Radiofrequency ablation of spinal tumors: temperature distribution in the spinal canal

Percutaneous radiofrequency ablation of primary intraosseous spinal glomus tumor

The glomus tumor is a rare, benign, but painful vascular neoplasm arising from the neuromyoarterial glomus. Primary intraosseous glomus tumor is even rarer, with only about 20 cases reported in the literature so far, 5 of which involved the spine. Surgical resection is currently considered the treatment of choice. We herewith present an uncommon case of primary intraosseous spinal glomus tumor involving the right pedicle of the eleventh thoracic vertebra (T11). To our knowledge, this is the first case of primary intraosseous spinal glomus tumor successfully treated by percutaneous CT-guided radiofrequency ablation (RFA).

Bipolar radio frequency ablation of spinal neoplasms in late stage cancer disease: a report of three cases

STUDY DESIGN

Case report.

OBJECTIVE

To avoid neuronal damage by using the bipolar radio frequency ablation of spinal tumors.

SUMMARY OF BACKGROUND DATA

Radio frequency ablation of tumorous masses is an established procedure and is increasingly used as pain therapy of unresectable spine tumors. Ablation of lesions adjacent to vulnerable structures remains a challenging task because flow of current is insufficiently controlled by monopolar probes. Using this technique, a prediction of the induced necrosis accurate to the millimeter is not feasible.

METHODS

Three patients with metastases of the spine were treated using the bipolar radio frequency ablation.

RESULTS

In all 3 cases collateral damage of neuronal structures could be avoided even though tumorous masses touched the cauda equina or were very close to vulnerable structures, respectively. The induction of necrosis was predictable to the millimeter.

CONCLUSION

Ablation of tumorous masses adjacent to neural structures by bipolar technique, is feasible and predictable. Spinal cord damage can be avoided by exact planning of the induced necrosis.

Osteoid osteoma of the mobile spine: surgical outcomes in 81 patients

STUDY DESIGN

A restrospective review of 81 cases of osteoid osteoma of the mobile spine submitted to surgical treatment.

OBJECTIVE

Analyze pro and contras of different techniques (conventional and minimally invasive) for the treatment of osteoid osteoma.

SUMMARY OF BACKGROUND DATA

Intralesional excision has been considered the standard treatment for spinal osteoid osteoma. The high success rate of minimally invasive surgery in the treatment of a variety of spinal disorders lead us to believe this technique can also be applicable for the treatment of osteoid osteoma of the spine.

METHODS

Eighty-one patients affected by osteoid osteoma were consecutively treated by the same team with intralesional excision using conventional or minimally invasive approach by video-assisted endoscopy, microscope, or percutaneous radiofrequency coagulation. The clinical features, the radiologic findings, and the outcome were reviewed. Pain and neurologic symptoms, were scored before surgery, after surgery and at the follow-up. Complications and local recurrences were also recorded.

RESULTS

Immediate relief of pain was observed after surgery in all patients. One patient showed mild neurologic impairment before treatment but became free of neurologic symptoms postoperative. Five local recurrences were found in four patients, always associated with pain. Three of these patients underwent surgery for a second time and one patient for a third time. There were two complications because surgery in two patients. One patient developed a pneumothorax, the other a hematoma. No related cases of kyphosis or scoliosis surgery were observed.

CONCLUSION

Conventional excision therapy is a effective and reliable treatment for osteoid osteoma associated to low morbidity and low local recurrence rate. Minimally invasive surgery is emerging as an alternative method, reducing soft tissue trauma and the collateral damage caused by traditional surgical approach, allow patients a more rapid and complete return to normal function.

Rupture of benign thyroid tumors after radio-frequency ablation

Rupture of benign thyroid tumors after RFA is very rare. We experienced 6 cases in 4 institutions. All patients presented with abrupt neck swelling and pain between 9 and 60 days after RFA. Imaging and clinical findings of the ruptured tumors were anterior subcapsular location, mixed composition, large size, and repeated ablations. Conservative treatment was sufficient in 3 cases, whereas surgical management was required in 3.

Palliative interventions for pain in cancer patients

Pain is a debilitating problem that is common to most patients with cancer at some time during the course of their disease. Conventional therapies such as opiate analgesics and radiation therapy provide suboptimal and limited relief. Novel image-guided interventions have made a significant impact in the management of this difficult problem. This article reviews some of the most promising image-guided techniques for relieving bone and visceral pain in patients suffering from cancer.

