Early postoperative appearance of radiofrequency lesions on magnetic resonance imaging

Convection-Enhanced Delivery of Muscimol Into the Bilateral Subthalamic Nuclei of Nonhuman Primates

BACKGROUND

Muscimol is a gamma-aminobutyric acid receptor agonist that selectively and temporarily inhibits neurons. Local bolus injection of muscimol has been used experimentally to inhibit neuronal populations within discrete anatomical structures and discern their physiological function.

OBJECTIVE

To determine the safety and behavioral effects of convection-enhanced delivery of muscimol into the bilateral subthalamic nuclei (STN) of nonhuman primate rhesus macaques (NHPs).

METHODS

Six awake NHPs underwent co-infusion of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA), a surrogate magnetic resonance imaging (MRI) tracer, with increasing concentrations of muscimol for behavioral and histological assessment. Three other NHPs were co-infused with Gd-DTPA and 3H-muscimol into the STN to determine muscimol distribution by MRI and autoradiography. Two NHPs underwent microcatheter implantation without muscimol infusion for control comparison.

RESULTS

MRI revealed selective and complete perfusion of the bilateral STN in animals infused with Gd-DTPA and muscimol. No abnormal movements occurred at 0.125 mM. Muscimol doses between 0.25 and 4.4 mM resulted in transient, dose-dependent hyperkinesia. Muscimol (8.8 mM) resulted in severe bilateral dyskinesias, ballistic movements, and sedation. An 88.8 mM dose produced unresponsiveness in 1 animal. Infusion-related pathological abnormities or toxicity was not present on histological examination. MRI distribution of co-infused Gd-DTPA was similar to autoradiographic distribution of 3H-muscimol (Vd; R = 0.94). Mean Vd of infused animals was 37.9 mm3 ± 11.7 mm3 and mean Vd: Vi 7.6 ± 2.3.

CONCLUSION

Bilateral convection-enhanced delivery of muscimol into the primate STN resulted in dose-related hyperkinetic movements that resolved after stopping the infusion. Muscimol was not toxic to brain tissue. Gd-DTPA accurately tracked muscimol distribution.

Postoperative MRI Evaluation of a Radiofrequency Cordotomy Lesion for Intractable Cancer Pain

BACKGROUND AND PURPOSE

There are limited data on the use of postoperative imaging to evaluate the cordotomy lesion. We aimed to describe the cordotomy lesion by using postoperative MR imaging in patients after percutaneous cordotomy for intractable cancer pain.

MATERIALS AND METHODS

Postoperative MR imaging and clinical outcomes were prospectively obtained for 10 patients after percutaneous cordotomy for intractable cancer pain. Area, signal intensity, and location of the lesion were recorded. Clinical outcomes were measured by using the Visual Analog Scale and the Brief Pain Inventory-Short Form, and correlations with MR imaging metrics were evaluated.

RESULTS

Ten patients (5 men, 5 women; mean age, 58.5 ± 9.6 years) were included in this study. The cordotomy lesion was hyperintense with central hypointense foci on T2-weighted MR imaging, and it was centered in the anterolateral quadrant at the C1-C2 level. The mean percentage of total cord area lesioned was 24.9% ± 7.9%, and most lesions were centered in the dorsolateral region of the anterolateral quadrant (66% of the anterolateral quadrant). The number of pial penetrations correlated with the percentage of total cord area that was lesioned (r = 0.78; 95% CI, 0.44-0.89; P = .008) and the length of T2-weighted hyperintensity (r = 0.85; 95% CI, 0.54-0.89; P = .002). No significant correlations were found between early clinical outcomes and quantitative MR imaging metrics.

CONCLUSIONS

We describe qualitative and quantitative characteristics of a cordotomy lesion on early postoperative MR imaging. The size and length of the lesion on MR imaging correlate with the number of pial penetrations. Larger studies are needed to further investigate the clinical correlates of MR imaging metrics after percutaneous cordotomy.

Early MRI Characteristics after MRI-Guided Laser-Assisted Cingulotomy for Intractable Pain Control

BACKGROUND AND PURPOSE

Cingulotomy is a well-accepted stereotactic procedure in the treatment of debilitating pain syndromes. At our institution, we used a 980-nm diode laser to perform MR imaging-guided laser-assisted cingulotomy. We report the early MR imaging changes associated with this technique.

MATERIALS AND METHODS

In this retrospective analysis, MR imaging-guided laser-assisted cingulotomy was performed in 4 patients with intractable pain secondary to metastatic disease. Patients were imaged at various time points postprocedure, with visual analysis of MR imaging changes in the cingulate gyri during that timeframe.

RESULTS

Twenty-four hours postablation, 4 distinct zones of concentric rings reminiscent of an "owl eye" shape were noted in the cingulate gyri. Extrapolating from the imaging characteristics of the rings, we defined each zone as follows: The central zone (zone 1) represents a laser probe void with fluid, zones 2 and 3 have signal characteristics that represent hemorrhage and leaked protein, and zone 4 has a peripheral ring of acute infarction, enhancement, and surrounding edema. One patient with 1-year follow-up showed persistent concentric rings with resolution of enhancement and edema.

CONCLUSIONS

Post-MR imaging-guided laser-assisted cingulotomy rings appear to represent a continuum of injury created by the laser probe and thermal injury. The imaging changes are similar to those described for laser ablation of tumor-infiltrated brain with a 1064-nm laser. This is the first study to characterize early MR imaging changes after MR imaging-guided laser-assisted cingulotomy by using a 980-nm laser. It is important for neuroradiologists and neurosurgeons to understand expected imaging findings as laser ablation cingulotomy re-emerges to treat intractable pain.

