Percutaneous Vertebral Augmentation and Thermal Ablation in Patients with Spinal Metastases

Abstract

Vertebral augmentation and thermal ablation offer radiologists a robust minimally invasive option for treatment of patients with spinal metastases. Such interventions are commonly combined and have proved safe and effective in the management of selected patients with vertebral metastases with durable treatment effects. Special attention to procedure techniques including choice of vertebral augmentation technique, choice of ablation modality, and thermal protection is essential for improved patient outcomes. This article provides a review of the most recent advances in vertebral augmentation and thermal ablation for the treatment of spinal metastases.

Keywords

interventional radiology - bone cancer - spine - vertebral augmentation - ablation - radiofrequency ablation

Cancer is the second most common cause of death in the United States, and according to the American Cancer Society, a substantial subset of new cancer patients are anticipated to develop spinal metastases.[1] Skeletal-related events in the setting of vertebral column metastases often adversely affect patient's functional independence and quality of life.[2] [3]

The important limitations of alternative treatment options for vertebral metastases include lack of timely and sufficient pain relief with external beam radiation therapy (gold standard treatment) in considerable subgroup of patients, sensitivity of the spinal cord to radiation affecting future treatment, considerably morbidity of surgical interventions, the often-inadequate response to systemic therapies as well as common side effects, and incomplete pain palliation with use of opioids.[4] [5] [6] Minimally invasive percutaneous vertebral augmentation and thermal ablation have been progressively incorporated in the management algorithm of patients with spinal metastases in the recent years with substantial published data supporting safety, efficacy, and durability of these interventions.[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] This article reviews the role of percutaneous vertebral augmentation and thermal ablation for the management of spinal metastases.

Treatment Goals and Patient Selection Guidelines

Vertebral augmentation and thermal ablation are performed to achieve the following goals in patients with spinal metastases: (1) pain palliation, (2) local tumor control, (3) fracture stabilization or prevention, or (4) cure (oligometastatic disease; fewer than five lesions).[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29]

The primary indications for percutaneous thermal ablation (often combined with vertebral augmentation) include unremitting pain, inadequacy of optimized or maximized radiation therapy to achieve local tumor control, contraindications to radiation therapy, or insufficient response to systemic therapies and opioids. The following clinical and imaging criteria are utilized in practice to determine patient eligibility for thermal ablation and/or vertebral augmentation: extent of pain, patient performance status, life expectancy, status of spinal stability (determined by spinal instability neoplastic score [SINS]), status of metastatic epidural spinal cord compression, and extent of visceral metastases.[7] [8] [9] [11] [12] [13] [14] [15] [16] [17] [18] [19] [33] [34]

The recently published ACR Appropriateness Criteria provides the following guidelines for the management of spinal metastases.[31] Thermal ablation and vertebral augmentation may be appropriate in patients with asymptomatic pathologic vertebral fracture with or without edema on MRI and are usually appropriate for patients with pathologic vertebral fracture with marked and worsening pain. In addition, the ACR Appropriateness Criteria suggests that such interventions may be appropriate in patients with pathologic vertebral fracture with spinal malalignment.[31]

Spinal instability is a relative contraindication for percutaneous thermal ablation depending on severity which is evaluated using the SINS.[34] Surgical consultation for potential tumor resection/debulking and stabilization is considered for SINS of 7 or higher.[34] Spinal metastases with central canal stenosis because of osseous retropulsion are commonly managed surgically[35]; however, in the absence of spinal cord compression, thermal ablation may be considered in patients who are not surgical candidates. Surgical intervention is typically considered in patients with spinal instability determined by the SINS (scores of 7 or greater) or in the presence of metastatic epidural spinal cord compression.[7] [8] [9] [11] [12] [13] [14] [15] [16] [17] [18] [19] [33] [34]