Percutaneous bone tumor management

Interventional radiology plays a major role in the management of bone tumors. Many different percutaneous techniques are available. Some aim to treat pain and consolidate a pathological bone (cementoplasty); others aim to ablate tumor or reduce its volume (sclerotherapy, thermal ablation). In this article, image-guided techniques of primary and secondary bone tumors with vertebroplasty, ethanol injection, radiofrequency ablation, laser photocoagulation, cryoablation, and radiofrequency ionization (coblation) will be reviewed. For each modality, the principles, the indications, and the results will be presented. The technical choice depends on the therapeutic intent-curative or palliative-and the need for consolidation, but also on the general status of the patient and the other therapeutic options. For the most complex cases, combined treatments can be required. However, the less disabling technique should always be considered first.

Radiofrequency ablation of a spinal osteoid osteoma: low heat-load technique

The present report describes successful radiofrequency ablation of a small osteoid osteoma in the second lumbar (L2) pedicle of a 10-year-old boy who had been experiencing several months of back pain. The lesion had no cortical bone separation from the spinal canal contents and was positioned immediately adjacent to a synovial facet joint. Treatment involved a low heat-load technique to avoid damage to nearby sensitive structures. The adjacent epidural space was monitored for temperature increase.

Percutaneous computed tomography fluoroscopy–guided conformal ultrasonic ablation of vertebral tumors in a rabbit tumor model

Object

Radiofrequency ablation (RFA) has proven to be effective for treatment of malignant and benign tumors in numerous anatomical sites outside the spine. The major challenge of using RFA for spinal tumors is difficulty protecting the spinal cord and nerves from damage. However, conforming ultrasound energy to match the exact anatomy of the tumor may provide successful ablation in such sensitive locations. In a rabbit model of vertebral body tumor, the authors have successfully ablated tumors using an acoustic ablator placed percutaneously via computed tomography fluoroscopic (CTF) guidance.

Methods

Using CTF guidance, 12 adult male New Zealand White rabbits were injected with VX2 carcinoma cells in the lowest lumbar vertebral body. At 21 days, a bone biopsy needle was placed into the geographical center of the lesion, down which an acoustic ablator was inserted. Three multisensor thermocouple arrays were placed around the lesion to provide measurement of tissue temperature during ablation, at thermal doses ranging from 100 to 1,000,000 TEM (thermal equivalent minutes at 43°C), and tumor volumes were given a tumoricidal dose of acoustic energy. Animals were monitored for 24 hours and then sacrificed. Pathological specimens were obtained to determine the extent of tumor death and surrounding tissue damage. Measured temperature distributions were used to reconstruct volumetric doses of energy delivered to tumor tissue, and such data were correlated with pathological findings.

Results

All rabbits were successfully implanted with VX2 cells, leading to a grossly apparent spinal and paraspinal tissue mass. The CTF guidance provided accurate placement of the acoustic ablator in all tumors, as corroborated through gross and microscopic histology. Significant tumor death was noted in all specimens without collateral damage to nearby nerve tissue. Tissue destruction just beyond the margin of the tumor was noted in some but not all specimens. No neurological deficits occurred in response to ablation. Reconstruction of measured temperature data allowed accurate assessment of volumetric dose delivered to tissues.

Conclusions

Using a rabbit intravertebral tumor model, the authors have successfully delivered tumoricidal doses of acoustic energy via a therapeutic ultrasound ablation probe placed percutaneously with CTF guidance. The authors have thus established the first technical and preclinical feasibility study of controlled ultrasound ablation of spinal tumors in vivo.

Thermal ablation of spinal osteoid osteomas close to neural elements: technical considerations

OBJECTIVE

The purpose of this study was to evaluate experience with and determine the efficacy and safety of thermal ablation in the management of spinal osteoid osteomas close to neural elements.

MATERIALS AND METHODS

The records of all patients with osteoid osteomas of the spine managed with thermal ablation at two academic centers from 1993 to 2008 were reviewed.

RESULTS

Seventeen patients (13 male patients, four female patients; mean age, 25.9 years) had lesions in the lumbar (seven patients), thoracic (six patients), cervical (three patients), and sacral (one patient) regions of the spine. Two lesions were in the vertebral body, one was within the dens, and the others were in the posterior elements. The mean lesion diameter was 8.8 mm, and the mean distance between the lesion and the closest neural element was 4.3 mm. The lesions were managed with laser (13 lesions) or radiofrequency (four lesions) ablation. Special thermal protection techniques involving the epidural injection of gas or cooled fluid were used. Pain levels were assessed immediately before the procedure and on the day after the procedure. Long-term follow-up findings were available for 11 patients. No complications were encountered, and all patients reported relief of pain. The 11 patients who participated in long-term follow-up reported continued relief of pain.

CONCLUSION

Percutaneous thermal ablation can be used to manage spinal osteoid osteomas close to the neural elements. Special thermal protection techniques may add a margin of safety.

Pain and swelling after radiofrequency treatment of proximal phalanx osteoid osteoma: case report

Bony tumors in the hand and wrist are uncommon conditions. The objective of this article was to describe an impressive soft-tissue reaction with pain after radiofrequency ablation was used to treat a proximal phalangeal osteoid osteoma in the hand. We feel radiofrequency ablation should be cautiously used in the treatment of these lesions out of concern for similar complications.