Postoperative MRI examinations in patients treated by deep brain stimulation using a non-standard protocol

BACKGROUND

MRI in patients bearing deep brain stimulation (DBS) electrodes may induce cerebral lesions due to electrode heating. To avoid neurological deficits related to MRI, post-operative MRI protocol was installed in our institution. However, our protocol comprised a higher specific absorption rate (SAR) and different positioning of lead excess than the later released electrode manufacturer's guidelines. The objective was to evaluate the safety using this protocol.

METHODS

Between January 2000 and May 2008, post-operative MRI was performed in all patients. In selected patients, additional MRI scans were performed with the implanted generator. MRI was acquired at 1.5 T with a RF transmit/receive head coil comprising a T2-weighted fast spin echo (FSE) and a T1-weighted inversion recovery FSE sequence. Local cranial SAR values measured up to 0.9 W/kg compared to the manufacturer's recommendation of 0.1 W/kg. Initial scans (1-7 days after surgery) were performed with externalized leads, long-term scans (>30 days after surgery) with a connected generator. New neurological deficits were assessed before and after MRI. Additional MRIs were compared to the initial postoperative MRI with emphasis on new lesions.

RESULTS

In 211 patients, 243 MRIs were performed, including 212 initial post-operative MRI. In 12% (n = 24), 31 additional MRI examinations for various clinical reasons were achieved. No patients demonstrated new neurological deficits during or after MRI acquisitions.

CONCLUSIONS

No complications were observed using this MRI protocol in DBS patients. Our results suggest that, within this setting, higher SAR values may be feasible for DBS patients than in the manufacturer's guidelines.

Radiological airway changes following bipolar radiofrequency volumetric tissue reduction

Objective:

To characterise the appearance of lesions of the tongue base and soft palate induced by bipolar radiofrequency volumetric tissue reduction, using magnetic resonance imaging up to six weeks post-procedure.

Methods:

Five men with sleep-disordered breathing were treated with one session of bipolar radiofrequency volumetric tissue reduction to a number of sites, including the tongue base and soft palate. Magnetic resonance imaging was performed pre-operatively and one week and six weeks after surgery.

Results:

Lesions were visible from day one. T1 (spine lattice relaxation Time)-weighted images demonstrated areas of central hyperintensity, reflecting haemorrhagic, coagulative necrosis, surrounded by hypointensity, representing oedema; corresponding short tau inversion recovery (STIR) sequences showed central hypointensity with surrounding high signal. The lesions expanded up to day three and then gradually diminished, but were still evident at week six on short tau inversion recovery images.

Conclusion:

The characterisation of lesions induced by bipolar radiofrequency volumetric tissue reduction enables us to elucidate the pathophysiology of this procedure, to optimise treatment benefits and clinical outcomes, and to explain patient symptoms.

Inter-racial, gender and aging influences in the length of anterior commissure-posterior commissure line

OBJECTIVE

The length of anterior-posterior commissure (AC-PC) in racial groups, age, gender of patients with deep brain stimulation (DBS) and pallidotomy were investigated.

METHODS

From January 1996 to December 2003, 211 patients were treated with DBS and pallidotomy. There were 160 (76%) Caucasians, 35 (17%) Hispanics, 12 (5%) Asians and 4 Blacks (2%). There were 88 males and 52 females in DBS-surgery group and 44 males, 27 females in pallidotomy group. Mean age was 58 year-old. There were 19 males and 19 females and mean age was 54.7 years in the control group. Measurements were made on MRI and @Target software.

RESULTS

The average AC-PC distance was 24.89 mm (range 32 to 19), which increased with aging until 75 years old in Caucasian and also increased with aging in Hispanic, but the AC-PC distance peaked at 45 years old in Hispanic. The order of AC-PC distance were 25.2+/-2 mm in Caucasian, 24.6+/-2.24 mm in Asian, 24.53 mm in Black, 23.6+/-1.98 mm in Hispanic. The average AC-PC distance in all groups was 24.22 mm in female who was mean age of 56.35, 25.28 mm in male who was mean age of 60.19 and 24.5+/-2 mm in control group that was excluded because of the difference of thickness of slice. According to multiple regression analysis, the AC-PC distance was significantly correlated with age, race, and gender.

CONCLUSION

The AC-PC distance is significantly correlated with age, gender, and race. The atlas of functional stereotaxis would be depended on the variation of indivisual brain that can influenced by aging, gender, and race.

Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity: modelling, simulation and analysis of parameter influence and interaction

Radio-frequency brain lesioning is a method for reducing e.g. symptoms of movement disorders. A small electrode is used to thermally coagulate malfunctioning tissue. Influence on lesion size from thermal and electric conductivity of the tissue, microvascular perfusion and preset electrode temperature was investigated using a finite-element model. Perfusion was modelled as an increased thermal conductivity in non-coagulated tissue. The parameters were analysed using a 2(4)-factorial design (n=16) and quadratic regression analysis (n=47). Increased thermal conductivity of the tissue increased lesion volume, while increased perfusion decreased it since coagulation creates a thermally insulating layer due to the cessation of blood perfusion. These effects were strengthened with increased preset temperature. The electric conductivity had negligible effect. Simulations were found realistic compared to in vivo experimental lesions.

Local distribution and toxicity of prolonged hippocampal infusion of muscimol

OBJECT

The activity of gamma-aminobutyric acid (GABA), the principal inhibitory neurotransmitter, is reduced in the hippocampus in patients with complex partial seizures from mesial temporal sclerosis. To provide preliminary safety and distribution data on using convection-enhanced delivery of agents to treat complex partial seizures and to test the efficacy and safety of regional selective neuronal suppression, the authors infused muscimol, a GABA-A receptor agonist, directly into the hippocampus of nonhuman primates using an integrated catheter electrode.

