Seizure Disorders

Stereotactic methods, as applied to seizure disorders, encompass both the diagnostic and therapeutic realm. From the standpoint of diagnosis, implantation of stereotactic depth electrodes for localization of seizure activity in mesial temporal structures is a common technique. In some centers, especially in Europe, arrays of stereotactically implanted depth electrodes are used in preference to the surface grids commonly used in North America. Ablative stereotactic procedures have been used in...

Outcome

Many classification schemes have been proposed to assess outcome after surgery for intractable seizures. Perhaps the most popular is the four-tiered classification scheme developed by Engel 4 . The class 1 patients include those who are seizure-free for 2 years since surgery, those with occasional nondisabling simple partial seizures, and those with generalized convulsions only in the setting of antiepileptic medication withdrawal. Class II patients have rare (< 2-3 per year) disabling...

Normal Anatomy And Neurobiology 21 Spinal Cord Dorsal Horn

The dorsal root entry zone refers to the interface between the central and peripheral nervous systems in the spinal cord and specifically includes Rexed's laminae I-V, located in the posterior dorsal horn of the spinal cord. It is the pathway through which sensory afferents enter the central nervous system (CNS) during development and the area in which the first synaptic relay and integrative center for nociceptive afferents are located. Although laminae I-V each has a unique and discrete...

Mr Strategies

In general terms, attempts should be made to minimize distortion. Any hidden clips buried in long hair should be identified and removed. Impulse generators for deep brain stimulators should have their amplitude reduced to zero to prevent side effects. Higher field magnets are preferable, especially 1.5 Tesla and above. A protocol should be in place with the radiology department to ensure frequent calibration to minimize field heterogeneities. The Leksell frame is engineered to very high...

Introduction

In 1951 Lars Leksell coined the term stereotactic radiosurgery (SRS) 1 . A ceaseless innovator, his goal was to develop a method for ''the non-invasive destruction of intracranial . lesions that may be inaccessible or unsuitable for open surgery'' 2 . The first procedures were done using an orthovoltage X-ray tube mounted on an early model of what is now known as the Leksell stereotactic frame, for the treatment of several patients with trigeminal neuralgia. After experimenting with particle...

Surgery

The images are transferred to the operating room computer and the rods identified. If the MC is used, then the surgeon must enter the coordinates for each rod and for the target on the slice of interest. If need be, registration with a nonstereotactic digital image MRI, functional MRI, position emission tomography (PET), etc.) is done. Anteroposterior, lateral, and vertical settings for the stereotactic arc are derived. In the meantime, the patient is positioned, usually supine (or lateral for...

The Lesion Radiofrequency versus Laser

The classic DREZ lesion operation is performed using a radiofrequency electrode to heat the target tissue to 75 C for 15 seconds. Lesions are made approximately 1 mm apart, with great care to avoid disrupting the small vessels over the surface of the spinal cord or brainstem. Earlier investigators attempting to use CO2 lasers for DREZ lesioning found significant problems with small vessel disruption. Different electrodes are used for the spinal cord DREZ as opposed to the nucleus caudalis DREZ....

Amorphous Silicon Detectors

The Cyberknife localization method can, in principle, be used wherever radio-opaque features are associated with an anatomical target, a concept that would allow the extension of radiosurgical technique to extracranial sites. The Cyberknife has already been used to treat sites within the spine 9-11 , lung, and pancreas. 1.3.1 Limitations of Previous Cameras There are multiple shortcomings to the prior imaging system used by the Cyberknife. As previously configured, the X-ray sources used with...

Criticisms Of Radiosurgery

Radiosurgery was initially viewed as a competitor to traditional neurosur-gical techniques. Common criticisms of radiosurgery included the following (1) The tumor is not removed (2) There is no rapid reduction in mass effect (3) Future surgery will be more difficult (4) Additionally, patients may have a false sense of cure. It is true that the tumors often are not eliminated, but the goal of radiosurgery is tumor control, not extirpation. A rapid reduction in mass effect is often not required,...

Info

Resection of metastatic lesions can be accomplished efficiently and safely with image-guided surgery. A report of the first 41 patients operated on using the Mayfield ACCISS system showed an average time for the procedure of under 2 hours with minimal morbidity 10 . The Mayfield ACCISS for transphenoidal surgery eliminates the need for fluoroscopy. One can track the probe in the axial and coronal views as well as the sagittal view (Fig. 4). Even with the traditional use of fluoros-copy, one...

Planning

Without doubt, target localization is the most important step in movement disorders surgery, the goal of which is to lesion the brain as effectively as Figure 1 Neurological Surgery Planning System (NSPS) functional surgery module showing the correlation between the patient's anatomical imaging study and the Schaltenbrand's stereotactic atlas. Figure 1 Neurological Surgery Planning System (NSPS) functional surgery module showing the correlation between the patient's anatomical imaging study and...

Relative Cost Of Ablation Versus Stimulation

Many of the costs associated with the creation of an ablative lesion and placement of a deep brain stimulator are similar (Table 2). These include preoperative imaging, operating room time for burr hole creation and target identification and hospital stay. The time difference between that needed for Table 2 Costs of Ablation Versus Deep Brain Stimulation Table 2 Costs of Ablation Versus Deep Brain Stimulation

Indications 21 Adults

Candidates for CC include patients with medically intractable primary generalized epilepsy or partial epilepsy with rapid secondary generalization that is either unlocalized or localized to unresectable cortex. Differentiation be tween these two groups is often difficult, although relevant, in that patients with lateralized electroencephalograph findings often have a better outcome 5,6 . The most common generalized epilepsies treated with CC are characterized by atonic or akinetic seizures,...