Vertebral Augmentation

Percutaneous vertebral augmentation entails polymethylmethacrylate (PMMA) injection into the spinal column to achieve pathologic fracture stabilization or prevention, bone consolidation, and pain palliation. Pain palliation following vertebral augmentation is achieved by a combination of diminished motion among pathologic fracture fragments and exothermic effects of PMMA polymerization (temperatures of up to 80 °C); however, this short-lived heat effect does not result in tumor necrosis at bone–PMMA interface.[14] [35] In the spinal column where compressive stress is dominant, vertebral augmentation is utilized for the treatment of osteolytic or mixed osteolytic–osteoblastic metastases, either as a standalone intervention or in combination with thermal ablation.[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] This intervention is typically performed in most patients with spinal metastases following thermal ablation, in the absence of neurologic compromise or spinal instability, to minimize the possibility of post-ablation fracture and for pathologic fracture stabilization.[8] [9] [10] [11] [13] [14] [17] [19] [24] [27] [28] VA may be performed as a standalone intervention for spinal metastases in patients with many osseous or visceral metastases.[21] VA may not be indicated after thermal ablation of posterior vertebral elements only or of lower sacral spine segments.

A systematic review with meta-analysis of the literature which included 2 randomized control trials, 16 prospective studies, 44 retrospective studies, and 25 case series involving 3,426 patients demonstrated clinically meaningful reduction in pain (using visual analog scale), Oswestry Disability Index, and Karnofsky Performance Score in patients with vertebral pathologic fractures treated with vertebral augmentation.[36] The authors concluded that cement leakage is common, but rarely symptomatic.[36] The CAFÉ randomized controlled trial that was included in this systematic review demonstrated that VA is effective as a standalone procedure to provide palliation by reducing pain and opioid usage while improving quality of life in a study of 134 patients.[37] In a retrospective single-center study, investigators treated 72 vertebral pathologic fractures with epidural tumor involvement in 51 patients and reported statistically significant pain palliation for 94, 86, and 92% of patients at 1-day, 1-month, and 1-year postprocedural intervals.[22] A single case of cauda equina syndrome as a major complication was reported.[22] Balloon kyphoplasty may improve the quality of tumor filling in spinal metastases. However, in cases with low risk of cement leakage, use of balloon kyphoplasty may decrease cement interdigitation into the surrounding trabecular matrix, conceivably compromising anchorage.[23] Kyphoplasty using a variety of spinal implants such as SpineJack, vertebral body stents, PEEK implant (Kiva system), and Screw Assisted Internal Fixation (SAIF) have been used for the treatment of vertebral pathologic compression fractures to restore vertebral body height, improve kyphosis, decrease osseous retropulsion, and improve central canal stenosis.[20] [38] Investigators successfully performed kyphoplasty with implants for 53 vertebral body fractures with posterior wall retropulsion (no neurologic compromise) in 51 patients and reported pre- and postprocedural mean posterior wall retropulsion of 5.8 and 4.5 mm, respectively (p < 0.001), and mean vertebral body height of 10.8 and 16.7 mm, respectively (p < 0.001).[20] The authors reported three new fractures at treated levels (follow up of 1–36 months) for which no intervention was determined necessary.[20] Anselmetti et al[38] successfully treated 40 patients with vertebral pathologic fractures utilizing the PEEK implant (Kiva system) and reported statistically significant pain palliation, improved functional status, and decreased opioid consumption 1 month following the procedure. The technical success rate was 100% and investigators reported asymptomatic cement leakage in 16.3% of patients.[38]

