Spinal, 15
Brain, and Nerve Ablation
Lisa Ruehlow
Ablation is used to improve many different neurological symptoms. This chapter serves to provide an overview of some of the common techniques used in neurosurgery today. Ablative techniques and equipment used for brain tumors, Parkinson's disease, and disc degeneration are discussed, as well as a brief description of some of the treatments used for chronic pain and spasticity. Ablation is less commonly done in cases of dystonia or epilepsy, which are mentioned at the end of this chapter. Cochlear implants and scoliosis also involve the use of ablation, but will be covered in Chapter 23.
15.1 Brain tumors
A brain tumor is defined as a mass of unnecessary, abnormal cells growing in the brain. Primary brain tumors are tumors that start in the brain; they can be benign or malignant (cancerous). Both the benign and malignant brain tumors are equally dangerous due to the brain's vital importance and limited space. Secondary tumors start in other locations of the body and spread to the brain. 15.1.1 Nonablative Treatments Medication Various medications are given to people with brain tumors to control the symptoms that may occur; they do not, however, actually treat the tumor. Medications include steroids for controlling pressure, anticonvulsants for those prone to seizures, antinausea pills, anticoagulants to control blood clotting, and antidepressants (Musella Foundation, 2003). Chemotherapy is also an option for brain tumor treatment. There are several different options for chemotherapy and some of them have been shown to be very effective in reducing the size of the tumors.
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Resective Surgery Removal of the tumor tissue is often the most effective treatment. This involves opening the skull and cutting out the portion of the brain that is diseased. The problem with this procedure is that certain areas cannot be removed as they are functionally important. Radiosurgery Radiosurgery is used as a noninvasive method to treat brain tumors. A focused, high-energy dose of radiation is delivered to the precise area (e.g., tumor) using stereotactic imaging techniques. The procedure lasts approximately 30 minutes and the patient may leave the hospital on the same day. 15.1.2 Picosecond or Femtosecond Laser Ablation Laser ablation is used in the case of deep seated brain tumors where it would be difficult to do a direct resection of the tissue. Initial laser techniques, such as laserinduced interstitial thermotherapy (LITT), concentrated on laser radiation or heating of the tissue to temperatures above 60 C. The problem with this procedure is that thermal diffusion leads to damage of surrounding healthy tissue and exact ablation of tumor tissue is impossible with complicated tumor geometries. It is also limited by the necessity for temperature control and the rather small reachable volume. The picosecond or femtosecond laser ablation instead focuses on nonthermal plasma-induced ablation using a computer-guided probe to destroy the tumor (Fischer et al., 1994). Technique A block diagram of the ablation procedure is shown in Figure 15.1. Preoperative images are used to identify the target, and the trajectory is defined with respect to the location and geometry of the tumor. This trajectory is transferred to a personal computer (PC) which controls the probes movements after the probe is manually inserted into the area of interest (Sturm et al., 1983).
Section No. Title 3
Coagulating laser Beam guidance Picosecond Nd:YLF laser
Detection of plasma spark Supervising PC Laser probe Microscope Patient
CT & MR data (offline) Preoperative planning/ Image presentation
Figure 15.1 Block diagram of the tissue ablation system including the patient, laser, and PC control. Adapted from Goetz et al., 1999.
The manual insertion of the probe is done using a stereotactic head frame. This frame screws to the patient's head to help stabilize it and also to guide the instruments to the correct location. Preoperative MRI scans with the head frame generate coordinates that are later used to insert the probe. A burr hole of approximately 7 mm is created in the skull and the probe is inserted directly into the target volume. The final location of the probe is verified using X rays (Goetz et al., 1999). The probe is then guided by the computer using the previously identified geometries and is monitored using MRI or ultrasound. A confocal laser-scanning microscope within the probe is used to detect blood vessels. Coagulation of blood in the vessels is necessary before the ablation begins to prevent excessive bleeding. A microplasma spark is used to control the distance to the tissue surface (Goetz et al., 1999). Ultrashort laser pulses are used to nonthermally ablate the tumor into smaller fragments. Picosecond or femtosecond laser pulses are used because they are much shorter than the thermal relaxation time of brain tissue and cause a plasma-mediated response. The plasma is responsible for breaking up the tumor. Figure 15.2 shows the tumor fragments, which are later removed using suction (Fischer et al., 1994).