Stn

Vertical -4 to -6 Lateral 12 AP 2 to 3 posterior to MCP Abbreviations Vim, Ventralis intermedius GPi, Globus pallidus internal STN, Subthalamic nucleus AP, Anteroposterior MPC, Midcommissural point. Abbreviations Vim, Ventralis intermedius GPi, Globus pallidus internal STN, Subthalamic nucleus AP, Anteroposterior MPC, Midcommissural point. thalamic surgery for tremor relief, for example, prominent leg rather than arm tremor might dictate a slightly more lateral approach in Vim 8 . 2.2 Use of MR...

References

Stereoencephalotomy. Part 1. New York Grune & Stratton, 1952. 2. L Leksell. Stereotaxic radiosurgery in trigeminal neuralgia. Acta Chir Scand 137 311-314, 1971. 3. L Leksell. Stereotaxis and Radiosurgery An Operative System. Springfield, IL Charles C. Thomas, 1971. 4. RN Kjellberg, AM Koehler, WM Preston, WH Sweet. Stereotaxic instrument for use with the Bragg peak of a proton beam. Confin Neurol 22 183-189, 1962. 5. JL Barcio-Salario, H Roldant, G Hernandez....

Radiosurgery

Perhaps no more important method of treating brain tumors has been introduced in the last 20 years than stereotactic radiosurgery. Radiosurgery uses precise delivery of energy in the form of convergent beams of high energy photon or charged particle radiation to tumor tissue on a hypofractionated basis. Devices designed to deliver radiosurgical doses include the Leksell Gamma unit and a number of linear accelerator-based devices. Radiosurgery has been found to yield survival rates comparable to...

Intraoperative Ct

Digital imaging in the neurosurgical OR was first done using CT, where a dedicated unit was installed at the University of Pittsburgh 11 . In general, CT scanners are less expensive than MRI units, but acceptance of this technology has been limited by several factors. These include the lower soft tissue contrast compared to MRI, bone hardening artifact in the posterior fossa, the use of ionizing radiation, and likely need for a dedicated technologist to operate the system. Nonetheless, the...

Treatment

A single, completely satisfactory method of treating trigeminal neuralgia in all patients has yet to be described. In all cases the initial therapy should be medical. Carbamazepine (Tegretol) and phenytoin (Dilantin) are the two drugs that have traditionally shown the greatest promise for patients with trigeminal neuralgia. Baclofen (Lioresal) may be useful in the treatment of patients whose pain has become refractory to treatment with carbamazepine or phenytoin 3 . Treatment with gabapentin...

Dose And Collimator Size

Doses used for functional stereotactic radiosurgery have traditionally been high and the volume small 9 . This has stemmed from two concepts (1) a high dose is needed to create a well-defined lesion with an area of necrosis with a short time-frame to benefit, and (2) the nerve tracts to be treated are usually small in diameter and, consequently, in volume. Kihlstrom, in reporting the Karolinska experience 10 , of SRS for obsessive compulsive and anxiety neuroses, noted that when using a dose of...

Postimplantation Programming

The programming of the SCS system may be performed soon after the patient's awakening from the general anesthesia. Obviously, stimulation parameters similar to those that were tested during the trial may be used. Some electrode configurations, however, are technically impossible during the stimulation trial. The best example is monopolar stimulation, when one of the electrode contacts is active and the IPG case serves as a reference. This mode allows for a lower stimulation voltage compared...

The System

BrainLAB VectorVision is an intraoperative, frameless, image-guided navigation system. The system integrates preoperative computed tomographic magnetic resonance imaging (CT MRI) digital data, with real-time movement or position of surgical instruments. The navigation is based on reflective markers detected by infrared cameras 6 . The surgeon is able to point targets dynamically selected, in a frame-less environment. The whole system in use at our institution is contained within a trolley that...

Radiosurgery Treatment Planning

Subsequent to localizing the target volume from a three-dimensional stereotactic database, these images are used to develop a radiosurgery dose plan. Our philosophy is to design treatment plans in which the isodose shell is tightly conformal to the target volume, while all normal tissue is excluded from the high-dose region. Because radiosurgery is used to treat benign lesions and as a boost for malignant disease, no margin is added to the gross target volume to irradiate microscopic disease....

Pain

The current generation of deep brain stimulation electrodes was initially conceived and devised for use in treatment of chronic pain. Currently, DBS is limited to a few specialized centers treating pain syndromes unresponsive to all other modes of therapy. Because of the subjective nature of pain and the pervasive coincidence in these patients of significant psychiatric overlays, objective analysis of the results from surgical intervention is extraordinarily difficult. Most of the published...

Patient Selection

When considering the goal of neurosurgical intervention, spastic cerebral palsy patients can be divided into two groups. The first group is composed of those patients in whom functional improvement is expected. An example would be a spastic diplegic 5 year old who walks independently with a scissoring gait, flexed hips and knees, and an equinus foot posture. There should be no evidence of dystonia and minimal fixed contractures. Although range of motion may be limited in straight leg raising...

Operative Procedure

Once the preliminary test doses have established therapeutic efficacy, the patient may be scheduled for implantation of the pump. The patient must be free of any potential infectious sources, including urinary tract infections and open decubitus ulcers conditions frequently found in this patient group. Implanting a Synchromed Infusion System (Medtronic) is a sterile surgical procedure taking approximately 2 hours (Fig. 1). It may be performed under general, regional, or local anesthetic. The...