Thermal Ablation

Radiofrequency Ablation

Recently introduced bipolar as well as navigational and articulating radiofrequency (RF) electrodes offer important advantages which are critical for patient safety and treatment outcomes and facilitate treatment of vertebral metastases in challenging anatomical locations.[7] [8] [9] [10] [14] [17] [27] These benefits include electrode tip navigation supporting treatment of challenging-to-access lesions along the posterior central vertebral body, achieving larger ablation zones, and improving efficiency. Additional benefits include precise real-time intraprocedural monitoring of ablation volume made possible by built-in thermocouples, and bipolar technology eliminating the need for grounding pads[7] [8] [9] [10] [14] [17] [27] ([Fig. 1]). In addition, simultaneous bipedicular vertebral ablations are feasible using such electrodes resulting in larger, confluent, and coalescent ablation volumes.[9] [27] The primary indications for utilization of RFA for the treatment of spinal metastases include (1) primarily osteolytic or mixed osteolytic–osteoblastic metastases, (2) vertebral metastases with no or small extraosseous components, and (3) challenging-to-access lesions such as tumors along the posterior central vertebral body ([Fig. 1]). RFA is typically not considered as an option for the treatment of densely osteoblastic metastases as the relatively high impedance of such tumors may result in ineffectiveness of RFA.[39] In our practice, we recommend simultaneous bipedicular RFA for the management of vertebral metastases to treat the entire clinical target volume to achieve improved local tumor control rates and more durable pain palliation.[9] [40]

Fig. 1 A 72-year-old man with metastatic hepatocellular carcinoma and painful T10 metastatic lesion. Axial (a) and sagittal (b) T1-weighted fat-saturated contrast-enhanced MR images show enhancing bone marrow replacing metastatic lesion in the right side of T10 vertebral body involving the posterior vertebral body wall and extending to the right posterior elements (a and b, arrows). Radiofrequency ablation was performed for pain palliation and local tumor control using simultaneous bipedicular approach to treat the entire clinical target volume aligned with consensus recommendations of the International Spine Radiosurgery Consortium, for improved local tumor control rates and more durable pain palliation. Anterior-posterior (c) and lateral (d) fluoroscopic images during radiofrequency ablation show bipedicular placement of two electrodes with medial articulation of the distal segments to create confluent coalescent and overlapping ablation zones (c, arrows). Note the 5-mm distance between electrode tips (width of spinous process as reference) (c). The first ablation is performed along anterior vertebral body (not shown). Subsequently, the electrodes are retracted to treat posterior vertebral body and pedicles (d, arrow). Lateral fluoroscopic image (e) shows vertebral augmentation which was performed immediately following RFA for pathologic fracture prevention. Sagittal T1-weigthed fat-saturated contrast-enhanced MR image (f) obtained 3 months following treatment shows local tumor control with nonenhancing tumor cavity and thin enhancing granulation tissue along ablation zone margins (f, arrows). Note hypointense cement within vertebral body (f).

In the largest series published to date on RFA of spinal metastases,[27] Tomasian et al treated 266 metastatic lesions in 166 patients using navigational bipolar RF electrode system and reported statistically significant and durable pain palliation at 1-week, 1-month, 3-month, and 6-month posttreatment follow-up intervals with an overall local tumor control rate of 78.9%. The investigators reported a total complication rate of 3% (8/266) and major complication rate of 0.4% (1/266).[27] In a multicenter prospective clinical trial, investigators treated 87 patients with vertebral metastases and documented statistically significant pain palliation and improvement in quality of life up to 6-month posttreatment interval with adverse effects rate of 3%.[17]

Cryoablation

The latest cryoprobes, with relatively small gauges (up to 17-gauge), offer various ablation zone volumes which allow generation of ablation zones in close proximity to critical anatomical tissues.[11] [12] [14] [28] Cryoablation is commonly used to treat spinal metastases with the following features: (1) large tumors with complex geometry, (2) tumors with large soft-tissue components, (3) large tumors involving the posterior vertebral elements, (4) paravertebral soft-tissue metastases, and (5) osteoblastic metastases ([Fig. 2]). The advantages of cryoablation include (1) delineation of hypoattenuating ice ball on CT, (2) concurrent use of several cryoprobes to achieve additive overlapping ablation volume, and (3) less intraprocedural and periprocedural pain compared with heating-based ablation techniques.

Fig. 2 A 59-year-old woman with metastatic non-small cell lung cancer and painful L4 metastatic lesion. Axial (a) CT image shows osteoblastic metastatic lesion within right anterior L4 vertebral body (arrow). Cryoablation was performed for pain palliation and local tumor control. Axial CT images (b–d) during cryoablation show placement of a single cryoprobe within L4 vertebral body osteoblastic lesion (b, open arrow). Active thermal protection of spinal cord is performed with epidural injection of carbon dioxide (b and c, arrow). Passive thermal protection is performed by placement of a thermocouple within right L4–L5 neuroforamen for temperature monitoring (c, open arrow). Note hypoattenuating ice call within the prevertebral soft tissues (d, arrow). Ice ball is not discernable within the osteoblastic lesion.