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Figure 15.2 Scanning electron microscope image of ablated tissue fragments from bovine tissue samples (Goetz et al., 1999).
Equipment A schematic drawing of the probe is illustrated in Figure 15.3. It is comprised of three coaxial tubes that fix the probe's location within the brain, and a mirror and lens to allow for laser focusing. The space between the tubes is used for irrigation and suction to simultaneously remove tissue fragments during ablation. The combined rotational and lateral movement of the laser results in a cylindrical geometry of ablated tissue with a maximum height of 40 mm and diameter of 50 mm. Figure 15.2(c) illustrates this geometry.
Optical Channel
40 mm
Movable focusing lens (f = 45 mm)
2.8 mm 4.0 mm 5.1 mm Ablation geometry
rotation (a) (b) (c)
Figure 15.3 (a) Schematic drawing of a probe showing the three cylindrical chambers and the mirror and lens used to focus the laser. (b) Cross section showing the irrigation and suction channels. (c) Shape of the tumor ablation. Adapted from Goetz et al., 1999.
Section No. Title 5
The system also contains a pressure control system that produces a steady stream of sodium chloride solution to clean and cool the instrument surface. Intracranial pressure (ICP) is monitored and if it gets too high, the flow rate of the cleaning solution is lowered. The maximum allowable ICP is 20 mmHg. Probe specifications are listed in Table 15.1 (Wahrburg and Schmidt, 1996).
Table 15.1 Probe specifications for picosecond or femtosecond laser ablation techniques (Wahrburg and Schmidt, 1996).
Specification Average power Maximum energy Maximum repetition rate Ablation velocity Pulse duration ICP limit Value 1.5 W 1.5 mJ 1 kHz 50 mm3/min 30 ps 20 mmHg
Results Although currently available laser power is able to resect small volumes, it is not sufficient to resect larger volumes within a suitable timeframe. A commercial diode-pumped 10 W laser with 2.5 mJ at a repetition rate of 4 kHz is currently being developed by Time-Bandwidth Products Inc., Switzerland. The largest risk of this technique is bleeding. Possibly by combining this technique with LITT, which could heat the entire tumor and coagulate the blood in the vessels, the risk of bleeding could be reduced (Goetz et al., 1999). 15.1.3 Radiofrequency Ablation Radiofrequency energy has been used successfully in the neurosurgical field and has shown to be safe, well-controlled and reproducible (Anzai et al., 1995). MRguided radiofrequency ablation can be used as a minimally invasive treatment of brain tumors. Technique An MR-compatible stereotactic frame is placed on the patient's head and the patient is placed in the MR scanner. The stereotactic coordinates are determined for the placement of the electrode in the brain. Local anesthesia is given to the patient at the predetermined probe entrance location. A 5 mm incision is made to allow for a small hole to be drilled into the skull. The MR-compatible RF probe is placed through the opening and impedance monitoring is done as the electrode is advanced to the tumor site. The status of the patient is monitored throughout the procedure.
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A modified MR-compatible radiofrequency generator system (Radionics, Inc.) is used to generate 480 kHz sine wave signals. The temperature is increased to 80 C and maintained for 1 min. This well accepted technique achieves results in a local area of coagulation and tissue necrosis. The one minute applications are repeated for the entire tumor area. The goal is to cover the entire volume of the tumor with lesions as well as a small portion of the normal surrounding tissue. The probe is then removed and the incision is closed using one to two nylon sutures. MR-imaging is used to monitor the lesion (Anzai et al., 1995). Equipment A radiofrequency generator is used to create the thermal energy for ablation. These generators have the capability to do impedance monitoring, stimulation, temperature monitoring, and lesion timing. The RFG-3CF by Radionics is a generator often used for radiofrequency lesioning in neurosurgery; Table 15.2 lists the specifications. The stimulation parameters listed for this RF generator are for short pulses; short pulses are used so that the brain tissue is not actually destroyed during the probe localization process when stimulation is commonly done.
Table 15.2 Specifications for the Radionics RFG-3CF neurosurgery RF generator.