Nociceptive Pain

When pain is considered to be compatible with tissue damage associated with an identifiable somatic or visceral lesion or injury, it is known as nociceptive. Nociceptive pain originating from somatic structures (skin, muscle, connective tissue) is typically well localized, sharp, aching, or throbbing. In contrast, visceral pain is generally less well localized but may have a specific referral pattern. If a hollow viscus is obstructed, the pain may be gnawing or cramping in nature, whereas if an...

Adjunctive Alpha Agonists

When the use of the spinal anesthetics in a patient with chronic pain is ineffective or intolerable, changing the adjunctive therapy to an alpha-2-adrenergic agonist may prove successful 18 . Within this drug class, clon- idine, tizanidine, and dexmedotomidine have been used, but clonidine is the most common of these agents. It is thought to produce analgesic effects by inhibition of substance P release, thereby inhibiting nociceptive neurons 18 . Clonidine has been found to potentiate the...

Intraoperative

Intraoperative imaging with MRI (iMRI) is being accomplished with systems that meet the needs of the neurosurgical OR in different ways. The ideal iMRI will provide the best possible images, create the least amount of interference with the OR as possible, include a means of stereotactic navigation, and be as versatile as possible. The first iMRI was built at the Brigham and Women's Hospital in Boston as a collaborative effort between the Neurosurgery and Radiology departments and General...

Ultrasound

Ultrasound (US) has been used in neurosurgery for over 20 years 13 . Its major limitation has been image quality and the need to image through the open skull. Neurosurgeons accustomed to interpreting CT and MR images may not readily understand the US images that reflect echogenicity, and items such as cottonoids that have an echo must be removed before imaging. Interpreting the two dimensional images in a 3D manner may also pose problems. Still, a useful iUS system is attractive because it has...

Adjunctive Anesthetics

Synergistic antinociceptive activity has been displayed by the addition of local anesthetics to intraspinal opioids. They act by different mechanisms, primarily blunting neuroexcitability within the spinal cord. Bupivacaine is most frequently used because of its long duration of action, but tetracaine 18 and lidocaine also have been studied. The addition of bupivacaine not only improves pain control but can decrease morphine requirements, thereby Figure 1 Initiating intrathecal therapy. Figure...

Pump Selection And Surgical Technique

There are many different techniques for long-term intrathecal drug administration (Table 1). The simplest methods include external and tunneled catheters and subcutaneous ports. These are often inserted by anesthesiologists and serve best for intra-axial trials and short-term management of intractable pain. Neurosurgeons may be called to help with insertion of these catheters if patients have complicated spinal anatomy and need laminectomy for intraspinal access. More commonly, however,...

Review of Safety and Efficacy

Clinical experience with vagus nerve stimulation began in 1988 with the first human implantation of the NCP system. Since then, more than 1,000 Figure 1 Schematic representation of VNS therapy. A pulse generator inserted in the subcutaneous tissues of the upper left chest delivers intermittent electrical stimulation to the cervical vague nerve trunk via a bifurcated helical lead. Reproduced with permission from Cyberonics, Inc. Figure 1 Schematic representation of VNS therapy. A pulse generator...

Indications For Using The System

The system can be used for functional neurosurgical procedures including implantation of deep brain stimulators, biopsy of intracranial lesions, brachytherapy, aspiration of cysts, aspiration of brain abscesses, stereotactic craniotomies, and radiosurgery. Figure 4 Computed tomographic image with coordinate measurements. The two arrows mark the fiducial markers. 1-Y coordinate (perpendicular distance from the target to the horizontal line joining the two fiducial markers), 2-X coordinate...

Retrogasserian Glycerol Rhizolysis

Results from the first series of patients treated by glycerol rhizolysis were published by Hakanson in 1981 6 . Previously, glycerol was used in mixtures containing ethanol or phenol for the rhizotomy procedure. The observation that glycerol alone was effective for the treatment of trigeminal neu- Figure 2 Point of needle in the foramen ovale. A gloved finger prevents penetration of the oral mucosa. Figure 2 Point of needle in the foramen ovale. A gloved finger prevents penetration of the oral...

Discussion

At the New Jersey Medical School we have used the StealthStation for over six years. At first, use of the StealthStation seemed like a cumbersome addition to the OR and added at least two hours to any procedure. With further experience the system became a completely routine part of surgery and its use is transparent to OR and radiology staff. All of the neurosurgeons in our group are comfortable with its use. Concerns have been raised that residents will come to rely on this technology to the...

Stereotactic Craniotomy

Recent advances in imaging coupled with the availability of high-performance computing has made possible the introduction of stereotactic-assisted craniotomy for tumor, vascular, and other mass lesions. These stereotactic methods were initially introduced by Kelly, using a frame-based stereotactic system 16,17 , and have since been moved to so-called frameless systems by a number of other groups 18,19 . Frameless systems differ fundamentally from their frame-based counterparts. Frame-based...

Neuropathic Pain

In contrast, neuropathic pain is believed to be associated with sustained activity at a site of aberrant somatosensory processing in the peripheral or central nervous system resulting from neural injury or irritation. Typically, neuropathic pain persists long after the precipitating event. Neuropathic pain is clinically diverse. Patients may describe unfamiliar burning, electric shock-like or shooting dysesthesias, which may be spontaneous or evoked by movement. Examination may reveal...