METHODS

Ten rhesus monkeys were divided into three groups: 1) use of catheter electrode alone (four monkeys); 2) infusion of escalating concentrations of muscimol followed by vehicle (three monkeys); and 3) infusion of vehicle and subsequent muscimol mixed with muscimol tracer (three monkeys). Infusions were begun 5 days after catheter electrode placement and continued for 5.6 days before switching to the other agent. Head magnetic resonance (MR) images and electroencephalography recordings were obtained before and during the infusions. Brain histological studies and quantitative autoradiography were performed. Neurological function was normal in controls and when muscimol concentrations were 0.125 mM or less, whereas higher concentrations (0.5 and 1 mM) produced reversible apathy and somnolence. Fluid distribution was demonstrated on MR images and muscimol distribution was demonstrated on autoradiographs throughout the hippocampus and adjacent white matter.

CONCLUSIONS

Targeted modulation of neuronal activity is a reasonable research strategy for the investigation and treatment of medically intractable epilepsy.

Incidence of hemorrhage associated with electrophysiological studies performed using macroelectrodes and microelectrodes in functional neurosurgery

Object. The goal of this study was to analyze the incidence of intracranial bleeding in patients who underwent procedures guided by microelectrode recording (MER) rather than by macroelectrode stimulation alone.

Methods. Between March 1994 and July 2001, 178 patients underwent 248 functional neurosurgical procedures performed by the same team at the University of California at Los Angeles. The procedures included pallidotomy (122 patients), thalamotomy (19 patients), and implantation of deep brain stimulation electrodes in the subthalamic nucleus (36 patients), globus pallidus internus (17 patients), and ventralis intermedius nucleus (54 patients). One hundred forty-four procedures involved macroelectrode stimulation and 104 involved MER. Groups were analyzed according to the presence of arterial hypertension, MER or macroelectrode stimulation use, and occurrence of hemorrhage. Nineteen patients with arterial hypertension underwent 28 surgical procedures.

Five cases of hemorrhage (2.02%) occurred. One patient presented with hemiparesis and dysphasia but no surgery was required. The incidence of hemorrhage in patients in whom MER was performed was 2.9%, whereas the incidence in patients in whom MER was not used was 1.4% (p = 0.6529). Bleeding occurred in 10.71% of patients with hypertension and 0.91% of those who were nonhypertensive (p = 0.0111). Among the 104 patients in whom MER was performed, 12 had hypertension. Bleeding occurred in two (16.67%) of these 12 patients. An increased incidence of bleeding in hypertensive patients who underwent MER (p = 0.034) was noticed when compared with nonhypertensive patients who underwent MER. A higher number of electrode passes through the parenchyma was observed when MER was used (p = 0.0001). A positive trend between the occurrence of hemorrhage and multiple passes was noticed.

Conclusions. Based on the data the authors suggest that a higher incidence of hemorrhage occurs in hypertensive patients, and a higher incidence as well in hypertensive patients who underwent MER rather than macroeletrode stimulation. Special attention should be given to MER use in hypertensive patients and particular attention should be made to multiple passes.

SEEG-guided RF Thermocoagulation of Epileptic Foci: Feasibility, Safety, and Preliminary Results

PURPOSE

Depth electrodes recordings may be required in some cases of epilepsy surgery to delineate the best region for cortical resection. We usually implant depth electrodes according to Talairach's stereoelectroencephalography (SEEG) method. By using these permanently implanted depth electrodes, we are able to perform radiofrequency (RF)-thermolesions of the epileptic foci. We report the technical data required to perform such multiple cortical thermolesions, as well as preliminary results in terms of seizure outcome in a group of 20 patients.

METHODS

Lesions were performed by using 100- to 110-mA bipolar current (50 V), applied for 10 to 50 s. Each thermocoagulation produced a 5- to 7-mm diameter cortical lesion. In total, two to 16 lesions were performed in each of the 20 patients. Lesions were placed without anesthesia. No general or neurologic complication occurred during the procedures. Two transient postprocedure side effects, consisting of paresthetic sensations in the mouth and mild apraxia of the hand, were observed.

RESULTS

At a follow-up time of 8 to 31 months (mean, 19 months), 15% of the patients became seizure free, 40% experienced a > or =80% reduction of their seizure frequency, and 45% were not significantly improved.

CONCLUSIONS

SEEG-guided RF thermolesions is a safe technique. Our preliminary results indicate that such lesions can lead to a significant reduction of seizure frequency and could be proposed as a palliative procedure if no resective surgery is possible. A randomized controlled trial is needed to determine which patients are likely to respond to SEEG-guided RF thermolesions.

Percutaneous MR Imaging– guided Radiofrequency Interstitial Thermal Ablation of Tongue Base in Porcine Models: Implications for Obstructive Sleep Apnea Syndrome

PURPOSE

To test the feasibility and safety of a percutaneous magnetic resonance (MR) imaging-guided technique for radiofrequency (RF) interstitial thermal ablation of the tongue base and to correlate MR appearance of induced thermal lesions with histopathologic findings in pigs in acute and chronic porcine models.

MATERIALS AND METHODS

A 1-cm-tip RF electrode was inserted percutaneously into the tongue in 10 pigs with 0.2-T real-time MR guidance. The RF electrode was advanced up the midline between lingual arteries and stopped short of tongue mucosa. RF interstitial thermal ablation was performed at 90 degrees C +/- 2 and lasted 10 minutes. Postablation images were obtained with a 1.5-T MR imager. Five pigs were sacrificed immediately (acute model), while five were followed up for 1 month (chronic model) before they were sacrificed. MR-compatible fiducial coils were inserted into tongues with MR imaging guidance prior to RF ablation in the chronic group. Tongues were harvested for histopathologic analysis. Mean thermal lesion volume was compared with the Student t test on images obtained immediately, 2 weeks, and 1 month after RF ablation. Interclass correlation coefficients of lesion diameters at gross pathologic analysis and corresponding diameters with each pulse sequence were calculated.