Specification Electrical volts Impedance monitoring Stimulator output rate Stimulator duration Stimulator amplitude Temperature monitoring RF lesion generator timing RF voltage output RF current output RF power output RF impedance output RF temperature output Safety standards Range Domestic: 110 - 117 V AC International: 220 240 V AC 0 - 5000 one shot, 2, 5, 10, 20, 50, 75, 100, 150, 180, 200 Hz 0.1, 0.2, 0.5, 1.0 ms Voltage stimulation: 0 - 1 V or 0 - 10 V Constant current stimulation: 0 - 1 mA or 0 - 10 mA 20 - 99 C 0 120 s (selectable) 0 - 100 RF V 0 1000 RF mA 0 50 RF W 0 5000 20 100 C UL544
The typical probe used for brain tumor ablation is either a 5 or 10 mm straight-tip exposed electrode. In order to create larger lesions, a cool-tip probe has been developed. The circulation of fluid reduces the heat at the contact surface. This allows larger lesions to be made. Results
Section No. Title 7 The use of MR-guided RF ablation has been shown to be effective in the treatment of brain tumors. It is minimally invasive, accurately targets the diseased tissue, and can be visualized on MR scans immediately following the procedure. One possible limitation of the technique is lesion size. Lesion size is determined by many factors including: current intensity, temperature of tip, duration of application, size of exposed electrode, and properties of the tissue to be treated (Anzai et al., 1995). One possible solution is the use of cool-tip ablation probes which are capable of creating larger lesions.
15.2 Parkinson's Disease
Parkinson's disease is a movement disorder that results from the degeneration of dopamine-producing nerve cells in the substantia nigra nucleus (see Figure 15.4). Dopamine is a neurotransmitter that stimulates motor neurons, and its depletion results in tremors, rigidity, and bradykinesia (slow initiation of movement).
Thalamus Globus palidus
Putamen
Subthalamic nucleus
Substantia nigra
Figure 15.4 Coronal slice of the brain showing anatomical structures important to Parkinson's disease. The substantia nigra is the location of dopamine degeneration. The thalamus and globus pallidus are the typical ablation sites used to treat the symptoms of Parkinson's disease.
15.2.1 Nonablative Treatments Medication The gold standard for the treatment of Parkinson's disease is Levodopa therapy which was approved by the FDA in 1970. Levadopa is a chemical which is
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converted into dopamine in the brain, thus replacing the lost dopamine from the substantial nigra. Long-term usage of this drug can result in complications such as dyskinesia (uncontrolled writhing movements). Alternatives are being looked at to reduce exposure time to levodopa including using other drugs in combination with levodopa during different stages of the disease. Three drugs approved by the FDA in 1997 which have been very effective in reducing Levodopa exposure are: Mirapex, Requip, and Tasmar (Henkel, 1998). Deep Brain Stimulation Deep brain stimulation is used to help control tremors, rigidity, and bradykinesia in patients with Parkinson's disease. An electrode is placed into the brain through a burr hole using stereotactic techniques. It is typically placed within the subthalamic nucleus and is connected to a generator implanted in the chest. This generator provides a constant stimulus to the area of the brain which reduces the patient's movement disorders. Gamma Knife Surgery Gamma knife surgery involves creating lesions in the thalamus or globus pallidus to control movement problems. The lesions are created noninvasively using gamma rays focused on the area of interest for approximately 1 hour. The use of gamma knife surgery has been shown to have a success rate of 88.9% in controlling tremors; however, there have also been reports of significant complications (Young et al., 1998; Okun et al., 1995). 15.2.2 Radiofrequency Ablation Radiofrequency (RF) ablation is used to destroy the tissue that produces the abnormal chemical or electrical impulses producing tremors and dyskinesia in people with Parkinson's disease. These ablative procedures were commonly used prior to the FDA approval of Levadopa therapy. However, they are becoming more common again as the surgical procedures have been refined and complications of long-term Levadopa therapy have become more obvious. There are two different types of ablation that are done for Parkinson's disease. Pallidotomy is the ablation or destruction of the posteroventral region of the medial globus pallidus to eliminate uncontrolled dyskinesia. Thalamotomy is the ablation of a small section of the thalamus (central intermediate nucleus) to eliminate tremors. A related procedure is cryothalamotomy, which uses a supercooled probe inserted into the thalamus to freeze (rather than heat) and destroy areas that produce tremors (Neurology Channel, 2002). The anatomical locations of the globus pallidus and thalamus are depicted in Figure 15.4. Technique