Myoclonic Seizures

Myoclonic seizures usually begin during the early teenage years. A my-oclonic jerk is a brief shock-like contraction of an individual muscle or a muscle group. These jerks usually involve the limbs but may be confined to the face or trunk. Generalized myoclonic jerks or jerks involving the legs can be disabling, because they are associated with violent falls and frequent fractures. Myoclonic seizures have a circadian pattern and commonly occur in the morning shortly after awakening. Patients...

Complications

Complications related to DREZ lesioning fall into two major categories underlesioning and overlesioning. Underlesioning is a problem that continues to be addressed and, with continued improvement in the electrodes and RF lesion generator, are decreasing in frequency. Overlesioning, on the other hand, can have serious consequences, especially in the case of the spinal cord DREZ lesion. Complications of over-lesioning range from sensory deficits to severe motor deficits, including paraplegia and...

MRI with the ZD Frame and Localizer

The Z-D frame can be used along with the specific localizer for MRI image acquisition. It is extremely important to generate images parallel to the AC-PC line for use in the planning process. In almost all cases, we recommend CT and MRI scans for image correlation, using skin fiducial markers (IZI Medical Products, Baltimore, Maryland) in several locations on the scalp. The initial step includes taking a T1-weighted sagittal scout to identify both anterior and posterior commissures and to...

The Operating Room

There are several ways to organize the operating room. We use the cameras attached to the computer trolley, placing the trolley between the neurosurgeon and the anesthesiologist. In any position, the trolley should be in the surgeon's visual field, and the cameras about 1 to 2 m from the patient's head. The two cameras can be moved freely as a unit during surgery. The cameras ought to have an unobstructed view of the star-shaped Mayfield adapter. When the operating microscope is to be used, the...

Chronic Pain

Chronic pain was among the first conditions treated with the Gamma Knife 1 . In the 1990s, we developed a technique to perform medial thalamotomy using stereotactic magnetic resonance imaging (MRI) localization and the Gamma plan computer dose planning system 2 . The target includes portions of the medial dorsal, intralaminar, center median, and parafascicular thalamic nuclei. Lesions are now made with a single isocenter using the 4mm secondary collimator helmet of the Gamma Unit and maximum...

Postoperative Care

The patient is generally kept in the hospital for an additional 24 hours for administration of intravenous antibiotics, and a program for tapering off any oral baclofen is begun. This taper off oral medications should be accomplished gradually as the side effects of abrupt withdrawal, as mentioned above, are severe. Sutures are removed at 10 days after operation. Depending on the amount of drug required by the patient, the pump is refilled, usually by a home nursing service, every 4 to 6 weeks....

Spasticity And Cerebral Palsy

Spasticity in childhood is most commonly encountered as a feature of cerebral palsy, which results from an insult to the developing brain. Cerebral palsy may be classified by the type of motor involvement (spastic, dystonic, or mixed), or by the distribution of involvement (quadriplegia, diplegia, hemiplegia). Loss of fine motor control, impaired balance, weakness, and delayed motor milestones also occur. The progressive, deforming forces of spasticity can lead to secondary muscle contractures...

Future Directions Of Xknife Technology

This chapter has emphasized the open architecture of the LINAC-based X-Knife treatment platform for both SRS and SRT. As this technology evolves in its response to ineluctably broader applications, new refinements promise to provide more effective treatments for challenging intracranial targets. As examples, optic nerve sheath meningiomas were originally considered inoperable and untreatable, but our initial experience with conventional fraction SRT has suggested promising tumor control with...

Pathophysiology Of Neuropathic Pain

Many theories have been proposed for explaining the pathophysiology of chronic pain after injury to peripheral nerves, dorsal roots, or dorsal root ganglia. The various proposed mechanisms of chronic pain production remain controversial, but it is generally accepted that hyperactivity in noci-ceptive pathway neurons as well as neuronal hypersensitivity to abnormal discharges from injured peripheral ganglia or neurons are involved in the pathophysiology of chronic neuropathic pain. When a...

Summary

The Voyager navigation system is the product of evolutionary development that provides simple, yet flexible and powerful navigation in the head and Figure 9 Many screen parameters may be adjusted for individual windows or the entire workspace. Colors and transparency of overlays may be stored as user preferences. Figure 9 Many screen parameters may be adjusted for individual windows or the entire workspace. Colors and transparency of overlays may be stored as user preferences. spine. The system...

Complications and Recurrence

Complications seen from percutaneous ablative therapy for trigeminal neuralgia have been extensively documented. The oral mucosa may be penetrated during the approach, resulting in bacterial meningitis or brain abscess. A carotid-cavernous fistula may result from injury to the internal carotid artery. There is a possibility of otalgia from eustacian tube dysfunction, or temporomandibular joint tenderness along with jaw weakness. Aseptic meningitis has been reported, as well as intracranial...

A

The clamp is attached to the Mayfield holder under nonsterile conditions. The star-shaped tool may then be screwed to the clamp with sterile gloves and detached if needed. Accuracy of reattachment is within 0.1 mm. Figure 3 Mayfield adapter. The clamp is attached to the Mayfield holder under nonsterile conditions. The star-shaped tool may then be screwed to the clamp with sterile gloves and detached if needed. Accuracy of reattachment is within 0.1 mm. least three...