RESULTS

Successful MR imaging-guided electrode positioning was achieved in all procedures without intra- or postprocedure complications because there was high vascular conspicuity and tissue contrast. Thermal lesions appeared hypointense with hyperintense surrounding rims with all sequences in both groups. At pathologic analysis, acute lesions appeared as pale necrotic areas surrounded by hyperemic rims, while chronic lesions demonstrated progressive circumferential fibrosis and significant volume shrinkage (P <.01). Thermal lesion diameters measured at gross pathologic analysis best agreed with corresponding diameters measured on short inversion time inversion-recovery images (interclass correlation coefficient = 0.85).

CONCLUSION

The results of this investigation demonstrate MR imaging-guided RF interstitial thermal ablation of the tongue base is feasible and safe and illustrate imaging and pathologic phenomena associated with creation and evolution of the induced thermal lesions.

[Magnetic resonance imaging in the evaluation of temperature-controlled radiofrequency volumetric tissue reduction]

BACKGROUND

Due to its minimally invasive character, radiofrequency surgery has become a topic of increasing attention, especially with respect to the surgical treatment of sleep-related breathing disorders. Temperature-controlled radiofrequency volumetric tissue reduction is the most common technique employed in these cases. However, despite the increasingly widespread use of this technique, there is little data available on the induced effects in vivo. The aim of the present study was to investigate whether magnetic resonance imaging could be used in the evaluation of the in vivo effects of radiofrequency surgery at the base of the tongue.

PATIENTS AND METHODS

Six patients were treated at the base of tongue with radiofrequency surgery. At 4-6, 8-10 and 24 h after surgery, magnetic resonance imaging was performed using an inversion recovery technique (TIRM) and the lesions created were evaluated.

RESULTS

The lesions could be visualised at all postoperative measurement times. They appeared as oval hypointense structures encircled by a hyperintense area. Lesion size diminished slightly over time.

DISCUSSION

Lesions induced by radiofrequency surgery can be clearly visualised with magnetic resonance imaging. Lesion size may be assessed in relation to energy application. In the future, the treatment of sleep-related breathing disorders may be further optimised with the help of this technique.

Lesion formation in radiofrequency surgery of the tongue base

OBJECTIVES

Temperature controlled radiofrequency volumetric tissue reduction (RFVTR) of the tongue base is a minimally invasive technique for the treatment of obstructive sleep apnea. But despite its widespread use, little is yet known about in vivo effects in humans. Such knowledge would be essential for evidence-based criteria in the selection of energy application.

METHODS

In a preparatory in vitro study, porcine tongues were preserved in growing medium. Lesions with different amounts of energy were applied, and maximum diameters were assessed. In the in vivo study, 11 patients were treated with RFVTR at the tongue base by employing different energy levels (800, 600, 400, or 200 J) on two application sites. Magnetic resonance imagery scans were performed 4 to 6, 8 to 10, and 24 hours after surgery. An inversion recovery technique was used to visualize the lesions.

RESULTS

RFVTR created lesions at the porcine tongue from 50 J and higher. Maximum lesion sizes were achieved with 400 J. In vivo, all the lesions were clearly visible in the postoperative scans. Lesion size increased with the amount of energy applied. Maximum diameters were created from 600 J and higher. Higher amounts of energy only resulted in a slight increase in lesion length.

CONCLUSIONS

The application of 600 J at 85 degrees C leads to optimal lesion sizes. Higher amounts of energy will not lead to a relevant increase in tissue necrosis. With regard to the time needed for application, 600 J appears to be the ideal adjustment for energy delivery in the treatment of the human tongue.

MR imaging-guided radio-frequency thermal ablation of the lumbar vertebrae in porcine models

PURPOSE

To test the hypotheses that (a) magnetic resonance (MR) imaging-guided radio-frequency (RF) thermal ablation of the vertebrae is feasible in porcine models, (b) procedure safety depends on the location of ablation within the vertebra, and (c) MR imaging allows accurate monitoring of induced thermal lesion size and shape.

MATERIALS AND METHODS

Ten percutaneous MR imaging-guided RF thermal ablations were randomized over various lumbar vertebral levels and locations in seven pigs. Animals were followed up for 2, 7, or 14 days before sacrifice. Thermal lesion size and shape as measured on MR images obtained immediately after ablation and at follow-up were compared with gross pathologic findings. Mean absolute differences between lesion diameters at pathologic examination and MR imaging were evaluated by using a paired t test, as were differences between lesion-to-vertebra contrast-to-noise ratios obtained for each sequence. Clinical and imaging data were correlated with histologic findings.

RESULTS

Successful RF electrode placement in the targeted part of the vertebra was achieved in all procedures. Ablations performed away from neural elements were safe to perform. Pedicular ablations resulted in radiculopathy, whereas ablations performed directly over the posterior cortex resulted in paraplegia. Lesion sizes measured on T2-weighted images were closest to those measured at gross pathologic examination (mean absolute difference, 0.72 mm +/- 0.83 [SD]), followed by those measured on contrast material-enhanced T1-weighted (1.27 mm +/- 0.83) and short inversion time inversion-recovery (STIR) (1.5 mm +/- 1.84) images. Size measurements obtained on T2-weighted images were significantly closer to gross pathologic measurements than were those obtained on contrast-enhanced T1-weighted images (P =.013) but were not different from those obtained on STIR (P =.27) images. The contrast-to-noise ratio was significantly higher for contrast-enhanced T1-weighted images than for T2-weighted (P <.001) or STIR (P <.001) images.