In a retrospective study, Cazzato et al utilized cryoablation for the treatment of 105 spinal metastases in 74 patients (combined with cementation in 72.4% of tumors).[28] The investigator reported statistically significant pain palliation at 1-day and 1-month postprocedural follow-up intervals as well as the last available posttreatment follow-up (mean of 14.7 months, median of 6 months). Completely pain-free status was achieved at the last available follow-up in 53.1% of patients. The local tumor control rate was documented at 82.1% (mean follow up of 25.9 months, median of 16.5 months).[28] The total complication rate was 8.5% (nine patients including two major and seven minor complications).[28] In a retrospective single-center study, investigators utilized cryoablation to treat 31 vertebral metastases and reported 96.7% local tumor control rate, substantial pain palliation, and decreased opioid usage at 1-week, 1-month, and 3-month posttreatment follow-up intervals without major complications.[11]

Microwave Ablation

Microwave ablation may be utilized for the management of vertebral metastases that are not in close proximity to neural structures and is most beneficial for the treatment of spinal metastases with the following characteristics: (1) osteoblastic metastases and (2) large paraspinal tumors with complex geometry.

Microwave ablation is less susceptible to convective cooling and varying impedance of neoplastic tissue with consequent more uniform and larger ablation volumes as well as improved efficiency compared with RFA with no need for grounding pads.[13] [19] [26] [29]

In a single-center retrospective study, investigators treated 140 spinal metastases in 91 patients with microwave ablation (combined with vertebral augmentation) and reported statistically significant pain palliation and reduction in opioid usage up to 6 months following treatment, decreased disability scores as well as a local tumor control rate of 94.8% at 6-month follow-up.[29] Khan et al utilized microwave ablation to treat 102 vertebral metastases (and myeloma) and achieved substantial pain palliation up to 20- to 24-week posttreatment interval with a local tumor control rate of 97% at 20 to 24 weeks and complications in 2 patients.[13]

Thermal Protection

Passive and active thermal protection techniques may be utilized to minimize undesired thermal injury to spinal cord and spinal nerves.[7] [9] [11] [14] Passive techniques entail assessment of patient biofeedback during ablation under conscious sedation (most importantly heat-based ablations), real-time temperature monitoring by placing thermocouples in the epidural space and neuroforamina, monitoring motor- and somatosensory-evoked potentials with ablations under general anesthesia, as well as conducting electrostimulation of peripheral nerves for the evaluation of potential nerve injury.[7] [9] [11] [14] Active techniques can be used prophylactically and are considered when temperature reaches 45 °C (heat) or 10 °C (cold).[14] Such techniques include temperature modification surrounding the tissue at risk or thermal insulation utilizing pneumodissection (carbon dioxide) and hydro-dissection. Hydrodissection is achieved by injection of warm or cool liquid (such as normal saline and 5% dextrose in water) surrounding the structure at risk. Ionic solutions such as saline should be avoided during RFA to avoid creation of a plasma field and undesired ablation zone propagation. Liquid should be used cautiously during cryoablation to minimize the possibility of liquid freezing and nontarget thermal injury. Measures to minimize skin thermal injury include precise assessment of ablation zone size and geometry, active thermal protection of subcutaneous tissues, and surface application of warm saline during cryoablation.

Conclusion

Percutaneous vertebral augmentation and thermal ablation offer a minimally invasive approach for safe, timely, and efficacious treatment of a subset of patients with spinal metastases with durable effects.

Conflicts of Interest

J.W.J.: Consultant and medical advisory board—Boston Scientific, BD/Bard, Stryker, Varian.

A.T. and J.L.: None.

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Publication History

Article published online:
10 July 2024