Section No. Title 9 Similar to tumor ablation, a stereotactic head frame is used and a burr hole created. The probe is then inserted into the target area using the head frame coordinates. There is some controversy, however, over the technique used to navigate the probe to the correct location. Macrostimulation is generally used in all occurrences; however, the use of microelectrode recording is under debate. Some people feel that this enhances the efficacy and safety, while others feel that it increases the risk of complications due to multiple passes of the electrode and requires longer operating times and more operating room staff (Eskandar et al., 2000). Microelectrode recording is done via high impedance (0.5 to 1.0 M) microelectrodes with tip diameters of 2 to 4 m (Vitek et al., 1998). These electrodes are typically connected to a microdrive system. An example microdrive and recording system is the Alpha Omega MicroGuide. This system allows for recording, stimulation (0 to 10 mA), and impedance monitoring of 1 to 5 electrodes simultaneously. As the microelectrodes advance, patterns of neural activity are monitored on a computer screen and the depths from the starting position are recorded (Alpha Omega Engineering, 2003). Each cellular region has a characteristic neural pattern which allows for identification of the putamen, globus pallidus, and nucleus basalis as shown in Figure 15.5.
Figure 15.5 Microelectrode recordings of different cellular regions within the brain. These recordings allow for electrode localization during the ablation procedure (Vitek et al., 1998). After the target is selected, the recording electrode is replaced at the same position by a lesioning electrode. Macrostimulation is done before ablation to assess proximity to the optic tract, potential for speech dysfunction, and amelioration of symptoms (Eskander et al., 2000). Stimulation is applied and the patient's symptoms (i.e. rigidity and tremors) are monitored for improvement as well as screening for side effects. After stimulation, a test lesion is often made at 46 to 48 C for 60 s. If no motor, sensory, visual, or speech impairments occur, a permanent lesion is made at 70 to 80 C for 60 s (Eskander et al., 2000). The RF generator provides energy to create a thermal lesion several millimeters in diameter at the tip of the probe (Griffith, 2000).
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Equipment This procedure requires the use of a stereotactic head frame with a microdrive system for microelectrode recording and stimulation. The RF generator (Radionics, Inc.) is the same as that described previously for brain tumor ablation. However, the electrode commonly used has a smaller area with a 1.1 to 1.3 mm diameter and a 3 mm exposed tip (Gross et al., 1999; Vitek et al., 1998). Results Thalamotomy causes improvements in tremors; however, pallidotomy yields improvements in both dyskinesia and tremors and thus is more widely used. Some people undergo unilateral pallidotomy with the possibility of a second ablation later on, while others receive bilateral ablation the first time. Figure 15.6 shows an MR image obtained after a unilateral pallidotomy procedure. Unilateral pallidotomy has been shown to improve tremors, rigidity, and bradykinesia in most patients for at least three years. Benefits are seen on the contralateral (opposite) side of the body to that of the surgery (Figure 15.7). After three years, benefits begin to wane and activities of daily living continue to worsen (Griffith, 2000).
Figure 15.6 Coronal MR image showing the needle path, indicated by the arrow, and the site of the lesion within the globus pallidus during a unilateral pallidotomy procedure (Department for Clinical Neurosciences, 1998).
Section No. Title 11
Figure 15.7 Results in dyskinesia and tremor scores preoperatively and 1.5, 3, 6, 12, and 24 months after pallidotomy for both ipsilateral and contralateral sides (Eskandar et al., 2000).
The ablation procedure is not reversible and serious complications are seen in 2 to 8% of unilateral pallidotomy cases. Visual impairment, facial paresis, hemiparesis, and changes in speech, voice volume, and memory may be affected if the lesion spreads beyond the target area. Bilateral pallidotomy is associated with
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an increased risk of complications, in particular speech dysfunction, drooling, balance impairment, and memory problems (Griffith, 2000). The advantage to using ablation as a treatment of Parkinson's disease is that it is cost effective, requires no maintenance, and poses little risk of infection as compared to deep brain stimulation (DBS).