CONCLUSION

MR imaging-guided RF thermal ablation of the vertebrae is feasible in porcine models, but the safety of the procedure depends on the location of ablation within the vertebra. MR imaging allows accurate monitoring of thermal lesion size and shape.

Optimal location of thalamotomy lesions for tremor associated with Parkinson disease: a probabilistic analysis based on postoperative magnetic resonance imaging and an integrated digital atlas

OBJECT

Renewed interest in stereotactic neurosurgery for movement disorders has led to numerous reports of clinical outcomes associated with different treatment strategies. Nevertheless, there is a paucity of autopsy and imaging data that can be used to describe the optimal size and location of lesions or the location of implantable stimulators. In this study the authors correlated the clinical efficacy of stereotactic thalamotomy for tremor with precise anatomical localization by using postoperative magnetic resonance (MR) imaging and an integrated deformable digital atlas of subcortical structures.

METHODS

Thirty-one lesions were created by stereotactic thalamotomy in 25 patients with tremor-dominant Parkinson disease. Lesion volume and configuration were evaluated by reviewing early postoperative MR images and were correlated with excellent, good, or fair tremor outcome categories. To allow valid comparisons of configurations of lesions with respect to cytoarchitectonic thalamic boundaries, the MR image obtained in each patient was nonlinearly deformed into a standardized MR imaging space, which included an integrated atlas of the basal ganglia and thalamus. The volume and precise location of lesions associated with different clinical outcomes were compared using nonparametric statistical methods. Probabilistic maps of lesions in each tremor outcome category were generated and compared. Statistically significant differences in lesion location between excellent and good. and excellent and fair outcome categories were demonstrated. On average, lesions associated with excellent outcomes involved thalamic areas located more posteriorly than sites affected by lesions in the other two outcome groups. Subtraction analysis revealed that lesions correlated with excellent outcomes necessarily involved the interface of the nucleus ventralis intermedius (Vim; also known as the ventral lateral posterior nucleus [VLp]) and the nucleus ventrocaudalis (Vc; also known as the ventral posterior [VP] nucleus). Differences in lesion volume among outcome groups did not achieve statistical significance.

CONCLUSIONS

Anatomical evaluation of lesions within a standardized MR image-atlas integrated reference space is a useful method for determining optimal lesion localization. The results of an analysis of probabilistic maps indicates that optimal relief of tremor is associated with lesions involving the Vim (VLp) and the anterior Vc (VP).

Pallidotomy microelectrode targeting: neurophysiology-based target refinement

OBJECTIVE

Microelectrode recording can refine targeting for stereotactic radiofrequency lesioning of the globus pallidus to treat Parkinson's disease. Multiple intraoperative microelectrode recording/stimulating tracks are searched and assessed for neuronal activity, presence of tremor cells, visual responses, and responses to kinesthetic input. These physiological data are then correlated with atlas-based anatomic data to approximate electrode location. On the basis of these physiological properties, one or more tracks are selected for lesioning. This study analyzes the track physiological factors that seem most significant in determining the microelectrode recording track(s) that will be chosen for pallidal lesioning.

METHODS

Thirty-six patients with Parkinson's disease underwent microelectrode-guided pallidotomy. Between one and five microelectrode recording tracks were made per patient. Usually, one (n = 23) or two (n = 12) of these tracks were lesioned. Electrode positions in the x (mediolateral) and y (anteroposterior) axes were recorded and related to track neurophysiological findings and final lesion location. The stereotactic location and sequence of microelectrode tracks were recorded and plotted to illustrate individual search patterns. These patterns were then compared with those noted in other patients. Neurophysiological data obtained from recording tracks were analyzed. A retrospective analysis of track electrophysiology was performed to determine the track characteristics that seemed most important in the surgeon's choice of the track to lesion. Track physiological properties included general cell spike amplitude, tremor synchronous neuronal firing, kinesthetically responsive neuronal firing, and optic track responses (either phosphenes reported by the patient during track microstimulation or neuronal firing in response to light stimulus into the patient's eyes). Orthogonally corrected postoperative magnetic resonance images were used to confirm the anatomic lesion locations.

RESULTS

In patients who had a single mapped track lesioned, specific track electrophysiological characteristics identified the track that would be lesioned most of the time (20 of 24 patients). Tracks that exhibited a combination of tremor synchronous firing, joint kinesthesia, and visual responsivity were lesioned 17 (85%) of 20 times. Analysis of intraoperative electrode movement in the x and y axes indicated a significant subset of moves but did not result in microelectrode positioning closer to the subsequently lesioned track. Accuracy of initial electrode movement in the x and y axes was most highly correlated with a measure of first-track electrophysiological activity. The number of microelectrode recording tracks did not correlate with clinical outcome. Anatomic analysis, using postoperative magnetic resonance imaging, revealed that all lesions were placed in the globus pallidus. Most patients (35 of 36) improved after surgery.

CONCLUSION

The level of electrophysiological activity in the first track was the best predictive factor in determining whether the next microelectrode move would be closer to the ultimately lesioned track. The analysis of electrode track location and neurophysiological properties yields useful information regarding the effectiveness of microelectrode searching in the x and y axes. Within an institution, the application of this modeling method may increase the efficiency of the microelectrode refinement process.

MR imaging-guided radio-frequency thermal ablation in the pancreas in a porcine model with a modified clinical C-arm system

PURPOSE

To test the hypotheses that (a) magnetic resonance (MR) imaging-guided radio-frequency (RF) thermal ablation in the pancreas is safe and feasible in a porcine model and (b) induced thermal lesion size can be predicted with MR imaging monitoring.