Percutaneous radiofrequency ablation of painful osseous metastases: a multicenter American College of Radiology Imaging Network trial

BACKGROUND

The study was conducted to determine whether radiofrequency ablation (RFA) can safely reduce pain from osseous metastatic disease.

METHODS

The single-arm prospective trial included patients with a single painful bone metastasis with unremitting pain with a score >50 on a pain scale of 0-100. Percutaneous computed tomography-guided RFA of the bone metastasis to temperatures >60 degrees C was performed. Endpoints were the toxicity and pain effects of RFA before and at 2 weeks, 1 month, and 3 months after RFA.

RESULTS

Fifty-five patients completed RFA. Grade 3 toxicities occurred in 3 of 55 (5%) patients. RFA reduced pain at 1 and 3 months for all pain assessment measures. The average increase in pain relief from pre-RFA to 1-month follow-up is 26.3 (95% confidence interval [CI], 17.7-34.9; P < .0001), and the increase from pre-RFA to 3-month follow-up is 16.38 (95% CI, 3.4-29.4; P = .02). The average decrease in pain intensity from pre-RFA to 1-month follow-up was 26.9 (P < .0001) and 14.2 for 3-month follow-up (P = .02). The odds of lower pain severity at 1-month follow-up were 14.0 (95% CI, 2.3-25.7; P < .0001) times higher than at pre-RFA, and the odds at 3-month follow-up were 8.0 (95% CI, 0.9-15.2; P < .001) times higher than at pre-RFA. The average increase in mood from pre-RFA to 1-month follow-up was 19.9 (P < .0001) and 14.9 to 3-month follow-up (P = .005).

CONCLUSIONS

This cooperative group trial strongly suggests that RFA can safely palliate pain from bone metastases.

The use of radiofrequency ablation in the treatment of musculoskeletal tumors

Musculoskeletal tumors, both primary neoplasms and metastatic lesions, present a therapeutic challenge for the physician who wishes to provide palliative pain relief using the least invasive approach. The increasing sophistication of imaging modalities such as CT in precisely localizing neoplasm, coupled with the widespread use of radiofrequency ablation (RFA) for treatment of other types of tumor, has generated interest in using RFA to treat musculoskeletal tumors. Primary bone tumors (eg, osteoid osteoma) and metastatic bone tumors have been successfully treated with RFA. Success rates with RFA are equal to those with standard surgical curettage, but RFA has the advantage of decreased surgical morbidity. The procedure is relatively safe, is well-tolerated by the patient, and typically can be performed on an outpatient basis. The most common serious complication reported is localized skin necrosis, which occurs rarely. RFA appears to be a viable minimally invasive approach for palliative treatment of selected bone tumors.

Treatment of pathologic spinal fractures with combined radiofrequency ablation and balloon kyphoplasty

Background

In oncologic patients with metastatic spinal disease, the ideal treatment should be well tolerated, relieve the pain, and preserve or restore the neurological function.

The combination of fluoroscopic guided radiofrequency ablation (RFA) and kyphoplasty may fulfill these criteria.

Methods

We describe three pathological vertebral fractures treated with a combination of fluoroscopic guided RFA and kyphoplasty in one session: a 62-year-old man suffering from a painful L4 pathological fracture due to a plasmocytoma, a 68-year-old man with a T12 pathological fracture from metastatic hepatocellular carcinoma, and a 71-year-old man with a Th12 and L1 pathological fracture from multiple myeloma.

Results

The choice of patients was carried out according to the classification of Tomita. Visual analog score (VAS) and Oswestry disability index (ODI) were used for the evaluation of the functional outcomes. The treatment was successful in all patients and no complications were reported. The mean follow-up was 6 months. Marked pain relief and functional restoration was observed.

Conclusion

In our experience the treatment of pathologic spinal fractures with combined radiofrequency ablation and balloon kyphoplasty is safe and effective for immediate pain relief in painful spinal lesions in neurologically intact patients.

Percutaneous thermal ablation in the head and neck: current role and future applications

Patients with recurrent head and neck cancer have poor quality of life and suffer dismally from debilitating symptoms. Ablative techniques offer patients an alternative, minimally invasive treatment option. As a palliative treatment, they improve quality of life with decreased pain, improved function and appearance. In addition, there is a reduction in tumor bulk and analgesia requirements. Advantages include a reduction in procedural cost, avoidance of complex repetitive surgeries, and an ability to visualize the treated area at the time of the procedure. Ablation therapies are an evolving and exciting treatment option in the head and neck, but a consensus on appropriate indications is currently unclear.