The Future of CC

The vagal nerve stimulator (VNS) has been proven efficacious at reducing seizure frequency for partial seizures 19-21 and may be useful in primarily generalized epilepsy as well 22 . Long-term results appear promising 23 . Data are lacking on the relative success of VNS compared with CC for controlling generalized epilepsy, but the advantage of the VNS is a significant reduction in operative morbidity and decreased neuropsychological sequelae. Although seizure control will probably not be as...

Data Transfer

Datasets from the MRI and CT are transferred via network to the BrainScan planning computer. A backup system of data transfer by optical disc or tape is available in case online communication breaks down. Tape or disc data transfer can be used by medical centers where direct data transfer is not available. After transferring the MRI and CT data, the first planning step is the identification and localization of the fiducial rods of the CT localizer. The software requires manual identification of...

Accuracy And Error

Certain terms should be defined in discussions of any stereotactic system. Unbiasedness is a lack of skew. Precision is a tendency to approach a certain value. Observations may be precise (minimal spread from a mean value) but biased (that mean value is not the true value). Accuracy requires both unbiasedness and precision. In an article about three-dimensional digitizers, Wohlers describes the confusion about accuracy in his sidebar How Accurate is Accurate '' Comparing the accuracy of 3-D...

Conclusions

Surgery is a useful method, and sometimes the only one, to treat patients with various movement disorders. The advent of implantable DBS electrodes has made this surgery much safer and probably has improved the control of abnormal movements as well. For most patients at this time, DBS is preferable to lesioning. Coupled with the other advances in stereotactic technology, it may be tempting to view these procedures as ''routine.'' However, this is not so. The Vim nucleus is a relatively large...

D E K K E R

Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress. This book is printed on acid-free paper. 270 Madison Avenue, New York, NY 10016 tel 212-696-9000 fax 212-685-4540 Hutgasse 4, Postfach 812, CH-4001 Basel, Switzerland tel 41-61-260-6300 fax 41-61-260-6333 The publisher offers discounts on this book when ordered in bulk quantities. For more information, write to Special Sales Professional Marketing at the headquarters...

Imaging

During image acquisition, the base ring provides the attachment for the image localizers. Intraoperatively, the base ring acts as a head holder when used in conjunction with the Mayfield head holder and or the Sugita adapter. For CT and MR imaging, adapters provide an isocentric relationship with the CT gantry and the MR imaging head coiler. Independent of the type of interfacing method selected between the imaging studies and the base ring (isocentric or localizing), the reference for target...

Generalized Seizures

Generalized seizures are characterized by an abrupt loss of consciousness. Generalized seizures with motor activity include tonic-clonic seizures, my-oclonic seizures, tonic, or clonic seizures. Generalized seizures without motor activity includes absence and atonic seizures. Generalized seizures frequently have a genetic basis, and it is important to ask about a family history. The type of generalized seizure is age dependent. Absence seizures occur in children younger than age 10, myoclonic...

Dose Planning

Gamma Knife dose planning uses one or more (sometimes many) small isocenters of radiation to create a conformal plan that encompasses the lesion and minimizes the dose received by surrounding structures. The Gamma Knife provides 4-, 8-, 14-, and 18-mm collimators. Similar conformal plans can be designed from one or more large isocenters or from the combination of a greater number of smaller isocenters. The plan created with the larger isocenters will deliver an equivalent dose of radiation, but...

Vi

Age < 50 KPS > 90 Age < 50 KPS < 90 Age > 50 KPS > 70 at least partial surgical resection able to work Age > 50 along with KPS < 70 normal mental status or KPS > 70 at least partial surgical resection not able to work KPS > 70 biopsy only and dose > 54.4 Gy Age > 50 along with KPS > 70 biopsy only and dose < 54.4 Gy Age > 50 KPS > 70 more than 3 months of symptoms Age < 50 abnormal mental status Age > 50 KPS > 70 no more than 3 months of symptoms RTOG,...

Frame Application

In this era of frameless stereotaxy and emerging intraoperative imaging technologies, stereotactic frames still have their place. They are necessary for the performance of functional surgery, including placement of deep brain stimulators 2 . Brain biopsies arguably are done with the most accuracy and least time using a frame. Stereotactic radiosurgery is always done with a frame except in the unique case of the CyberKnife 3 . Craniotomies may be done in the frame, although frameless stereotaxy...

Methods Of Lesioning

The most common technique for creation of a permanent lesion is that of radiofrequency (RF) thermocoagulation, developed in the 1940s and 1950s 77,78 . Alternating current at radiofrequency (approximately 500,000 Hz) is passed through a monopolar electrode at the lesioning site, to a large surface area dispersive electrode taped to the patient's skin. In the immediate region of the active electrode, the rapidly oscillating electrical field produces movement of electrolytes that is sufficient to...

Neurophysiological Localization

Before placement of chronic stimulating electrodes or lesioning a target, neurophysiological localization is performed. At our center, we have shared in the development of the Radionics NeuroMap neurophysiology station. Figure 2 Fused magnetic resonance image on the Stereoplan workstation showing trajectory for placement of subthalamic nucleus stimulating electrode. Figure 2 Fused magnetic resonance image on the Stereoplan workstation showing trajectory for placement of subthalamic nucleus...

General Principles

The stereotactic approach to intracranial targets involves the rigid application of a stereotactic frame, a localizer, and an image data set derived from either CT, MRI, or angiography. With a fixed relationship between the patient's head and the fiducial localizers 3 , any intracranial target can be reached with an optimal trajectory and great accuracy. The standard performance specifications for cerebral stereotactic systems, specified by the American Society for Testing and Materials,...