15.3 Intervertebral Disk Degeneration
Low back pain is thought to be caused by a combination of problems; however, the intervertebral disk is the primary cause in more than 50% of patients (Schwarzer et al., 1995). There are three degenerative conditions that can occur within the intervertebral disks. The first condition is a tear in the annulus fibers or the creation of a fissure. As the body ages, the annulus fibers weaken and this allows them to tear. The second condition is a herniated disk which is caused when the nucleus pulposus ruptures out through the annulus (Figure 15.8). Typically, the rupture occurs posteriorly because the annulus is thinnest there and pressure is applied on the spinal nerve. Spinal nerve pressure, or irritation to surrounding structures, is the cause of the pain. The third condition is a chronic circumferential bulging which causes joint instability and compressed nerve roots.
Spinal column
Spinal nerve
Herniation Annulus fibers Nucleus pulposus
Figure 15.8 Schematic drawing of the spinal cord showing a herniated disk. Herniation is usually caused by a tear in the annulus fibers and results in the nucleus pulposus rupturing out through the annulus. This places pressure on the spinal nerve causing low back pain.
15.3.1 Nonablative Treatments Pain Management
Section No. Title 13 Pain management is done using exercise, heat, massage, and medication. This type of therapy is more conservative and is considered the first line of treatment. Spinal Fusion Spinal fusion occurs when an intervertebral disk is removed and adjacent vertebrae are fused together. This causes the vertebrae above and below the disk to grow together and form a single bone. This is typically a rather invasive surgery with a long recovery time. After a spinal fusion, a person is often limited from activities which cause a great deal of rotation of the spine due to the added stress on the vertebrae. 15.3.2 Radiofrequency Ablation The use of RF electrodes and RF lesion generator systems for the treatment of low back pain caused by intervertebral disks was introduced by Sluijter and Cosman in 1995. A needle is placed inside of the disk and heat is applied to destroy any nerves within the disk that may be causing pain (Sluijter and Cosman, 1995). Technique Impedance monitoring is used to insert the probe. The disk has substantially lower impedance than the normal surrounding tissue and therefore it can be easily recognized when the probe has entered the intervertebral disk. It is also possible to use stimulation to test the location of the probe within the body because the disk is not innervated and will not produce a response to stimulation. Figure 15.9 is schematic drawing of the setup. The needle electrode consists of a shaft with a pointed metal tip which is connected to an RF source. The RF lesion connection is monopolar (single active tip) with a reference electrode placed on the body's surface. The RF energy enters through the tip and returns through the body to the reference electrode.
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RF Z T
Skin
Figure 15.9 Schematic drawing of the RF probe ablation technique. The radiofrequency (RF) generator measures impedance (Z) as the probe is inserted into the disk. RF energy is applied to the center of the disk while the temperature (T) of the tissue is monitored. The connection is monopolar with a reference electrode placed on the surface of the skin. Adapted from Sluijter and Cosman, 1995.
Temperature, impedance, and power are monitored using control circuitry. The heat applied at the center of the disk spreads easily throughout the disk to its periphery due to the lack of vasculature. The core temperature of the disk is raised to 70 C. Bone above and below the disk act as a thermal insulator to keep heat within the disk. The vasculature on the periphery, however, causes the temperature to rapidly fall off at the edge of the disk. This keeps the other structures from being damaged (Sluijter and Cosman, 1995). Electrode Design Figure 15.10 illustrates the electrode design for this technique. It is similar to the standard RF electrodes used in other procedures. It has an outer cannula with an insulated shaft and an exposed tip that is pointed for penetration into the disk. Inside of the cannula is the stylet which extends down to the exposed tip of the cannula. The stylet contains temperature sensors and also allows for impedance monitoring. The stylet may be modified to extend beyond the length of the cannula, as well as have a curved shape, to monitor temperature and create lesions closer to the edge of the disk if necessary. special A feature of this electrode is that it has radiolucent hubs on the cannula and stylet which allow imaging along the direction of the needle with minimal artifacts from the hub (Sluijter and Cosman, 1995).