Combined cementoplasty and radiofrequency ablation in the treatment of painful neoplastic lesions of bone

PURPOSE

To assess the safety and effectiveness of combined radiofrequency (RF) ablation and cementoplasty in the treatment of painful neoplastic lesions of bone.

MATERIALS AND METHODS

The authors performed a retrospective analysis of 25 combined treatments comprising RF ablation followed by injection of polymethylmethacrylate cement performed in 19 patients during a 22-month period. Patients ranged in age from 42 to 82 years (mean, 58.9 years) and included five women and 14 men. Eleven vertebrae (eight lumbar and three thoracic), nine acetabulae, three sacra, one pubis, and one humerus were treated with a total of 36 RF ablations (in several instances, overlapping ablations were used). The location of the primary neoplasm, lesion size, pain before and after the procedure (as determined with a 10-point visual analog scale [VAS]), number of RF treatments, type of device used for cementoplasty, RF time, cement volume, and extravasation were documented.

RESULTS

A total of 25 combined RF ablations and cementoplasties were performed. The technical success rate was 100% (25 of 25 treatments). There were seven minor complications: six limited cement extravasations and a transient thermal nerve injury. The mean RF time was 9.1 minutes (range, 6-12 minutes). The mean cement volume injected was 6.1 mL (range, 0.8-16 mL). The mean preprocedure pain (as measured with a VAS) was 7.9 (range, 7.0-9.0) and the mean posttreatment pain was 4.2 (range, 0-6); the difference was statistically significant (mean score, 4.08; 95% confidence interval: 3.92, 4.87; P < .0001) using a paired t test.

CONCLUSIONS

Combined RF ablation and cementoplasty appears to be safe and effective in the treatment of painful neoplastic lesions of bone.

Image-guided ablation therapy of bone tumors

A wide range of thermal and cryoablation methods is currently available for the curative eradication or palliative treatment of a variety of bone and soft-tissue tumors. Radiofrequency ablation has been developed as a multipurpose tool for the skeletal system. Cryoablation has the added advantages of direct computed tomography or magnetic resonance visualization and monitoring of treatment outcome with less peri- and postoperative pain. Use of appropriate thermo-sensors and insulation techniques, like carbon dioxide insufflation, results in enhanced safety and efficacy. Ablation of weight-bearing bones has to be supplemented with cement consolidation. The authors present an overview of the current status of percutaneous image-guided ablation therapy of bone and soft-tissue tumors, analyze the merits and limitations of the various systems available, and discuss possible new applications for the future.

Radiofrequency ablation of spinal osteoid osteoma: clinical outcome

STUDY DESIGN

A prospective study on 24 patients with spinal osteoid osteoma treated with radiofrequency ablation (RFA).

OBJECTIVE

To determine if and when computed tomography (CT)-guided RFA is a safe and effective treatment for spinal osteoid osteomas.

SUMMARY OF BACKGROUND DATA

Surgery has been considered the standard treatment for spinal osteoid osteomas. Surgery may cause spinal instability, infection, and nervous injury. We evaluated CT-guided RFA as an alternative treatment.

METHODS

A total of 28 RFA procedures in 24 patients with spinal osteoid osteoma were performed, using a 5-mm noncooled electrode. Clinical symptoms and spinal deformity were evaluated before and after the procedure. Unsuccessful treatment was defined as the presence of residual or recurrent symptoms. The mean follow-up was 72 months (range: 9-142 months).

RESULTS

Nineteen (79%) patients were successfully treated after 1 RFA, and all except one after repeat RFA. One patient with nerve root compression needed further surgery. No complications were observed. Spinal deformity persisted in 3 of 7 patients after successful RFA.

CONCLUSION

CT-guided RFA is a safe and effective treatment for spinal osteoid osteoma. Surgery should be reserved for lesions causing nerve root compression.

Thermal protection during percutaneous thermal ablation procedures: interest of carbon dioxide dissection and temperature monitoring

Percutaneous image-guided thermal ablation of tumor is widely used, and thermal injury to collateral structures is a known complication of this technique. To avoid thermal damage to surrounding structures, several protection techniques have been reported. We report the use of a simple and effective protective technique combining carbon dioxide dissection and thermocouple: CO(2) displaces the nontarget structures, and its low thermal conductivity provides excellent insulation; insertion of a thermocouple in contact with vulnerable structures achieves continuous thermal monitoring. We performed percutaneous thermal ablation of 37 tumors in 35 patients (4 laser, 10 radiofrequency, and 23 cryoablations) with protection of adjacent vulnerable structures by using CO(2) dissection combined with continuous thermal monitoring with thermocouple. Tumor locations were various (19 intra-abdominal tumors including 4 livers and 9 kidneys, 18 musculoskeletal tumors including 11 spinal tumors). CO(2) volume ranged from 10 ml (epidural space) to 1500 ml (abdominal). Repeated insufflations were performed if necessary, depending on the information given by the thermocouple and imaging control. Dissection with optimal thermal protection was achieved in all cases except two patients where adherences (one postoperative, one arachnoiditis) blocked proper gaseous distribution. No complication referred to this technique was noted. This safe, cost-effective, and simple method increases the safety and the success rate of percutaneous thermal ablation procedures. It also offers the potential to increase the number of tumors that can be treated via a percutaneous approach.