MATERIALS AND METHODS

MR imaging-guided RF ablation was performed in the pancreas of six pigs. A 17-gauge monopolar RF probe was inserted into the pancreas with MR imaging guidance, and RF was applied for 10 minutes. After postprocedural imaging (T2-weighted, short inversion time inversion-recovery [STIR], and T1-weighted imaging before and after intravenous administration of gadodiamide), the pigs were observed for 7 days and follow-up MR images were acquired. The pigs were sacrificed, and pathologic examination was performed.

RESULTS

Successful RF probe placement was accomplished in all pigs; the interventional procedure took 46-80 minutes. Thermal lesions were 12-15 mm perpendicular to the probe track and were best seen on STIR and contrast material-enhanced T1-weighted images with a radiologic and/or pathologic mean difference in RF lesion diameter of 1.7 mm +/- 1.0 (SD) and 0.8 mm +/- 1.2, respectively. Diarrhea was the only side effect during the 1-week follow-up; no clinical signs of pancreatitis occurred.

CONCLUSION

MR imaging-guided RF thermal ablation in the pancreas is feasible and safe. Induced thermal lesion size can best be monitored with STIR and contrast-enhanced T1-weighted images. In the future, RF ablation may offer an alternative treatment option for pancreatic cancer.

Stereotactic amygdalohippocampotomy for the treatment of medial temporal lobe epilepsy

PURPOSE

This study was carried out to assess the safety and efficacy of stereotactic ablation of the amygdala and hippocampus for the treatment of medial temporal lobe epilepsy.

METHODS

Twenty-two stereotactic amygdalohippocampotomies were performed in 19 patients with unilateral temporal lobe seizures by using magnetic resonance imaging (MRI) localization for target planning and radiofrequency techniques for lesion production. Seizure frequency was assessed at 3-monthly follow-up visits. Two lesion groups were defined. In group I, four to 11 (mean, 6.4) discrete lesions were made, encompassing the amygdala and anterior 13-21 mm (mean, 16.8 mm) of the hippocampus. In group II, a large number of confluent lesions were made (mean, 26.0; range, 12-54) encompassing the amygdala and anterior 15-34 mm (mean, 21.5 mm) of the hippocampus. MRI scanning was carried out 24 h and 6-9 months after surgery.

RESULTS

In five group I patients, one (20%) experienced a favorable seizure outcome. Of 15 group II patients, one of whom had previously undergone limited lesioning and was also analyzed as part of group I, nine (60%) experienced a favorable seizure outcome, with two seizure free. MRI scans at 6- to 9-months' follow-up disclosed discrete areas of atrophy in the amygdala and hippocampus, interspersed with preserved brain in the group I patients. More uniform and complete destruction of amygdala and hippocampus was evident in group II patients. All lesions were confined to the amygdala and hippocampus, sparing the parahippocampal gyrus (PHG).

CONCLUSIONS

The extensive amygdalohippocampal ablation in group II patients improved seizure outcome compared with more limited ablation in group I, but these results were not so good as those from temporal lobectomy in a similar patient group. When considered together with the results of selective amygdalohippocampectomy, and temporal resections that spare hippocampus or amygdala (all producing similar outcomes, and all involving resection of the entorhinal cortex), this study suggests a pivotal role of the entorhinal cortex in temporal epileptogenesis.

Variability in lesion location after microelectrode-guided pallidotomy for Parkinson's disease: anatomical, physiological, and technical factors that determine lesion distribution

OBJECT

To understand the factors that determine the distribution of lesions after microelectrode-guided pallidotomy for Parkinson's disease, the authors quantitatively characterized lesion location in a cohort of patients who were prospectively followed to determine the effects of pallidotomy on clinical outcome.

METHODS

Thirty-three patients underwent volumetric magnetic resonance (MR) imaging after surgery to allow quantitative lesion localization in relation to conventional intraventricular landmarks and, alternatively, more anatomically relevant landmarks. The validity of the method was verified in a cohort of postpallidotomy patients who underwent concurrent volumetric and stereotactic MR imaging in an external head frame. Lesions were distributed over a considerable distance in the anteroposterior (8.8 mm) and mediolateral (8.7 mm) dimensions in relation to the anterior commissure and wall of the third ventricle, respectively. Less variation was seen in lesion location in the dorsoventral dimension (4.8 mm) in relation to the intercommissural plane.

CONCLUSIONS

Lesion distribution was not random: lesion locations in the anteroposterior and mediolateral dimensions were highly correlated, such that lesions were distributed from anteromedial to posterolateral, parallel to the border of the globus pallidus internus with the obliquely oriented internal capsule. The factors that led to variability in lesion location were variation in third ventricle width and the oblique anteromedial-to-posterolateral course of the internal capsule. This demonstration of variability of lesion location in a cohort of patients who experienced excellent clinical benefits and minimal postoperative complications emphasizes the importance of anatomical variations in determining lesion position and the need for physiological corroboration for correct lesion placement.

MRI monitoring of interstitial microwave-induced heating and thermal lesions in rabbit brain in vivo

The purpose of this experiment was to use MRI to monitor microwave heating and thermal damage of brain tissue in vivo. Interstitial microwave antennas were implanted into the cerebral hemispheres of seven anesthetized rabbits. Variable power of 30 to 100 W was applied for periods of 5 to 15 minutes and tissue temperature was monitored continuously. MR images were obtained throughout the procedure at 20-second intervals, using a spoiled gradient-echo sequence, without significant artifact. Magnitude, phase, and complex difference images all demonstrated temperature-related signal changes during heating. The findings were better visualized on the phase and complex difference images. Phase difference image analysis revealed an approximately linear relationship between phase change and temperature. Post-treatment thermal lesions measured up to 2.0 cm in size on pathologic specimens and exhibited a zonal pattern on spin-echo MR images.

