At the 2005 Annual Scientific Meeting of the Society of Interventional Radiology, held March 31 through April 5, 2005, in New Orleans, Patrick E. Sewell, MD, led the session on organ-specific oncologic therapy of bone. Sewell, who is assistant professor of radiology and surgery at the University of Mississippi Medical Center, Jackson, reports that approximately 100,000 cases per year of bone metastasis are reported in the United States. This makes bone the third most common site to which cancer metastasizes, with three fourths of the primary tumors that metastasize to bone arising in the breast, prostate, lung, and kidney. Metastases from the prostate tend to be sclerotic, while metastases from the breast, lung, and kidney more typically destroy bone, but both types of damage can be treated successfully. Treatment may not be curative, but pain can be eliminated and the patient’s quality of life can be greatly improved.
According to Sewell, roughly 70% of patients who have bone metastases experience pain as a result. As a metastatic tumor erodes a bone, large holes are created. This not only makes the bone thin and weak, but also makes the nerves in and surrounding the bone send pain signals to the brain. The spinal cord can be compressed as vertebral bone is destroyed; weight-bearing bones can also fracture. Both events are seriously detrimental to the patient’s mobility and overall quality of life.
Techniques of Interest
Usually, the first bones affected by metastases are the ribs, pelvis, and spine. Bone tumors in the spine can be the cause of major neurological damage. For example, paralysis can result if a tumor is pressing against the spinal cord. If permanent damage of this kind is to be avoided, early detection of bone tumors is vital. Most treatment for bone tumors will be palliative, but preventing additional bone destruction will increase the patient’s mobility and functional capabilities, in addition to reducing pain. In certain cases, bone-tumor ablation can prolong survival, even if the primary tumor is located elsewhere. Three minimally invasive techniques of widespread interest in the treatment of bone metastases are radiofrequency ablation, cryoablation, and the use of bone cement.
Patrick E. Sewell, MD, is assistant professor of radiology and surgery at the University of Mississippi Medical Center, Jackson. At the 2005 Annual Scientific Meeting of the Society of Interventional Radiology, held in New Orleans on March 31 through April 5, 2005, he presented Musculoskeletal RFA, a talk that covered practical aspects of radiofrequency ablation (RFA) for tumors of bone and adjacent tissues. RFA is indicated, Sewell states, for the treatment of bone-destroying tumors that are painful and that would create structural compromise (through fracture or compression) if allowed to progress. The primary goal of RFA is to improve the patient’s quality of life by relieving the pain caused by bone tumors. In addition, RFA can be used in preparation for orthopedic stabilization, which may be used to address functional and mobility difficulties caused by bone metastases.
RFA offers the bone-tumor patient several advantages. Its effectiveness is not limited by the type of tumor cell involved, and it is, of course, minimally invasive. Pain relief following RFA is both immediate and sustained, and the procedure gives reliable, reproducible results. The therapeutic range of RFA is quite broad, and it is a relatively inexpensive treatment.
Candidates for RFA are those who have benign tumors, such as osteoid osteoma, or metastases from malignant tumors of the lung, colon, breast, kidney, or other site. No tumor-cell types are poor candidates for RFA, Sewell reports, but he adds capillary-level embolization to the treatment of patients with metastatic renal-cell carcinoma because these tumors are hypervascular.
Fluoroscopy, ultrasound, CT, and MRI can all be used for RFA imaging because the bones are near the body’s surface. RFA treatment time is usually 12 to 40 minutes. Sewell performs the procedure on an outpatient basis, unless significant comorbidity makes this undesirable. He orders standard preoperative laboratory testing, but uses preoperative antibiotics only if diabetes, recent chemotherapy, or a similar condition has compromised the patient’s immunity. He recommends listing skin burns as the most frequently noted complication of RFA when obtaining the patient’s informed consent. Sewell employs a combination of local anesthesia and conscious sedation, along with occasional monitored anesthesia care.
While skin burns are the most common complication of RFA, Sewell also characterizes them as inexcusable because they are the most avoidable complication. Burns can be caused when metal objects on the skin (such as hemostats) become heated because they absorb RF energy; burns can occur under grounding pads, above superficial targets, and at the probe’s entry site, as well. Sewell suggests using an incision at the probe-entry site that is large enough to permit the skin to be retracted away from the probe shaft so that the skin will not be burned. Wrapping the probe shaft with gauze and applying sterile, chilled water can also protect the probe-entry site from burns.
Although it is far less common than skin burning, neuropathy is the most serious complication of RFA. Sewell emphasizes the importance of avoiding the neurovascular bundle and of using the highest-quality imaging available for preoperative planning and intraoperative guidance.