Computer modeling of the combined effects of perfusion, electrical conductivity, and thermal conductivity on tissue heating patterns in radiofrequency tumor ablation

PURPOSE

To use an established computer simulation model of radiofrequency (RF) ablation to characterize the combined effects of varying perfusion, and electrical and thermal conductivity on RF heating.

METHODS

Two-compartment computer simulation of RF heating using 2-D and 3-D finite element analysis (ETherm) was performed in three phases (n = 88 matrices, 144 data points each). In each phase, RF application was systematically modeled on a clinically relevant template of application parameters (i.e., varying tumor and surrounding tissue perfusion: 0-5 kg/m(3)-s) for internally cooled 3 cm single and 2.5 cm cluster electrodes for tumor diameters ranging from 2-5 cm, and RF application times (6-20 min). In the first phase, outer thermal conductivity was changed to reflect three common clinical scenarios: soft tissue, fat, and ascites (0.5, 0.23, and 0.7 W/m- degrees C, respectively). In the second phase, electrical conductivity was changed to reflect different tumor electrical conductivities (0.5 and 4.0 S/m, representing soft tissue and adjuvant saline injection, respectively) and background electrical conductivity representing soft tissue, lung, and kidney (0.5, 0.1, and 3.3 S/m, respectively). In the third phase, the best and worst combinations of electrical and thermal conductivity characteristics were modeled in combination. Tissue heating patterns and the time required to heat the entire tumor +/-a 5 mm margin to >50 degrees C were assessed.

RESULTS

Increasing background tissue thermal conductivity increases the time required to achieve a 50 degrees C isotherm for all tumor sizes and electrode types, but enabled ablation of a given tumor size at higher tissue perfusions. An inner thermal conductivity equivalent to soft tissue (0.5 W/m- degrees C) surrounded by fat (0.23 W/m- degrees C) permitted the greatest degree of tumor heating in the shortest time, while soft tissue surrounded by ascites (0.7 W/m- degrees C) took longer to achieve the 50 degrees C isotherm, and complete ablation could not be achieved at higher inner/outer perfusions (>4 kg/m(3)-s). For varied electrical conductivities in the setting of varied perfusion, greatest RF heating occurred for inner electrical conductivities simulating injection of saline around the electrode with an outer electrical conductivity of soft tissue, and the least amount of heating occurring while simulating renal cell carcinoma in normal kidney. Characterization of these scenarios demonstrated the role of electrical and thermal conductivity interactions, with the greatest differences in effect seen in the 3-4 cm tumor range, as almost all 2 cm tumors and almost no 5 cm tumors could be treated.

CONCLUSION

Optimal combinations of thermal and electrical conductivity can partially negate the effect of perfusion. For clinically relevant tumor sizes, thermal and electrical conductivity impact which tumors can be successfully ablated even in the setting of almost non-existent perfusion.

Treatment of bone tumours by radiofrequency thermal ablation

Radiofrequency thermal ablation (RFTA) is considered the treatment of choice for osteoid osteomas, in which it has long been safely used. Other benign conditions (chondroblastoma, osteoblastoma, giant cell tumour, etc.) can also be treated by this technique, which is less invasive than traditional surgical procedures. RFTA ablation is also an option for the palliation of localized, painful osteolytic metastatic and myeloma lesions. The reduction in pain improves the quality of life of patients with cancer, who often have multiple morbidities and a limited life expectancy. In some cases, these patients are treated with RFTA because conventional therapies (surgery, radiotherapy, chemotherapy, etc.) have been exhausted. In other cases, it is combined with conventional therapies or other percutaneous treatments, e.g., cementoplasty, offering faster pain relief and bone strengthening. A multidisciplinary approach to the management of these patients is recommended to select the optimal treatment, including orthopaedic surgeons, neurosurgeons, medical and radiation oncologists and interventional radiologists.

Minimally invasive management of spinal metastases

In most patients who have spinal metastases, treatment is mainly palliative. The conventional surgical methods carry higher risks of complications and postoperative morbidity. Minimally invasive spinal interventions seem to be reasonable alternatives to treat spinal metastatic disease. These procedures can result in less soft tissue trauma, lower blood loss, shorter hospitalization time and are better tolerated by the patients. In this review, the techniques and results of minimally invasive management in spinal metastasis, including percutaneous image-guided interventions (vertebroplasty, kyphoplasty, and radiofrequency ablation) and minimally invasive surgical techniques (endoscopic and minimal access operations), are presented.