Delayed internal capsule infarctions following radiofrequency pallidotomy. Report of three cases

The authors report on a series of patients with idiopathic Parkinson's disease (IPD) who underwent stereotactic radiofrequency (RF) pallidotomies, three of whom suffered delayed postoperative strokes. These three belonged to a group consisting of 42 patients with medically intractable IPD in whom 50 pallidotomies were performed. All three patients had significant previous vascular disease and were in a high-risk group for cerebral infarction. A postoperative magnetic resonance (MR) image was obtained immediately after the pallidotomy was performed to document the placement of the RF lesion and to rule out any hematoma. The delayed strokes occurred on postoperative Days 10, 51, and 117 in patients with previous vascular disease (Group 1, 11 patients). No strokes occurred in the group with the vascular disease risk factor (Group 2, 11 patients) or in the group with no risk factors for vascular disease (Group 3, 20 patients). This observation is statistically significant (p < 0.05). The T2-weighted MR images showed the lesions as high-intensity signals extending to the posterior limb of the internal capsule ipsilateral to the pallidotomy site. The poststroke T1-weighted images obtained in two patients showed persistent contrast enhancement of the RF lesion and no enhancement around the stroke lesion. Clinically and radiographically, these discrete new lesions represent delayed infarctions, suggesting that RF lesioning can induce delayed injury in adjacent tissue. Patients with previously identified vasculopathy may be at risk for delayed capsular infarction following RF pallidotomy.

Analysis of pallidotomy lesion positions using three-dimensional reconstruction of pallidal lesions, the basal ganglia, and the optic tract

OBJECTIVE

To assess the position of radiofrequency pallidotomy lesions placed using microelectrode stimulation and cellular recordings in relation to a stereotactically defined starting point. Radiofrequency lesion locations were also evaluated in relation to the putamen, posterior limb of the internal capsule, and optic tract.

METHODS

Magnetic resonance images obtained from 23 patients with Parkinson's disease who underwent pallidotomy at the University of Kansas Medical Center were analyzed. Using computerized techniques, lesion positions in relation to the midcommissural point and a hypothetical starting point were determined. Data segmentation and three-dimensional reconstruction of pallidal lesions, the internal capsule, and the optic tract allowed assessment of lesion position in relation to internal anatomy. Clinical outcome of pallidotomy was assessed using both the Unified Parkinson's Disease Rating Scale and the Dementia Rating Scale.

RESULTS

Pallidal lesions were usually placed anterior and dorsal to the stereotactically defined starting point. The position of pallidal lesions in the men were observed, in four trials, to be significantly more dorsal than the lesions in the women. The outer zone of the lesion was usually adjacent to the internal capsule and the putamen and relatively close to the optic tract. The inner zone of the lesion was usually several millimeters removed from anatomic boundaries of the putamen, internal capsule, and optic tract. Patients achieved favorable outcomes, with reduced dyskinesias and "off" time and improvement of their Parkinsonian symptoms, as evidenced by clinical assessment, the Unified Parkinson's Disease Rating Scale, and the Dementia Rating Scale.

CONCLUSION

Microelectrode stimulation and cellular recordings usually led to a final pallidotomy lesion position that deviated from the stereotactically defined starting point. The pallidotomy lesions in the men were observed to be more dorsal than the lesions in the women. Clinical outcomes were not correlated with either lesion location relative to the starting point or distances between the pallidal lesion and the putamen, internal capsule, or optic tract. Kinesthetically responsive cells may be localized generally more anterior and dorsal to the starting point (within the globus pallidus) and may be grouped variably from patient to patient in relation to other basal ganglia structures. Although the primary lesion site is most likely within the sensorimotor region of the globus pallidus internus, the more dorsal locations of responsive cell groups may indicate that some lesion sites may be localized within the globus pallidus externus.

Microelectrode-guided posteroventral pallidotomy for treatment of Parkinson's disease: postoperative magnetic resonance imaging analysis

The authors report the postoperative magnetic resonance (MR) imaging findings in 36 patients with advanced Parkinson's disease who underwent unilateral microelectrode-guided posteroventral pallidotomy. The lesions were placed within 1 mm of the ventral border of the globus pallidus internus (GPi) to include pallidothalamic outflow pathways. Sequential MR studies were obtained within 1 to 3 days postoperatively and at 6-month follow-up examination. Thirty-four (94%) of the 36 patients enjoyed sustained moderate or marked improvement of their parkinsonian symptoms 6 months postoperatively. Transient side effects occurred in five patients (14%), but there were no persistent complications. The pallidal radiofrequency lesions were prolate spheroid shaped and were composed of three concentric zones in the early postoperative studies. The mean volume of the middle zone, corresponding to the area of hemorrhagic coagulation necrosis, was 44.4 +/- 17.6 mm3; the mean lesion volume as defined by the outer zone, corresponding to perilesional edema, was 262.2 +/- 111.6 mm3. Additional edema spreading to the internal capsule was noted in 32 of 34 cases and to the optic tract in 11 of 34 cases. In two patients small ischemic infarctions involving the corona radiata were found, and in one a venous infarction was detected. Ischemic infarction resulted in mild transient Broca's aphasia in one patient, but there was no detectable neurological deficit in the other two. The mean volume of late-phase (6 months) lesions was 22 +/- 28.8 mm3. In three patients no lesion was identified despite sustained clinical improvement. The lesion was located in the posteroventral GPi in all cases except in one patient in whom it was confined to the GP externus (GPe). This 49-year-old woman did not experience sustained benefit. The authors found no consistent correlations between lesion size and location and clinical outcome as measured by a global outcome score, the Unified Parkinson's Disease Rating Scale motor, activities of daily living, and bradykinesia "off" scores or rating of dyskinesias. Lesioning of pallidal and subpallidal pathways may contribute to the sustained clinical benefit in this series. Magnetic resonance imaging analysis showed that intraoperative microelectrode recording facilitated accurate placement of the lesion in this critical area.

