This retrospective analysis was approved by the Institutional Review Committee of our hospital. Informed consent was waived owing to the retrospective nature of this study. Medical records including demographic pain scores and Oswestry disability index (ODI) scores were obtained and reviewed.
Patient
Overall, 67 patients (42 men, 25 women) with 85 vertebral metastases were treated with MWA and VA at our institution from June 2015 to June 2021. The mean age of patients was 62.2 years (range,18–82 years). In 67 patients, there were 38 thoracic vertebrae and 47 lumbar vertebrae. A total of 53 (79.1%), 13 (19.4%), and 2 (1.5%) patients had 1, 2, and 3 lesions, respectively. The baseline clinical characteristics of the patients are listed in Table 1.
Table 1
Baseline Characteristics of the Study Participants
Characteristics
|
No.
|
Percentage
|
Age
|
62.2(range:18–82)
|
|
Sex
|
|
|
Male
|
42
|
62.7%
|
Female
|
25
|
37.3%
|
Primary tumor
|
|
|
Lung cancer
|
16
|
23.9%
|
Esophageal cancer
|
12
|
17.9%
|
Breast cancer
|
10
|
14.9%
|
Stomach cancer
|
9
|
13.4%
|
Colorectal cancer
|
9
|
13.4%
|
Ovarian cancer
|
5
|
7.5%
|
Cervical cancer
|
3
|
4.5%
|
Liver cancer
|
3
|
4.5%
|
Preprocedural Evaluation
All patients underwent computed tomography (CT) and magnetic resonance imaging (MRI) scans of the lesions before the procedure, mainly to evaluate the location and scope of the lesions, the degree of damage to the posterior edge of the vertebral body, and the relationship with the epidural space and spinal cord.
According to the modified Epidural Spinal Cord Compression Scale proposed by Gang Sun, Bilsky, and Shimony, the degree of epidural invasion and spinal cord compression is classified as type A, B, and C [12, 16–17]. Type C was not included in this study. The height of the vertebral body was measured on the sagittal CT digital. This was compared to the adjacent vertebral body and used to calculate the percentage of vertebral body compression. Neurological level of injury was sub-divided into levels A, B, C, D, and E according to the Frankel scale [18].
The visual analog scale (VAS) (range 0–10) was used to assess the patient’s pain before procedure. The pain of patients with multiple metastatic sites was recorded as the highest VAS score. Before the procedure, the patient s’ filled out ODI questionnaire was used to assess their quality of life.
Inclusion Criteria
We included patients with the following: (1) Thoracolumbar metastasis confirmed by pathology of the primary tumor.
(2) Persistent or recurrent pain after radiotherapy or refusal of radiotherapy.
(3) Intractable, localized pain (VAS score ≥ 4 at all metastatic sites).
(4) Destruction of the posterior margin of the vertebral cortex or invasion of the spinal canal without compression of the spinal cord (type A or B).
(5) Grade E spinal cord Frankel function.
(6) Expected survival time of at least three months.
Exclusion Criteria
We excluded patients with the following:
(1) Non-correctable coagulation disorder (platelets < 50×109/L; international normalized ratio > 1.50).
(2) A posterior margin of the vertebral body that destroyed by tumor and compresses the spinal cord with neurological symptoms.( type C)
(3) Spinal cord Frankel function ≤ Grade D.
(4) An Eastern Cooperative Oncology Group performance status of 3.
Procedural Details
All procedures were performed by the same interventionalist with > 10 years of experience in ablation treatment. An interdisciplinary team of radiologists, pain physicians, surgeons, and oncologists evaluated all patients before procedure. All procedures were completed under CT guidance.
The patient would lay prone on the CT bed and fixed with a vacuum negative pressure pad to prevent their movement during the procedure. We used a 3–5 mm CT scan to reconfirm the location of the lesion and measure the needle angle and depth. Throughout the procedure, patients were under moderate sedation with continuous intravenous infusion of sufentanil (50 ug/mL diluted 1:10 with saline solution) and local anesthesia by 20 g × 20 cm puncture needle (2% lidocaine hydrochloride and 0.25% ropivacaine hydrochloride). If the tumor was located on one side of the vertebral body and did not exceed the midline of the vertebral body, a unilateral pedicle puncture was used; otherwise, a bilateral pedicle puncture was used.
There were 23 cases of unilateral pedicle puncture of the vertebral body and 62 vertebral bodiessubjected to bilateral pedicle puncture. The bone puncture needle (13 gauge×130mm, Shandong Guanlong Medical Utensils Co., Ltd. Jinan, China) was inserted into the front edge of the vertebral body lesion, and three-dimensional reconstruction was employed to adjust the direction of the puncture needle.