Section No. Title 15
Figure 15.10 Electrode design for RF probe ablation including the outer cannula with an insulated shaft (diagonal lines) and pointed, uninsulated tip. The inner stylet is shown by the dashed lines and extends down the cannula to the exposed tip. Adapted from Sluijter and Cosman, 1995.
15.3.3 Intradiskal Electrothermal Therapy (IDET) A treatment called intradiskal electrothermal therapy or IDET uses heat (either RF or laser) to burn away the invading nerves and seal the tears in the annulus rings (Marieb and Mallatt, 2001). Technique During the procedure, the patient is conscious and is given a local anesthetic. A hollow needle or introducer is placed into the symptomatic disk using fluoroscopic guidance. A catheter is navigated by the physician through the needle to the problematic area of the annulus (Figure 15.11). Force is used to advance the catheter while a twisting motion is used to control the orientation of the distal end inside of the patient. Unilateral or bilateral catheter deployment is used to cover the entire posterior annular wall. A temperature regulated generator controls the delivery of heat through the catheter.
Figure 15.11 Insertion technique for IDET. Adapted from Saal and Saal, 2000.
The intention is to have annular collagen shrinkage stabilize the annular fissures and to have thermocoagulation of native nociceptors and ingrown unmyelinated nerve fibers. The system provides temperatures between 55 and 65 C. With this level of heat, collagen remodeling and thickening occurs after treatment without scar tissue (Saal and Saal, 2000). Oratec Inventions SpineCATH
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The SpineCATH system uses a catheter similar to the one shown in Figure 15.12. The catheter dimensions can be found in Table 15.3. The bent tip of this catheter causes the intradiskal section to continue to bend the catheter in the same direction around the inside of the disk as the catheter is advanced. This is preferred for reaching the posterior side where most of the problems occur. The catheter must have enough strength such that it does not fall back on itself (Sharkey et al., 2001). The ORA-50 auto-temperature heat generator controls the catheter heat delivery system. A maximum catheter temperature of 90 C corresponds to a tissue temperature of 75 C (Saal and Saal, 2000).
Figure 15.12 Catheter design for Oratec Inventions. The probe can be maneuvered to bend as shown in this figure. The pointed tip allows for easier guidance of the catheter along the curved edge of the disk. Adapted from Sharkey et al., 2001. Table 15.3 Catheter and introducer specifications for IDET (Sharkey et al., 2001).
Specification Catheter diameter Catheter length Introducer length Value 2 5 mm 10 60 cm 5 50 cm
Candidates Ideal candidates for this therapy have had the following: chronic low back pain for more than 3 months, nonoperative treatments for 3 months without improvement, a normal neurological exam, a negative SLR (straight leg raise) for sciatica, a negative MRI scan for neural compressive disease, preservation of disk height, and no segmental instability (Saal and Saal, 2000). Degenerative disk disease has five stages. IDET is thought to work best for stages 3 or 4. Typically stage 1 and 2 are asymptomatic and stage 5 is too severe and requires spinal fusion (Sharkey et al., 2001). Results IDET offers patients a very promising option besides chronic pain management or spinal fusion. Cost, morbidity, and the currently observed degree of effectiveness
Section No. Title 17 make this an attractive alternative. The results of a study done by Saal and Saal are shown in Table 15.4. VAS refers to the visual analog pain scale score which is typically used in hospitals. This is a rating of the amount of pain that a person feels on a scale of 1 to 10, where 10 is the most pain. Sitting tolerance refers to the amount of time a person is able to sit comfortably.
Table 15.4 VAS and sitting tolerance results pre and post treatment. The VAS score represents the person's pain level on a scale from 1 to 10, with 10 being the most pain. The sitting tolerance refers to the minimum amount of time the person is able to sit in minutes (Saal and Saal, 2001).
