Technology Development Co. Ltd.) and Masson's trichrome (Zhuhai; Besso Biotechnology Co. Ltd.); furthermore, immunohistochemical staining was performed with vimentin (Maixin Biotechnology Co. Ltd.).
The survival times of the remaining ten rabbits in each group were observed and recorded. The maximum follow-up period was 3 weeks. The Statistical Package for the Social Sciences 24.0 software (version 24; SPSS, Chicago, IL, USA) was used for statistical analysis. The results were expressed as mean±standard deviation (x±sd). The overall difference between the groups was tested using independent samples t-test, and P < 0.05 was considered significant.
| > Results|| |
VX2 vertebral metastasis model was successfully constructed in 60 of the 70 rabbits at 3–4 weeks after VX2 tumor block implantation. The main reasons for the failure in ten rabbits were as follows: (1) four rabbits died of anesthesia due to the rapid injection rate of the anesthetic and (2) six rabbits were successfully inoculated with tumor blocks, but no tumor growth was observed 3–4 weeks after the inoculation due to the degeneration of the tumor block or the autoimmunity of the animals. The rabbits in which the model could not be constructed were excluded from the study. The success rate of modeling was 85.7%. Hind limb paralysis occurred in all 60 rabbits. The mean longest and shortest diameters of the tumor measured through MRI were 1.25 ± 0.24 cm and 0.93 ± 0.14 cm, respectively. Target vertebral puncture was successfully performed in all 60 rabbits. Groups A and B were injected with 0.4 ml bone cement, following which Group A exhibited a bone cement leakage rate of 20%. In all Group B rabbits, bone cement leaked into the spinal canal and invaded the spinal cord [Figure 2]c. Five rabbits from each group were sacrificed within 24 h of the procedure and vertebral tumor specimens obtained [Figure 3]. Specimens from each group were subjected to H and E and Masson's trichrome staining as well as immunohistochemical staining using vimentin. A biomembrane barrier was observed at the edge of the tumor in Groups A and C [Figure 4]; however, no biomembrane barrier was observed in Groups B and D. The bone cement had leaked into the spinal canal through the posterior margin of the damaged vertebral body, causing spinal cord injury in Group B [Figure 5] and [Figure 6].
|Figure 3: Postoperative gross specimens of Group A. Bone cement injected into the tumor (indicated by the arrow)|
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|Figure 4: Group A and C postoperative pathological sections. A dense cord band (black arrows) observed at tumor edge after radiofrequency ablation. (a) (H and E) staining (×20). (b) H and E staining (×40). (c) H and E staining (×100). (d) H and E staining (×200) (e) Masson's trichrome staining. (f) Vimentin staining|
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|Figure 5: Group B postoperative gross specimens. Bone cement leaking into the spinal canal and invading the spinal cord (indicated by the needle tip)|
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|Figure 6: Group B and D postoperative pathological sections. Growing cells destroy the bone cortex, grow into the spinal canal, and invade the spinal cord. (a) H and E staining. (b) Masson's trichrome staining (▴ vertebral cortex; ☆ vertebral cortical destruction; ○ tumor cells; ◊ spinal cord)|
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Statistical analysis showed that the mean postoperative survival times of Groups A, B, C, and D were 16.72 ± 0.93, 7.26 ± 0.75, 7.80 ± 1.30, and 3.84 ± 1.24 days, respectively [Figure 7]. The postoperative survival time of Group A was significantly different from those of the other three groups (P < 0.05). Moreover, there was a significant difference in the postoperative survival time between Groups B and D and Groups C and D (P < 0.05); however, the difference between Groups B and C was not significant (P = 0.27).
|Figure 7: Survival curve of the groups. Radiofrequency ablation combined with percutaneous vertebroplasty treatment can effectively improve the prognosis. Two rabbits were alive in Group A after 3 weeks, the maximum study observation time|
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| > Discussion|| |
The vertebral body is a common metastatic site of several malignant tumors, such as breast, lung, and prostate cancers.,,,, Morbidity due to malignant tumor spinal metastases in the late stages can occur in 30%–70% of patients. In addition, 70% of metastatic tumors can cause osteolytic damage, leading to pathologic fractures of the vertebral body and severe pain., The most common presenting symptom is persistent back pain that worsens at night and after exercise. These fractures can cause nerve dysfunction through spinal cord compression, which seriously affects patient survival and quality of life. Therefore, the treatment of spinal metastases is focused on controlling tumor growth, increasing bone stability, increasing analgesic effects, and preventing neurological symptom development.