Single-needle, umbrella-array, and coaxial-system probe technologies are available for RFA. Sewell prefers the umbrella array when ablating bone-destructive tumors, since these have a large interface with the periosteum that, along with soft-tissue involvement, can make it difficult to localize the cause of pain precisely. A single-needle probe is more appropriately used for small tumors or for those that can be reached only after crossing normal bone. As an alternative in such cases, the sheath from a coaxial system can be used to traverse the normal bone; once the target has been reached, partial deployment of an umbrella array can proceed.
Following RFA, Sewell does not give his patients antibiotics unless a documented infection is present. For the control of procedure-related pain (which typically lasts 1 to 3 days), he reports that nonsteroidal anti-inflammatory drugs available without prescription are adequate in all but 10% of his cases. For those, class III or class IV narcotics may be required. For 1 to 7 days following RFA, immune-stimulation fever may also be present.
|Figure 1. Pre RFA bone scan (a) demonstrates (dark area in blue oval) bone destruction from cortical destruction by the renal cell carcinoma metastasis 1 week prior to percutaneous radiofrequency ablation (RFA). Bone scan (b) obtained 6weeks after RFA procedure demonstrates a small amount of increased bone remodeling activity (slightly darker area of tumor location inside blue circle) consistent with bone healing rather than destruction. Bone scan (c) obtained 8 months after RFA procedure demonstrates continued slight increase in bone remodeling (blue oval) consistent with healing but no evidence of hypermetabolic changes seen with tumor residual or recurrence. This patient continued to be pain free since the RFA procedure and the bone destruction was halted at the time of RFA so that he remained ambulatory with no further bone loss or weakening of this bone. Images courtesy of Patrick E. Sewell, MD.|
Sewell stated that it is essential for the patient, family, and referring physician to understand what to expect of RFA. It is possible, in the presence of multiple metastases, for the source of pain to be unclear; the patient’s pain may also be unrelated to the lesion treated and, therefore, may remain unrelieved. Both spoken and written explanations of possible complications and potential risks of RFA (as well as probable benefits) should be given to patients and their families. RFA should be referred to as surgery in the presence of patients, since they are typically more willing to accept complications after an intervention called surgery than after one called a procedure. Despite the safety of RFA, risks and complications must not be glossed over without complete explanations.
If complications requiring an inpatient stay arise, Sewell recommends meeting with the patient and family daily. If burns are present, a plastic surgeon should be consulted; for neurological injury, rehabilitation should be pursued. Both steps should be taken as soon as possible.
RFA permits the interventional radiologist to provide sustained pain relief and improved quality of life to patients with bone tumors. The procedure is quickly performed at a relatively low cost, morbidity is also low, and results are highly reliable.
|Patrick E. Sewell, MD|
Musculoskeletal Cryoablation was presented in New Orleans at the 2005 Annual Scientific Meeting of the Society of Interventional Radiology (held March 31 through April 5, 2005) by Patrick E. Sewell, MD, assistant professor of radiology and surgery at the University of Mississippi Medical Center, Jackson. Cryoablation, Sewell states, is performed for local tumor control and for pain relief. The tumors most often treated using this method are found in the iliac spine, posterior element, sternum, rib, clavicle, sacrum, scapula, vertebral body, and the long bones of the extremities. The tumors most commonly treated using cryoablation, according to Sewell, are metastatic breast and colon cancer, renal-cell carcinoma, nonsmall-cell lung cancer, osteoid osteoma, sarcoma, and carcinoid tumor.
In cryoablation, tissue is frozen by an ice ball that forms as gases (such as helium and argon) under high pressure exit the tip of the probe. The resulting pressure drop creates a massive temperature decrease. Cryoablation’s natural imaging partner is MRI because a signal void is visible wherever there is frozen water. Tissue that is frozen shows as a black ice ball, so the progress of thermal ablation can be monitored and guided visually using MRI.
Before cryoablation, preoperative laboratory work should include a complete blood count and a determination of coagulation parameters. Antibiotics, in the absence of skin injury, are not used prophylactically.
During the procedure, the patient can be given local anesthesia, conscious sedation, or general anesthesia, as needed. Sewell uses a probe insulation sheath, as well as warm saline gauze at the probe-entry site, to prevent unwanted surface freezing. He applies a tissue sealant and a skin-bonding agent to the site, as well.
Although complications of cryoablation are uncommon, they can include neuropathy and dermal injury. Cryoablation, however, is unique in that is does not increase the patient’s risk of future neuronal tumor. If skin injury occurs, infection and osteomyelitis become more likely to follow, so antibiotic agents should be used. Any neuropathy that arises after cryoablation will probably be transient, reversing itself within 1 to 2 month because axonal regeneration (at a rate of 0.3 mm per day) proceeds along the intact myelin sheath.