Pretreatment mean VAS (0-10) Sitting tolerance (min) 7.32 23.6 Post treatment mean 3.58 47.2 Change in mean 3.74 23.6 Significance (P-value) P < 0.0001 P < 0.0002
15.3.4 Percutaneous Laser Disk Decompression (PLDD) Percutaneous laser disk decompression or PLDD is a treatment that was designed specifically for low back pain associated with a herniated disk. PLDD is a nonsurgical laser treatment first performed by Dr. Daniel Choy in 1986 (Laser Spine Center, 2002). Technique An 18-guage needle with an obturator is inserted into the herniated disk under fluoroscopic guidance. The obturator is replaced with an optical fiber that is connected to an Nd:YAG laser. Laser energy is sent through the optical fiber and vaporizes a small portion of the disk nucleus. The laser fires at 20 W with 1 s pulses and a partial vacuum is created which draws the herniated portion away from the nerve thus relieving the pain symptoms. Equipment An example of the fiber optic device used for this procedure is shown in Figure 15.13. The 18-guage needle or conduit consists of an outer tube and an inner tube. The optical fiber is inserted through the inner tube once the device is in place. The optical fiber connects to the Nd:YAG laser source. Fresh air is pumped into the inner tube along the optical fiber and is externally discharged with the vaporized material through the space between the inner and outer tube (Daikuzono, 1999).
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Laser connection Outer tube Optical fiber
Pressurized air Escaping air Inner tube
Figure 15.13 The fiber optic device for PLDD consists of two tubes. The optical fiber is placed in the inner tube along with the air which is being pumped in. The space between the inner and outer tube allows for the air and vaporized material to escape.
Results The PLDD procedure has been shown to have an 89% success rate with only a 0.4% complication rate. Most of the complications seen during an open procedure are eliminated by this technique. Due to the small needle, there is no scarring, and since only a tiny portion of the disk is being vaporized, no spinal instability results. The procedure is also less expensive than more conventional surgeries and has a shorter recovery time (Laser Spine Center, 2002).
15.4 Chronic Pain and Spasticity
Ablation can also be used to create lesions to disrupt neural pathways of healthy tissue to alleviate pain or spasticity. There are numerous disorders as well as ablative treatments in this area. Lesions of the neural pathway are often used as a last resort, since they may destroy other sensations or be a source of new pain. The primary procedures performed are discussed briefly in this section. Each lesion is made along the spinal pathway from the peripheral nerves to the brain or in areas of the brain thought to perceive the pain (Figure 15.14).
Section No. Title 19
Thalamus Cingulatomy Trigeminal rhizotomy
Cordotomy
Facet denervation
Selective dorsal rhizotomy Peripherial nerve neurotomy
Sympathectomy
Figure 15.14 The nerve pathway and general region of the various ablation procedures for chronic pain and spasticity.
15.4.1 General Denervation Denervation is the general term used to describe the destruction of nerves to eliminate pain. This procedure is commonly done to destroy peripheral nerves, an example of which is the nerves that innervate the facet joints. Facet joints are cartilage covered joints in the posterior part of the spine and contain a synovial lining which produces lubricating fluid. If the cartilage is damaged, the lubricating fluids can become trapped, the joints may be locked in an abnormal position, or the fibrous capsule surrounding the joint may be torn; all resulting in pain. Cryodenervation Cryoablation techniques have been used to treat neuralgias, post surgical pain, cancer pain, phantom limb pain, and facet pain. Cyrodenervation is an outpatient procedure with minimal complications. A needle is inserted under fluoroscopic guidance into the nerve area of interest. Unlike other techniques such as RF or laser ablation, this procedure can be applied to many different nerves including myelinated peripheral nerves. The cryoprobe uses nitrous oxide, carbon dioxide, or liquid nitrogen to lower the temperature to the range of 60 to 120 C and freeze nerves into an ice ball. For small nerves, the energy is applied for about 90 s to create a lesion. Several of these lesions are needed for larger nerves. This interrupts transmission along the nerve for up to three months (American Board of Interventional Pain Management). RF Denervation