Percutaneous core excision and radiofrequency thermo-coagulation for the ablation of osteoid osteoma of the spine

Percutaneous radiofrequency ablation is the treatment of choice for osteoid osteoma of the appendicular skeleton. However, difficulties in localizing the lesion in the spine and its proximity to neural elements have yet to make it the prevalent treatment for spine. This study assesses the safety and effectiveness of two percutaneous techniques for ablating osteoid osteoma of the spine. Seven patients were treated between 1998 and 2005. Four patients underwent percutaneous radiofrequency coagulation. The lesions were located at the articular processes of L3 and L4, the lamina of L3 and in the head of the 11th rib. Three patients with lesions in close proximity to neural structures (pedicle of T9, the posterolateral inferior aspect of L3 vertebral body and the inferior articular process of C5) were subjected to percutaneous core excision. Mean follow-up was 4.2 +/- 1.6 years. Three out of four patients who underwent radiofrequency ablation had an immediate and sustained response. One patient with a lesion in the head of the rib failed to respond. The three patients in the group of pecutaneous core excisional biopsy demonstrated immediate relief of pain. However, one patient experienced relapse of symptoms 6 months after transpedicular core excision. CT scan suggested partial targeting of the lesion that corroborated with histologic examination revealing only reactive tissue. Subsequent percutaneous core excision was successful. Therefore, the overall success rate was 85.7%. Mean VAS improved dramatically from 9 +/- 1 to 2 +/- 1 after surgery (P < 0.05). No neurological or other complications were encountered. This study indicates that radiofrequency ablation of spinal osteoid osteomas is safe and reasonably effective when an intact cortical shell separates the nidus from the neural elements. Percutaneous core excision can obviate the risk of thermal damage for lesions located in close proximity to the neural elements. Effectiveness of treatment can also be evaluated by CT scan and histological examination. Difficulties in targeting the nidus can lead to treatment failure. The minimal morbidity and the effectiveness of these minimally invasive procedures make them a valid alternative in the treatment of spinal osteoid osteoma.

Osteoid osteoma: diagnosis and treatment

Treatment of small but painful osteoid osteomas was traditionally based on either prolonged medication or resection. In the era of rapidly evolving minimally invasive techniques, reluctance has been posed against surgical interventions mostly due to their relatively high rates of recurrence, complications, or persistent pain. Nonetheless, incomplete pain control and intolerance to anti-inflammatory drugs unfavorably affect prognosis. The objective of this article is to explore the nature and clinical presentation of osteoid osteomas, discuss their imaging and histological features, review available data regarding surgical and percutaneous methods for addressing these lesions and comment on their feasibility, safety, and efficacy.

Heat distribution in the spinal canal during radiofrequency ablation for vertebral lesions: study in swine

PURPOSE

To prospectively evaluate the safety of radiofrequency (RF) ablation for vertebral lesions by monitoring the temperature in swine vertebral models with and without a cortical bone defect.

MATERIALS AND METHODS

The institutional animal care and use committee approved the animal studies. In vivo and ex vivo studies were performed. In the in vivo study, 20 lumbar vertebrae from six swine were locally heated by using 1- or 2-cm active-tip internally cooled electrodes. In the ex vivo study, 12 fresh pig cadaver lumbar vertebrae were extracted from four swine, and spinal tumor models with or without cortical bone defect were created by stuffing a cavity with muscle tissue and locally heated by using a 1-cm active-tip internally cooled electrode. The temperature was monitored in the spinal canal and around the vertebral body during ablation. Mann-Whitney U test was used to indicate a significant difference between groups by using 1- and 2-cm active tip in the in vivo study and between groups with and without cortical defect in the ex vivo study.

RESULTS

In the in vivo study in which 1- and 2-cm active-tip needles were used, the temperature in the spinal canal rose to 38.2 degrees C +/- 2.7 (standard deviation) and 45.5 degrees C +/- 6.2, respectively. The latter was significantly higher than the former (P < .001). In the ex vivo study in which tumor models with or without a cortical bone defect were used, the temperature in the spinal canal rose to 48.4 degrees C +/- 6.2 and 31.3 degrees C +/- 3.4, respectively. The former was significantly higher than the latter (P < .001).

CONCLUSION

For in vivo cases with a 2-cm active tip and ex vivo cases with a vertebral posterior bone defect, the temperature rose to over 45 degrees C, potentially injuring the spinal cord and peripheral nerves.