The current treatment modalities for spinal metastases include radiation, chemotherapy, targeted drugs, open surgery, and minimally invasive interventional therapy.,,, With the recent rapid development of technology, minimally invasive interventional therapy has become increasingly common in the treatment of bone metastases. The current interventional therapies for the treatment of bone metastases include PVP, RFA, brachytherapy with radioactive iodine-125, photodynamic therapy, cryoablation, and transarterial chemoembolization.,,,,,,,, Each therapy has its advantages and disadvantages. With the recent improvements in interventional techniques, PVP and RFA have become increasingly popular in the treatment of vertebral metastases. Some researchers believe that a combination of PVP and RFA can produce complementary effects and significantly improve therapeutic outcomes; however, this technique requires the posterior vertebral margin to be intact, and unfortunately, the margin is often found to be already damaged at the time of consultation. At present, the use of either PVP or RFA alone has certain limitations: PVP alone can lead to bone cement leakage into the spinal canal, causing severe injury to the spinal cord or even paralysis; similarly, RFA alone is not available for complete ablation because the tumor frequently invades the spinal cord. Therefore, it is prudent to find a safe and effective minimally invasive interventional therapy to relieve pain and control tumor growth in the affected patients so as to provide new ideas and approaches for the treatment of patients with vertebral metastases with posterior vertebral margin destruction.
In this study, we constructed a rabbit model of VX2 vertebral metastases with posterior margin destruction. We confirmed that a layer of dense cord can be formed at the edge of the tumor after RFA and defined this layer as a “biomembrane barrier;” we found that this biomembrane barrier can prevent bone cement leakage into the spinal canal during PVP, thereby reducing spinal cord injury. This provides an important theoretical basis for the treatment of vertebral metastases with posterior margin destruction caused by various tumors. We performed Masson's trichrome and vimentin staining (specific for fibrous connective tissue) of the biomembrane barrier. Our results also confirm that using these two stains, a layer of low-density bands can be detected at the tumor edge after RFA; these findings preliminarily prove that the biomembrane barrier may be a layer of fibrous connective tissue. We speculate that RFA can stimulate fibroblasts around the tumor, causing their rapid proliferation that leads to the formation of a layer of dense fibrous bands. Due to its density and thickness, this layer can prevent postinjection bone cement leakage into the spinal canal. The signaling pathways involved in stimulating fibroblast proliferation after RFA and the specific composition of this biomembrane remain unknown and are an area of active research within our group. We also analyzed the differences in survival times among the groups. Our data show that RFA combined with PVP treatment can effectively improve prognosis because two rabbits were still alive after 3 weeks of the procedure. This was the upper limit of our observation time in the study. Although PVP and RFA alone can also improve prognosis, their individual benefits are limited compared with those of a combination treatment. The mortality rate in Group B on the first and second days was equivalent or even worse than that in the control group. We attribute this to bone cement extravasation, leading to spinal cord injury and accelerating death. Electrolyte disorder due to urinary retention and intestinal obstruction was considered to be the main cause of death in the animals because the rabbits had urinary retention in the early stages after successful modeling, which was confirmed through imaging and catheterization. If no intervention was provided during this early period, tumor growth would have destroyed more spinal cord tissue and caused intestinal obstruction. When intestinal obstruction occurred, rabbits would eat little or even nothing, which can lead to severe electrolyte imbalance and death. Group A, B, and C rabbits received intervention at an early stage, which slowed the tumor growth. Therefore, the survival rate was much better and the occurrence of intestinal obstruction was much lower in these three groups than in Group D.
In summary, using our rabbit model, we proved that RFA combined with PVP is more likely to prolong survival than RFA or PVP alone in the treatment of vertebral metastases with posterior margin destruction.
| > Conclusions|| |
A biomembrane barrier at the edge of the tumor is formed after RFA in a rabbit model of VX2 vertebral metastases with posterior margin destruction; this barrier can prevent bone cement leakage into the spinal canal, reducing spinal cord injury and prolonging the survival time. This novel attempt may provide a new theoretical basis and practical support for the interventional treatment of patients with vertebral metastases with posterior margin destruction. RFA combined with PVP is expected to be used in a clinical study of nonvascular interventional therapy for vertebral tumor with posterior margin destruction.
This work is supported by the Shandong Province Key Research and Development Plan (Grant No. 2019GSF108105), National Natural Science Foundation of China (NSFC, Grant No. 6167276, 11971269), and Shandong Province Integrated Traditional Chinese and Western Medicine Special Disease Prevention Project (Grant No. S190009280000).
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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