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RF denervation (RF neurolysis) uses RF energy to temporarily destroy nerves for pain relief. On a separate visit before the procedure is done, local anesthetic is typically injected into the area to see what effect the lesion will have on the patient's pain. During RF denervation, high frequency energy is used to heat the nerve to above 65 C which destroys conduction through that nerve. After the RF energy is applied, the electrical conduction of the nerve is destroyed for 3 to 18 months. This is typically done on unmyelinated peripheral nerve fibers such as the nerves to the facet joints of the spine (American Board of Interventional Pain Management). Laser Denervation Laser denervation can also be used to treat the facet syndrome or facet joint pain. This procedure is similar to the cryo or RF ablation procedures but uses a holmium YAG laser to deliver low energy across the path of the nerve to disrupt the pathway. Although it is less commonly done than RF or cryo facet denervation, it has been shown to be faster and more efficient (American Board of Interventional Pain Management). Chemodenervation Chemicals may also be used to destroy the nerves. Injections of botulinum toxin A or phenol are examples of the chemicals used. Effects of chemodenervation typically last three to four months. It can be used to manage both pain and spasticity. 15.4.2 Cordotomy Often patients with cancer have extreme pain in their lower extremities. This pain can be treated by ablating the spinal tract responsible for transmitting impulses to the brain regarding pain and temperature. This procedure is called a cordotomy and is typically only used as a last resort to relieve pain in the final year of the patient's life as the pain tends to recur. This procedure can be done either open or percutaneously. Percutaneous procedures are more common and are done by inserting a needle just below the ear at the cervical level using fluoroscopic guidance. The lesion is made on the opposite side of the pain because the nerve pathways cross in the spinal cord (Gibson and Palmer, 1995). RF ablation is typically done with a small 0.1 to 0.5 mm electrode and has some technical limitations, especially in monitoring temperature. Lesion temperatures of 80 C and up are commonly used (Cosman, 1983). 15.4.3 Rhizotomy
Section No. Title 21 A rhizotomy is a surgical procedure that cuts the spinal nerve roots in order to interrupt the nerve pathways that relay pain impulses to the brain. Two common rhizotomy techniques that utilize ablation are trigeminal rhizotomies and selective dorsal rhizotomies, both of which are described below. Trigeminal Rhizotomy Trigeminal neuralgia is characterized by severe "lightning-like" stabs of facial pain. It can be caused by abnormal blood vessels that compress the trigeminal nerve or by the degeneration of the trigeminal nerve. When the pain cannot be controlled with medications or other pain therapies, a trigeminal rhizotomy may be recommended. This is an outpatient procedure where a needle electrode is introduced through the face into the nerve in the base of the skull. Radiofrequency current is used to selectively destroy pain nerve fibers while preserving touch sensation nerve fibers. Pain can occasionally recur after surgery in 20% of the patients (Neurosurgical Medical Clinic). Selective Dorsal Rhizotomy Selective dorsal rhizotomy is a neurosurgical technique used to treat spasticity, especially in children with cerebral palsy. For this procedure, a 5 to 8 cm incision is made along the center of the lower back. The sensory nerves and motor nerves are separated and the sensory roots are ranked for spasticity. Severely abnormal rootlets are ablated with RF energy. When the surgery is complete, the dura is closed and the sensory nerves are bathed in morphine. One side effect of this technique is sensory loss, numbness, or uncomfortable sensations in limb areas that the cut nerve supplied; however, these may disappear. Also, some patients may experience difficulty with bladder and/or bowel control after surgery (Westhoff). 15.4.4 Sympathectomy Sympathectomy is done to treat pain due to narrowed blood vessels or damage to peripheral nerves. This outpatient procedure is done under local anesthesia. The target of this procedure is the sympathetic ganglia which consist of collections of nerve cell bodies along the thoracic or lumbar spinal cord. The ganglia are located using X rays and stimulation. RF energy is then applied to destroy the ganglia, relieving pain in as many as 75% of patients (Health A to Z, 2003). 15.4.5 Cingulotomy Stereotactic cingulotomy using radiofrequency energy may also be used to treat pain, specifically as a last resort for cancer pain. This procedure involves lesioning the white matter deep to the cingulated nucleus. These pathways are important in
15-22 Chapter 15 Brain, Spinal and Nerve Ablation
emotion and motivation. Pain is relieved in 30 to 90% of cancer patients following cingulotomy or cingulotomy combined with midbrain tractotomy (the stereotactic ablation of the midbrain). This procedure may also be used to treat psychiatric disorders such as depression, schizophrenia, anxiety, obsessivecompulsive disorder, and Tourette's syndrom; however, its...