Osteoid osteoma of the spine: CT-guided monopolar radiofrequency ablation

CT-guided percutaneous radiofrequency ablation and laser photocoagulation have become the methods of choice for the treatment of all osteoid osteomas except those in contact with neural structures. We report 10 patients with spinal osteoid osteoma adjacent to the neural elements treated with 12 sessions of CT-guided monopolar radiofrequency ablation. The size range of the lesion was 3-14 mm (mean, 7.5 mm) and the distance between the nidus and the adjacent spinal cord or nerve root was 2-12 mm (mean, 5 mm). No intact cortex between the tumor and the spinal cord or nerve roots constituted an exclusion criterion because of a higher risk of undesirable neurotoxic effects. Patients were under general anesthesia. After location of the lesion, a 11G-bone biopsy was introduced into the nidus. The radiofrequency electrode was inserted through the biopsy needle and heated at 90 degrees C for 4 min. Primary success was obtained in eight patients. At follow-up (mean, 19.5 months; range, 6-24 months), pain persisted in two patients after 2 months. Both of them were re-treated. All patients are currently pain-free and complications were not detected. In our opinion, radiofrequency ablation can also be considered the treatment of choice for spinal osteoid osteoma.

Percutaneous radiofrequency ablation: relationship between different probe types and procedure time on length and extent of osteonecrosis in dog long bones

PURPOSE

We have been using radiofrequency ablation for the percutaneous treatment of osteoid osteoma since 2001. Frequently, lesions are located near the joint surface, involve the vertebral body or are close to major nerves. We seek to determine whether radiofrequency ablation (RFA) can be used safely in these cases.

MATERIALS AND METHODS

A total of 65 lesions were induced in 4 dogs. Each dog underwent RFA on the diaphysis of long bones, as well as femoral and humeral heads. Four different sessions were carried out by using 1- and 2-cm probes with or without a cool-tip system and by varying the timing of the procedure. Plain film, CT, and MRI were obtained. All bone samples were examined histologically.

RESULTS

The dogs' activity after the procedure was normal. No pathologic fractures occurred despite unrestricted activity of the animals. Cortical bone was always respected; therefore, articular cartilage has not been damaged. Radiological findings were characteristic. There were no significant differences in lesion size, probe type, and the duration of the procedure. The mean lesion diameter perpendicular to the electrode was 18.5 mm.

CONCLUSIONS

Our study confirms the insulative effect of cortical bone. RFA can be safely performed close to the joint surface without damaging the cartilage.

Image-guided radiofrequency ablation (RFA) of spinal tumors

PURPOSE

To evaluate retrospectively the efficacy and safety of radiofrequency ablation (RFA) in patients with spinal tumors.

MATERIALS AND METHODS

Forty-one patients (25 men, 16 women; age range, 46-82 years) with nonresectable primary or secondary tumor involvement of the spine unresponsive to chemo- and radiotherapy received RFA treatment. Two radiofrequency ablation systems, one with a cool-tip electrode and one with an expandable electrode catheter, were used. Both systems work impedance controlled with a power output of 150- 200 W. Each coagulation cycle lasted 12-15 min depending on tumor impedance. Several single RFA cycles of 15 min each were used for overlapping RFAs in tumors with diameters of more than 3 cm. Temperature was kept between 50 degrees C and 120 degrees C and was chosen according to spinal cord distance and patient heat tolerance during the ablation. Multi-slice computed tomography (CT) combined with C-arm fluoroscopy guided the intervention. Efficacy outcomes were assessed after about 6 weeks, 6 months, and more than 6 months using standardized questionnaires and indices regarding tumor pain, pain disability, functional activities, quality of life, neurological status, and tumor progression.

RESULTS

RFA significantly reduced tumor-induced pain within 6 weeks, improved daily activities, and maintained quality of life. Mean time to tumor progression was 730+/-54 days (Kaplan-Meier estimate). No RFA-associated complications were reported.

CONCLUSION

RFA of primary and secondary spinal tumors, which were unresponsive to chemo- and radiotherapy and prone to progression, is a safe, resource-saving, and highly effective percutaneous technique in patients with nonresectable spinal tumors.

Combined treatment of ablative therapy with percutaneous radiofrequency and cementoplasty of a symptomatic metastatic lesion of the acetabulum

We report the case of a symptomatic metastatic lesion of the acetabulum from colon adenocarcinoma in an 82-year-old woman patient treated by a combined approach of thermal ablation with percutaneous radiofrequency and cementoplasty. We obtained an immediate technical success with a good control of pain without any complications at a 6-month clinical follow-up.

Radiofrequency ablation of osseous metastases for the palliation of pain

A number of different methods have been proposed for pain relief in cancer patients with bone metastases, each with different indications, contraindications and complications (systemic analgesics, bisphosphonates, antitumor chemotherapy, radiotherapy, systemic radio-isotopes, local surgery and vertebroplasty). The ideal treatment has to be fast, safe, effective and tolerable for the patient. CT-guided radiofrequency (RF) ablation may fulfill these criteria. Our experience in the treatment of 30 patients (34 lesions) with painful bone metastases using RF ablation was assessed. There was a significant decrease in the mean past-24-h Brief Pain Inventory (BPI) score for worst pain, for average pain and for pain interference during daily life (4.7, 4.8 and 5.3 units respectively) 4 and 8 weeks after treatment. There was a marked decrease (3 out of 30 patients 4 and 8 weeks after treatment) in the use of analgesics. CT-guided RF ablation appears to be effective for treatment of painful bone metastases.