Cryoablation of bone tumors is generally an outpatient procedure. Intraprocedural MRI provides the highest degree of precision, permitting ablation of the tumor without damage to healthy tissue surrounding it. This increased accuracy reduces complication rates, Sewell reports. MRI guidance and monitoring also make it possible to treat tumors in locations so difficult to reach that they would otherwise be considered untreatable. For example, spinal metastases of renal-cell carcinoma, which are destructive and painful, cannot be treated using other methods due to excess mortality. Cryoablation, however, produces sustained pain reduction (or elimination) for patients with this condition and other types of bone tumors.
BONE CEMENT FOR VERTEBRAL COMPRESSION FRACTURES
|Judson E. Threlkeld, MD|
Judson E. Threlkeld, MD, is interventional section chief and catheterization laboratory director, department of radiology, Southwest Washington Medical Center, Vancouver, Wash. At the 2005 Annual Scientific Meeting of the Society of Interventional Radiology, held in New Orleans on March 31 through April 5, 2005, he presented Cement for Bone Tumors: Minimally Invasive Treatment of Tumor-related Fractures. Kyphoplasty or vertebroplasty using bone cement can be used to treat primary bone tumors, metastatic bone disease, and multiple myeloma. Both procedures use methylmethacrylate (bone cement) to fill spaces in bone; kyphoplasty employs a balloon to create a hollow area that is then filled with a thick bone cement injected under low pressure, while vertebroplasty uses high-pressure injection of thin cement without a balloon. Threlkeld states that primary bone tumors are relatively uncommon, with the United States having approximately 2,400 cases (and 1,300 deaths) attributed to primary bone tumors per year. The types of tumors that arise from bone are Ewing sarcoma, osteosarcoma, chondrosarcoma, and malignant fibrous histiocytoma. Most skeletal tumors, however, arise from primary cancer elsewhere in the body. Of the more than a half million people in the United States who die of cancer each year, 30% to 70% have bone metastases, Threlkeld says.
Metastatic bone diseases can be responsible for hypercalcemia, spinal-cord compression, fractures of the long bones and pelvis, vertebral compression fractures, and pain. The lesions themselves may be osteoblastic, osteolytic, or mixed. Primary prostate cancer often produces osteoblastic lesions, with increased bone density but decreased bone stiffness. Primary tumors of the bladder and thyroid typically create osteolytic metastases that decrease bone density, strength, and stiffness and that are more likely to result in fracture than are osteoblastic lesions. Patients with renal-cell carcinoma and multiple myeloma also exhibit osteolytic lesions, while patients with lung cancer may have bone metastases of osteolytic or mixed types. Primary breast cancer can produce metastases that are osteolytic, mixed, or osteoblastic.
The prognosis is generally poor for patients whose primary tumors have metastasized to the bones. The median time that elapses between the initial diagnosis of cancer and bone metastasis is 30 months, Threlkeld notes, but median survival after that point can be as short as 5 months for patients with lung cancer or as long as 30 to 60 months for those with multiple myeloma. Those who survive longer are naturally more likely to need treatment for the skeletal damage caused by bone metastases, which are most commonly found in the vertebrae, pelvis, femur, and hip.
MRI is the most useful imaging modality for the diagnosis of metastatic bone disease, although CT is also used. Radiography will indicate the presence of a metastasis only if it has already destroyed a large area of the bone. Blood-calcium levels can be tested as another means of diagnosis, and needle biopsy can be used for the confirmation of suspected lesions.
|Threlkeld performs kyphoplasty on patient with tumor-related vertebral compression fracture.|
In addition to reducing pain and treating fractures, the use of bone cement for metastatic bone lesions can prevent both recurrent fractures and neurological complications. Tumor-related vertebral compression fractures are one of the most rewarding areas for the application of bone cement, since the height of the vertebral body can be restored at the same time that pain is treated, thus correcting spinal deformity.
Before using bone cement to treat a vertebral compression fracture, the interventional radiologist should obtain standard preoperative laboratory work and a detailed patient history that emphasizes the severity and duration of pain and the age of the fracture. Comorbidities that could affect the choice of anesthesia type and operative position are also evaluated at this time. Vertebroplasty and kyphoplasty can be performed as inpatient or outpatient procedures, as the patient’s overall health warrants. Preoperative imaging is ideally performed using MRI, but bone scans can be useful in patients whose pacemakers or other implants are contraindications for MRI scanning.
Vertebroplasty should not be used if the patient has a spinal or systemic infection, if the vertebral body has lost more than 70% of its height, if the cortex of the vertebral body is pushed into the spinal canal to a moderate or severe degree, or if the patient has an uncorrected coagulation disorder. Threlkeld prefers kyphoplasty, where it can be used, because its complication rates appear to be lower than those for vertebroplasty. He notes that, while serious adverse events have been associated with acrylic bone cements, no complications of kyphoplasty have been reported (to date) after treatment of tumor-related vertebral compression fractures, although complications for osteoporotic vertebral compression fractures have been reported.