Linac Experience

Functional SRS will constitute only a very small proportion of the treatments rendered in any Linac-based radiosurgery program. Few articles has been published on it over the last 5 years in the English literature 13 . In our own experience of more than 530 cases in 8 years, we have treated six patients for primary trigeminal neuralgia (TN) (excluding those whose presentation related to, for example, a petrous ridge meningioma). Thus, the description of treatment procedure will focus on that...

M

Figure 4 The five diagrams demonstrate the principles of using a mul-tileaf collimator (MLC) for intensity modulated radiotherapy (IMRT) delivery. A predetermined amount of radiation is delivered at each segment (leaf pattern) of a single portal. Associated with each segment is a fraction of monitor units reflecting the relative amount of dose to be delivered by each particular pattern. In static MLC (SMLC) delivery, the beam is off as the leaves move between segments. In dynamic MLC (DMLC)...

Tolerance Addiction

Many practitioners are hesitant to resort to intrathecal opioid administration because of unrealistic fears of tolerance, physical dependence, or addiction development. Analgesic tolerance is defined as a situation in which exposure to the opioid itself causes higher dosages to maintain the same level of analgesic effect. Early intrathecal animal models have shown that after only 7 days of repeated bolus doses of intrathecal morphine in primates, no effects of the drug could be seen 23 ....

Clinical Experience with Extracranial Lesions

A primary objective behind the development of image-guided radiosurgery was the ability to treat extracranial lesions. With the implementation of an amorphous silicon camera system, achieving this goal has become feasible. Because most extracranial lesions within the thorax and abdomen typically move with respiration, that is, are not fixed with respect to bony structures, a system for target localization has been developed that relies on implanted fiducials, respiratory gating, and target...

Treatment Delivery

As the preceding section demonstrates, highly conformal dose plans can be generated using the Linac Scalpel. Therefore, it is important that the dose delivery system is capable of accurately delivering these conformal plans. Unfortunately, a standard radiotherapy linac is not necessarily capable of achieving such accuracy the basic acceptance criteria for a radiotherapy linac requires that the gantry maintain a radiation focus about isocenter to an accuracy of 1 mm. In other words, the gantry...

Company Information

Radionics, Inc., USA Headquarters, 22 Terry Avenue, Burlington, MA 01803, (888) RSA-SERV, www.radionics.com Elekta Instruments, Inc., 3155 Northwoods Parkway NW, Norcross, GA 30071, (800) 535-7355, www.elekta.com COMPASS International, Inc., (formerly Stereotactic Medical Systems, Inc.), Cascade Business Park, 919 37th Avenue NW, Rochester, MN 55901,

Chorea

Chorea describes brief, abrupt, irregular, unpredictable, involuntary muscle contractions that are nonrhythmic, unpatterned, and have variable timing. Commonly involved are the distal parts of the extremities and the orofacial muscles. Chorea may appear as a symptom of Huntington's disease or other neurodegenerative disorders or may be secondary to other system diseases (Table 3). Early experience with a modest number of patients showed both pallidotomy and thalamotomy to improve contralateral...

Indications And Prognostic Factors

The conditions that respond favorably to DBS include failed back syndrome, causalgia, radiculopathies, peripheral neuropathies, trigeminal neuropathies, and phantom limb pain 10-12 . Conditions that respond poorly to DBS include paraplegic pain, thalamic pain syndromes, and postherpetic neuralgia. In general, nociceptive pain responds more favorably to PVG stimulation, whereas neuropathic pain responds to STh stimulation. Patients with pain syndromes who have had multiple operations to a given...

Base Ring

The base ring acts as a reference system and intraoperative head holder. The base ring can be made of aluminum, which is CT and X-ray compatible, carbon fiber, which is compatible with all imaging modalities (CT, X-ray, MRI, positron emission tomography (PET), or titanium, which is CT, X-ray, MRI, and convergent beam irradiation (CBI) compatible. The Z-D unit includes an open base ring, three or four pin holders that can be positioned at any desired location, and a set of 18 pins in five...

Electrode Implantation Technique

The procedure of electrode implantation for SCS is fairly straightforward. Percutaneous (wire) electrodes are inserted through a needle. A standard 18-Ga Tuohy needle is supplied with the electrode and comes with a stylet. The needle is inserted into the epidural space under fluoroscopic guidance after the tissues are infiltrated with a local anesthetic solution. Usually, a slightly paramedian entry point is preferred to avoid midline placement of the fragile electrode, where it may be damaged...

Diagnostic

Biopsy is the most common indication for the use of stereotactic methods. Before the introduction of modern stereotactic methods, biopsies involved free-hand needle aspiration or craniotomy guided by indirect radiographic procedures, such as angiography or ventriculography. Modern imaging and frame-based stereotactic procedures rapidly obtain diagnostic material with minimal patient mortality and morbidity 3,4 . The vast majority of brain lesions visible on imaging studies can be safely...

Point Definition And Registration

Two common methods for defining points are surface-based and point-based registration. Each offers a distinct set of advantages and disadvantages. Surfaced-based registration fits a set of points from the contours of one image to a surface model from contours of the patient's head or from other images. An advantage of this system is that it allows retrospective registration from prior images. Its disadvantage, however, is that it is less accurate. Point-based registration involves selecting...

1

Figure 2 Screen from image-guided navigational workstation showing the positioning of a formulaically-calculated target for a pallidal procedure using the workstation software. Figure 2 Screen from image-guided navigational workstation showing the positioning of a formulaically-calculated target for a pallidal procedure using the workstation software. allow estimation and consideration of potential image distortions (as with MR), or to allow consideration of different types of information...