Identification and localization of intracerebral vessels by microvascular doppler in stereotactic pallidotomy and thalamotomy: technical note

OBJECTIVE

To identify intracerebral vessels in proximity to the target for thermocoagulation in functional neurosurgery, we use a microvascular doppler sensor held in a special supporting needle that fits in the straightening cannula for the thermocoagulation needle.

TECHNIQUE

After insertion of the straightening cannula aimed at the stereotactic target, the microvascular doppler probe positioned at the tip of a supporting hollow needle is advanced through the cannula. The proximal micrometer gauge indicates the depth of the tip of the doppler probe. By setting the doppler device to the shortest focusing depth (0.1 mm), the maximum pulsatile vascular sound indicates the depth of the vessel.

RESULTS AND CONCLUSION

A prominent vascular sound was identified in 3 of 13 cases. By adjusting the depth of the target, no major bleeding was experienced after thermocoagulation lesions were made. This technique secures and protects the fragile microvascular doppler and identifies any significant arterial vessels at the stereotactic target, thus avoiding vascular injury.

Controversies in pallidal surgery

Posteroventral pallidotomy (PVP) has gained a worldwide acceptance after its reintroduction by Laitinen et al. in 1992 (56) and many studies have since been published. A review of the recent literature reveals that there is variation in the clinical indications for this procedure, the surgical technique used and the assessment of results. There is no uniform practice in the choice of the anatomical target point within the globus pallidus, the imaging of the target structure, the intraoperative assessment of the physiological target and the mode of evaluation of the surgical results. Although some neurosurgeons advocate that the lesion should be in the lateral pallidum, the majority insist it should be in the medial pallidum. It is shown here that, as long as the lesion is made at the posterior and ventral parts of the globus pallidus, it will necessarily include aspects of both medial and lateral posteroventral pallidum. There is a common agreement on the effectiveness of pallidal surgery on the L-dopa induced dyskinesias, but, its long-term effects on tremor, akinesia, freezing of the gait and other genuine parkinsonian symptoms need more extensive evaluation. The assessment of the outcome of pallidal surgery in terms of the patient's disability, quality of life and coping abilities following surgery seems to have been neglected.

Electrophysiologic target localization in posteroventral pallidotomy

The current interest in stereotactic posteroventral pallidotomy (PVP) for treating Parkinson's disease and the variability of published results have raised questions regarding techniques for target localization. In our technique the probe is guided to the optimum target at the most ventral pallidum and ansa lenticularis by macroelectrode stimulation of the internal capsule and optic tract from within the globus pallidus, with the thresholds providing a relative measure of the electrode proximity to these structures. We have characterized these localizing macroelectrode stimulation parameters in 57 posteroventral pallidotomies with consistent anatomic lesion placement, excellent outcome, and no complications. Using a 1.8 x 2.0 mm radiofrequency electrode for macroelectrode stimulation (RFG-3C, Radionics Inc.), minimum voltages (thresholds) to activate motor (at a frequency of 2 Hz) or visual (at a frequency of 100 Hz) responses as well as impedance measurements were obtained at the final target (Tf) and at distances proximal to Tf along the electrode trajectory. The visual and motor threshold voltages at Tf via our standard approach angles (50 degrees above base plane, 20 degrees from the sagittal plane), had a range of 1.0 to 1.5 V, and 2.0 to 3.5 V respectively. We also found that as the probe approaches Tf there is a significant decrease in voltage thresholds for motor (P < .0001) and visual (P < .0001) responses in an individual patient indicating that the probe is converging on these structures. Increases in impedance between Tf, 2-3 mm, and 4-5 mm proximal to Tf were also statistically significant (P < .0001). Microelectrode recording to electrophysiological neuronal activity at various points along the trajectory towards the target showed distinct firing patterns providing identification of the globus pallidus externus and internus, ansa lenticularis, and optic tract. Macroelectrode electrophysiological stimulation within the target volume, inducing threshold responses in the internal capsule and optic tract, provides for accurate localization of the most effective PVP target in the ansa lenticularis. In unresponsive patients, the utilization of microelectrode recording for the identification of the pallidal borders and the optic tract improves safety.

Role of stereotaxis in the treatment of cerebral palsy

There is a renewed interest in basal ganglia surgery for improvement of motor symptoms in cerebral palsy. Rigidity, choreoathetosis, and tremor can be improved or abolished by a well-placed radiofrequency lesion, either in the ventrolateral nucleus of the thalamus or ventroposterior pallidum. The target is chosen based on the predominance of the symptoms in a given patient. A review of the main reports on surgery of the basal ganglia for cerebral palsy, as well as the author's data, shows that the surgery can have a remarkable impact on patients' quality of life when motor dysfunction is improved. An update of the physiopathology of cerebral palsy motor symptoms related to anatomic findings on experimental work, magnetic resonance imaging, and autopsy is used to rationalize surgery of the basal ganglia. Modern stereotactic technique based on exquisite demonstration of the basal ganglia anatomy by magnetic resonance imaging is described and supported by intraoperative electricophysiologic studies. The author stresses the importance of a multidisciplinary approach to provide the cerebral palsy patient with a comprehensive treatment plan before stereotactic surgery.