We used the coaxial method to advance the MWA antenna (1.6mm×200mm, ECO Microwave Electronic Institute) along the bone puncture needle to the anterior edge of the tumor, and the bone puncture needle was withdrawn to expose the microwave antenna by at least 1.5–2.0 cm. We then inserted the temperature measuring electrode (20 gauge×200mm, ECO Microwave Electronic Institute) into the ipsilateral intervertebral foramen. The appropriate ablation power and time to perform ablation were selected. We closely monitored the temperature measurement of the electrode during the ablation process, and we terminated the ablation once the temperature exceeded 44°C[19]. During the ablation process, patients were constantly asked for any abnormal sensation and movement in their upper and lower extremities. If there was severe pain sensation and abnormal movement, the ablation was stopped immediately.
The MWA power was set between 20 and 40W (mean 30.5W, SD 5.4W), which was applied for 2-5min (mean 3.4min, SD 1.4min). Ablation power and duration were chosen according to the lesion. If the lesion was close to the front of the vertebral body, the ablation power was 30–40 W for 3–5 min. Whereas if the lesion was close to the back of the vertebral body, the ablation power was 20–30 W for 2–3 min. After the ablation was completed, the microwave antenna was withdrawn, and the bone puncture needle was advanced again to tumor’s front edge.
The polymethylmethacrylate bone cement (Osteopal V; Heraeus) was extracted with a 1 mL syringe and put into ice brine to prolong the setting time of the cement. We waited 10 min for the vertebral body temperature to drop before injecting bone cement. To prevent extravasation of the bone cement, a CT scan was used to observe the distribution of the bone cement A single vertebral body was scanned each time, and the scanning time was approximately 3 s.
When the bone cement was close to the posterior edge of the vertebral body, we reduced the single injection dose of the cement to 0.3–0.5 mL. If the bone cement was found to overflow in the spinal canal or intervertebral foramen, we immediately stopped the injection. A CT scan and three-dimensional reconstruction were performed immediately after the injection was completed to observe and record the distribution and leakage of bone cement (Fig. 1). The mean volume of bone cement injected per lesion was 5.2mL (SD 2.2ML, range 2.0-8.5mL). Radiologic and operative characteristics are listed in Table 2
Table 2
Radiologic and Operative Characteristics
Characteristics
|
No.
|
Percent/Range
|
Metastatic area
|
|
|
Thoracic
|
38
|
44.7%
|
Lumbar spine
|
47
|
55.3%
|
Type
|
|
|
Lytic
|
60
|
70.6%
|
Mixed
|
17
|
20.0%
|
Osteogenesis
|
8
|
9.4%
|
Compression fracture
|
|
|
Compression fracture
|
38
|
44.7%
|
Non-compression fracture
|
47
|
55.3%
|
Spinal segment
|
|
|
1
|
53
|
79.1%
|
2
|
13
|
19.4%
|
3
|
2
|
1.5%
|
Epidural encroachment
|
|
|
Type A
|
52
|
61.2%
|
Type B
|
33
|
38.8%
|
Ablation power (W)
|
30.5(SD, 5.4)
|
20–40
|
Ablation time (min)
|
3.4(SD, 1.4)
|
2–5
|
Volume of cement for each vertebra (mL)
|
5.2(SD, 2.2)
|
2.0-8.5
|
Cement leakage
|
37/85
|
43.5%
|
intervertebral discs
|
13
|
|
spinal canal
|
12
|
|
paravertebral
|
9
|
|
retrovertebral veins
|
2
|
|
intervertebral foramen
|
1
|
|
Technical success was defined as the accurate placement of the antenna in the lesion, achievement of the target ablation power and time, and placement of adequate cement in the lesion.
Follow-up Schedule
All patients undergoing MWA and VA completed a preprocedure evaluation and were followed up 24 h, 1 week, and 4, 12, 24 weeks after the procedure. The patients personally filled out a questionnaire to record their VAS scores and ODI scores. CT and MRI of the target vertebral bodies were performed to evaluate the local control of vertebral tumors at 4, 12, 24 weeks after the procedure. Local tumor progression was defined as the growth of an osteolytic defect or a soft tissue component of the tumor.
Outcome Assessment
Before the implementation of MWA and VA, each patient self-evaluated their pain score from 0–10 according to the VAS scoring standard. The patient's VAS score was reevaluated again at follow up point after procedure and compared to the preprocedure score. The treatment effect was evaluated according to the change in the pain score. The ODI scores were evaluated before the procedure and 4, 12, and 24 weeks after procedure, and the improvement of the patient’s quality of life and mobility was evaluated according to the changes in ODI scores.
The bone cement leakage during the procedure was evaluated based on the CT scan immediately after the procedure, and we recorded whether the bone cement spilled out, the location of the spill, and whether it was associated with neurological symptoms. The complications of MWA and VA were evaluated according to the Society of Interventional Radiology SIR evaluation criteria[20].
Statistical Analysis
All data analysis was performed using GraphPad Prism software, version 6.0 (GraphPad Software, La Jolla, California). Numerical data were expressed as means and SD or as medians and ranges, as appropriate. Qualitative data were expressed as frequencies and percentages. The analyses of changes in VAS score and ODI score before and after treatment were tested by Student t-tests. A P value < 0.05 was considered statistically significant.