Application

General preoperative precautions are followed as in any stereotactic operation 6 . In particular, normal coagulation profiles are clearly required. An- ticoagulated patients receive intravenous heparin for 5 days before surgery. The frame is placed orthogonally to the midsagittal plane by advancing the ear bars symmetrically through the lowest side holes into the external auditory meati. Salcman suggests placing the frame off center, with the ear contralateral to the target abutting the side...

Indications For

SRS has evolved from an esoteric treatment to an option that should be offered to many patients with intracranial lesions. The older or more medically fragile the patient, the smaller the target. The more hazardous the surgical option, the more SRS should be offered as an alternative to surgery, or as the primary treatment. Radiobiology suggests that there is a particular advantage for single-session irradiation of benign tissues 20 . Thus, certain patients with AVMs, acoustic neuromas, and...

Arc Selection

The dose-limiting structure is the brainstem, along with the constraint imposed by the dose rate of the Linac. Thus, to give 70 Gy with a maximum of 10 MU (monitor units) per degree of arc and less than 1 cGy per MU at isocenter, a total of more than 700 of arc rotation is required. This results in multiple short arcs 7-10 , given the small collimator size. Some of the arcs may need to be treated more than once because of the large MU per degree required. This situation is exacerbated by the...

Conclusions And Future Developments

The BrainLab stereotactic planning system is versatile and can plan radio-surgery with dynamic noncoplanar arcs or with conformal fixed beams. To be able to plan and treat all kinds of lesions efficiently, it is necessary to have the means of delivering both classic arcs and fixed conformal beams. Most of the drawbacks of previous versions of the BrainLab planning system have been corrected or improved in the present version, particularly the image fusion process, which is now reported to be...

Intensity Modulated Radiotherapy

The term ''intensity modulated radiotherapy'' is relatively new, although the concept of deliberately creating a non-uniform radiation beam to achieve a superior dose distribution is not. Modulation of heavy particle beam with a variable column of water or Lucite model in the beam pathway has allowed the placement of the Bragg Peak in tumors and vascular malformations since the early 1950s Kjellberg et al, 1964 Koehler et al, 1977 Tobias et al, 1956 . These techniques are not effective,...

Children

In the pediatric age group, one must balance the potential disruption of cortical reorganization mediated by the intact corpus callosum with the potential excitotoxic injury of persistent frequent seizures in the developing brain 7 . The consensus is that early surgery is indicated, depending on the severity of the seizures 7 . Indications in this age group are similar to the adult, although there is a higher proportion of patients with hemispheric disease, such as infantile hemiplegia,...

Egx

Figure 2 Location of lumbar incision. Figure 2 Location of lumbar incision. additional CSF leakage. The subcutaneous pocket is developed on the anterior abdominal wall, above the rectus fascia. The pocket should be positioned sufficiently below the rib cage and above the iliac crest so that when the patient bends, the pump will not strike up against the lowest ribs or crest, causing discomfort. A larger pocket is desirable, so that the edge of the pump does not place undue pressure on the...

The Localizer

This unit consists of an arc quadrant that can be mounted in any of four positions on the base ring at 0 , 90 , 180 , or 270 . The arc settings include three linear scales (a, b, c) and two angular scales (d, e). The first three correspond to the traditional x, y, and z spatial orientations. The last two are for modifying the entry point of the surgical trajectory according to the location of the lesion, vascular structures, and skull bone. The arc has two types of instruments holders, one for...

Frame And Components

Leksell's eloquent description of his system, as quoted by Lundsford et al. 3 , is difficult to improve on. Essentially, it consists of a semicircular arc with a movable probe carrier. The arc is fixed to the patient's head in such a manner that its center corresponds with a selected cerebral target. The electrodes are always directed toward the center and, hence, to the target. Rotation of the arc around the axis rods in association with lateral adjustment of the electrode carrier enables any...

Image Acquisition

Magnetic resonance imaging and CT are obtained for all patients (except for patients for whom MR imaging is contraindicated). The MRI is performed before placing the stereotactic head ring. For convenience, we perform the MRI one to several days before the planned radiosurgery, although it could be done on the same day as the radiosurgery before head-ring fixation. Magnetic resonance imaging data can be acquired and transferred to the planning system in axial, coronal, and sagittal planes,...

Surgical Technique

Georg Schaltenbrand

For the purposes of implantation of a deep brain electrode, any of the several commercially available stereotactic frames can be used. In North America today, the most popular stereotactic frames are CRW (Radionics, Burlington, MASS) and Leksell (Electa, Atlanta, GA). The procedure is completed in two stages. The initial stage is dedicated to implanting an electrode at the desired target site, and at a second stage, after a trial stimulation, the system is internalized using a fully...

History

Division of the corpus callosum for the treatment of patients with seizure disorders dates back to the observations of Van Wagenen in the 1930s 1 . He noticed that patients with strokes affecting the corpus callosum often had improvement in the frequency of their attacks. Experimental evidence for the importance of commissural fibers for the spread of epilepsy was demonstrated in the primate by Erickson, lending further support for this therapeutic approach 2 . Additional reports by Bogan in...