The role and limitations of radiofrequency ablation in treatment of bone and soft tissue tumors

Percutaneous radiofrequency ablation (RFA) has evolved as an alternative therapy for treatment of certain patients with liver tumors. This novel image-guided intervention is a minimally invasive form of therapy with negligible morbidity. RFA has also been used for treatment of selected patients with renal and lung malignancies who may not be suitable surgical candidates. With the exception of osteoid osteomas, surgical management remains the treatment of choice for primary bone and soft tissue tumors. The role of RFA in definitive treatment of sarcomas has not been investigated. However, RFA has replaced surgery for treatment of osteoid osteomas and can play a role in palliation of painful bone and soft tissue tumors.

The healing pattern of osteoid osteomas on computed tomography and magnetic resonance imaging after thermocoagulation

OBJECTIVE

To compare the healing pattern of osteoid osteomas on computed tomography (CT) and magnetic resonance imaging (MRI) after successful and unsuccessful thermocoagulation.

MATERIALS AND METHODS

Eighty-six patients were examined by CT and 18 patients by dynamic gadolinium-enhanced MRI before and after thermocoagulation for osteoid osteoma. Thermocoagulation was successful in 73% (63/86) and unsuccessful in 27% (23/86) of patients followed by CT. Thermocoagulation was successful in 72% (13/18) of patients followed by MRI. After treatment, the healing of the nidus on CT was evaluated using different healing patterns (complete ossification, minimal nidus rest, decreased size, unchanged size or thermonecrosis). On MRI the presence of reactive changes (joint effusion, "oedema-like" changes of bone marrow and soft tissue oedema) and the delay time (between arterial and nidus enhancement) were assessed and compared before and after thermocoagulation.

RESULTS

Complete ossification or a minimal nidus rest was observed on CT in 58% (16/28) of treatment successes (with > 12 months follow-up), but not in treatment failures. "Oedema-like" changes of bone marrow and/or soft tissue oedema were seen on MR in all patients before thermocoagulation and in all treatment failures. However, residual "oedema-like" changes of bone marrow were also found in 69% (9/13) of treatment successes. An increased delay time was observed in 62% (8/13) of treatment successes and in 1/5 of treatment failures.

CONCLUSION

Complete, or almost complete, ossification of the treated nidus on CT correlated with successful treatment. Absence of this ossification pattern, however, did not correlate with treatment failure. CT could not be used to identify the activity of the nidus following treatment. The value of MR parameters to assess residual activity of the nidus was limited in this study.

Computer modeling of the effect of perfusion on heating patterns in radiofrequency tumor ablation

PURPOSE

To use an established computer simulation model of radiofrequency (RF) ablation to further characterize the effect of varied perfusion on RF heating for commonly used RF durations and electrode types, and different tumor sizes.

METHODS

Computer simulation of RF heating using 2-D and 3-D finite element analysis (Etherm) was performed. Simulated RF application was systematically modeled on clinically relevant application parameters for a range of inner tumor perfusion (0-5 kg/m3-s) and outer normal surrounding tissue perfusion (0-5 kg/m3-s) for internally cooled 3-cm single and 2.5-cm cluster electrodes over a range of tumor diameters (2-5 cm), and RF application times (5-60 min; n = 4618 simulations). Tissue heating patterns and the time required to heat the entire tumor +/- a 5-mm margin to > 50 degrees C were assessed. Three-dimensional surface response contours were generated, and linear and higher order curve-fitting was performed.

RESULTS

For both electrodes, increasing overall tissue perfusion exponentially decreased the overall distance of the 50 degrees C isotherm (R2 = 0.94). Simultaneously, increasing overall perfusion exponentially decreased the time required to achieve thermal equilibrium (R2 = 0.94). Furthermore, the relative effect of inner and outer perfusion varied with increasing tumor size. For smaller tumors (2 cm diameter, 3-cm single; 2-3 cm diameter, cluster), the ability and time to achieve tumor ablation was largely determined by the outer tissue perfusion value. However, for larger tumors (4-5 cm diameter single; 5 cm diameter cluster), inner tumor perfusion had the predominant effect.

CONCLUSION

Computer modeling demonstrates that perfusion reduces both RF coagulation and the time to achieve thermal equilibrium. These results further show the importance of considering not only tumor perfusion, but also size (in addition to background tissue perfusion) when attempting to predict the effect of perfusion on RF heating and ablation times.