V

Figure 1 Using the appropriate collimator diameter with the standard nine-arc set results in a highly conformai dose distribution. The 80 , 40 , and 16 of maximum isodose lines are shown on three orthogonal MRI slices through the center of a nominally spherical meningioma. conforms to the shape of the target. Linac radiosurgery provides several treatment planning parameters that allow production of nonspherical treatment plans. Arc weighting, collimator size, and arc length may all be altered...

Complex Partial Seizures

During a seizure, it is important to determine whether the subject experiences an alteration or loss of consciousness. This implies spread of the epileptic discharge across the corpus callosum to the opposite hemisphere. Patients may describe a subjective feeling or aura before losing consciousness. If the epileptic discharge does not progress, the aura constitutes the simple partial seizure. Common temporal lobe auras include a rising epigastric sensation, fear, deja vu, jamais vu, and a...

Absence Seizures

The essential feature of an absence seizure is the sudden, abrupt loss of consciousness. Seizure onset is characterized by immediate behavioral arrest, and patients are noted to have a brief motionless stare. An absence seizure typically lasts several seconds, but may last up to 30 seconds. Speech is interrupted momentarily, and the subject will then resume speaking. The attack may be influenced by sensory input, and may terminate when the individual is spoken to. Absence seizures occur in...

Stereotactic Radiosurgery

Surgeons use energy in many forms to cure disease. Scalpels, lasers, and electrocautery were the initial tools of the neurosurgeon. Recent advances in neuroimaging, computer science, and stereotactic dose planning allow neurosurgeons to use sculpted radiation fields to alter the biology of disease. Stereotactic radiosurgery is the mechanically precise delivery of a potentially cytostatic, obliterative, or functionally incapacitating single dose of radiation to an imaging-defined target volume...

Target Selection

The sites commonly selected for DBS include PVG, specific STh, and IC. The type of pain a patient presents with dictates the anatomical target selection. Nociceptive pain, which is usually diffuse, midline, deep, boring, and may be bilateral with one side being more painful than the other, responds best to PVG stimulation. Neuropathic pain, which is usually characterized as being localized, burning, and felt on the surface, often unilateral, is amenable to STh stimulation. Deafferentation pain...

Pulse Generator Implantation And Programming

Those patients achieving greater than 50 pain relief as compared to pre-surgical levels have their systems internalized under general anesthesia. Those patients who do not achieve this degree of pain control have their electrodes removed. The distal end of the deep brain electrode is connected to an implant-able and programmable pulse stimulator (Itrel II or III, Medtronic), which is placed in a subcutaneous pocket in the infraclavicular region. For this purpose, a connector cord has to be...

Intraoperative Localization

It is necessary to determine the location of a point in space to register the patient and image spaces. A variety of devices have been developed that communicate the location of some device (wand, microscope, surgical instrument, etc.) relative to the patient to a computer, which then translates that position into image space. The Zeiss MKM microscope (Zeiss Corporation, Jena, Germany) combines a robotic arm mechanism and an optical microscope. The Neuronavigator (ISG Technologies, Toronto,...

Post Treatment

Once treatment is concluded, the headring is removed. The patient is advised to use ice packs to the anterior pin sites two times per day for the ensuing 48 hours. As the area postrema would have received a small dose during the treatment, a precautionary standard dose of dexamethasone 4 mg is given to all patients. With this, there has been no significant nausea or vomiting after the procedure. All patients other than those who are having a GA for the procedure are treated as outpatients and...

Partial Seizures

When onset is focal, seizures are referred to as partial seizures, but the term focal is still used. Partial seizures occur when electrical activation begins in a localized region of one cerebral hemisphere. Partial seizures are classified primarily on the basis of whether consciousness is altered. When consciousness is preserved, seizures are referred to as simple partial seizures. When consciousness is altered or impaired, seizures are classified as complex partial seizures. If the electrical...

Reported Efficacy Of Avm Radiosurgery

Many series have evaluated rates of AVM thrombosis after radiosurgery 10,14-29 . Overall reported rates of successful angiographic AVM obliteration range from 56 to 92 (Table 1). The rate of obliteration is strongly correlated with AVM size. For example, among the 153 AVM radiosurgery patients who have undergone 3-year follow-up angiography at the University Figure 2 Treatment plan, contrast-enhanced computed tomography (CT). This 43-year-old male presented with seizures and refused surgical...

Selective Radiofrequency Rhizotomy

Radiofrequency trigeminal rhizotomy depends on a differential vulnerability of pain and touch fibers to thermocoagulation. The A-delta and C fibers that relay pain are more susceptible to injury than the A-alpha and beta fibers that carry touch sensation. There are two electrode types. Either a thin cordotomy-type electrode or a larger, curved electrode with temperature monitoring capabilities are available 10,11 . Thermistor controlled radio-frequency lesion generators are available from...

Tonic Clonic Seizures

This is the most commonly encountered generalized seizure and is also referred to as a grand mal seizure or convulsion. Generalized seizures may occur in either childhood or adult life, and are often preceded by a flurry of myoclonic seizures. Typically, no warning precedes the seizure, although patients may complain of vague premonitions (examples include nervousness or irritability) minutes to hours before the seizure. Abrupt tonic contractions of muscles result in the patient falling to the...

Structure Contouring Tools

Contours of objects are drawn in the two-dimensional axial CT or MR images displayed in the main window, whereas coronal and sagittal reconstructions of the objects are simultaneously displayed in the smaller windows below. Each completed object (defined in CT or MRI) is transferred to the three-dimensional database. The target is defined on both CT and MRI. The main drawing tool takes advantage of the three mouse buttons and consists of a circular cursor that can be used as a brush either for...