Surgery for intramedullary spinal cord tumors: the role of intraoperative (neurophysiological) monitoring

In spite of advancements in neuro-imaging and microsurgical techniques, surgery for intramedullary spinal cord tumors (ISCT) remains a challenging task. The rationale for using intraoperative neurophysiological monitoring (IOM) is in keeping with the goal of maximizing tumor resection and minimizing neurological morbidity. For many years, before the advent of motor evoked potentials (MEPs), only somatosensory evoked potentials (SEPs) were monitored. However, SEPs are not aimed to reflect the functional integrity of motor pathways and, nowadays, the combined used of SEPs and MEPs in ISCT surgery is almost mandatory because of the possibility to selectively injury either the somatosensory or the motor pathways. This paper is aimed to review our perspective in the field of IOM during ISCT surgery and to discuss it in the light of other intraoperative neurophysiologic strategies that have recently appeared in the literature with regards to ISCT surgery. Besides standard cortical SEP monitoring after peripheral stimulation, both muscle (mMEPs) and epidural MEPs (D-wave) are monitored after transcranial electrical stimulation (TES). Given the dorsal approach to the spinal cord, SEPs must be monitored continuously during the incision of the dorsal midline. When the surgeon starts to work on the cleavage plane between tumor and spinal cord, attention must be paid to MEPs. During tumor removal, we alternatively monitor D-wave and mMEPs, sustaining the stimulation during the most critical steps of the procedure. D-waves, obtained through a single pulse TES technique, allow a semi-quantitative assessment of the functional integrity of the cortico-spinal tracts and represent the strongest predictor of motor outcome. Whenever evoked potentials deteriorate, temporarily stop surgery, warm saline irrigation and improved blood perfusion have proved useful for promoting recovery, Most of intraoperative neurophysiological derangements are reversible and therefore IOM is able to prevent more than merely predict neurological injury. In our opinion combining mMEPs and D-wave monitoring, when available, is the gold standard for ISCT surgery because it supports a more aggressive surgery in the attempt to achieve a complete tumor removal. If quantitative (threshold or waveform dependent) mMEPs criteria only are used to stop surgery, this likely impacts unfavorably on the rate of tumor removal.

     

Diffusion-tensor imaging-guided tracking of fibers of the pyramidal tract combined with intraoperative cortical stimulation mapping in patients with gliomas

OBJECT: The goal of this study was to use diffusion-tensor (DT) magnetic resonance (MR) imaging to track fibers combined with cortical stimulation mapping to delineate descending motor pathways. Subcortical localization of motor pathways in relation to a glioma may provide critical information to guide tumor resection and prevent surgical morbidity. METHODS: Eleven adult patients harboring gliomas underwent MR imaging 1 day prior to image-guided intraoperative cortical motor mapping and tumor resection. Screens depicting 27 cortical motor sites on a surgical navigation system were saved to launch DT imaging of fiber tracks of descending motor pathways. The position and organization of motor tracts were visualized by fiber tracking. Tracks from 16 motor stimulation sites followed descending pathways from the precentral gyrus, through the corona radiata and internal capsule, and into the cerebral peduncle. These tracks were also observed on DT images to diverge along crossing white matter bundles (four patients) and to terminate or deviate in regions of peritumoral vasogenic edema (five patients). CONCLUSIONS: The use of precise intraoperative cortical mapping information and DT images of fiber tracks can reveal the course of motor pathways beneath the cortex. The subcortical fiber tracks generated are consistent with the known anatomical course and somatotopic organization of the motor tract in relation to its cortical origins. Tracking fibers by using DT imaging in combination with functional localization has the potential to reduce surgical morbidity by revealing subcortical connections of the functional cortex.     

Intraoperative electrocortical stimulation of Brodman area 4: a 10-year analysis of 255 cases

Background

Brain tumor surgery is limited by the risk of postoperative neurological deficits. Intraoperative neurophysiological examination techniques, which are based on the electrical excitability of the human brain cortex, are thus still indispensable for surgery in eloquent areas such as the primary motor cortex (Brodman Area 4).

Methods

This study analyzed the data obtained from a total of 255 cerebral interventions for lesions with direct contact to (121) or immediately adjacent to (134) Brodman Area 4 in order to optimize stimulation parameters and to search for direct correlation between intraoperative potential changes and specific surgical maneuvers when using monopolar cortex stimulation (MCS) for electrocortical mapping and continuous intraoperative neurophysiological monitoring.

Results

Compound muscle action potentials (CMAPs) were recorded from the thenar muscles and forearm flexors in accordance with the large representational area of the hand and forearm in Brodman Area 4. By optimizing the stimulation parameters in two steps (step 1: stimulation frequency and step 2: train sequence) MCS was successful in 91% (232/255) of the cases. Statistical analysis of the parameters latency, potential width and amplitude showed spontaneous latency prolongations and abrupt amplitude reductions as a reliable warning signal for direct involvement of the motor cortex or motor pathways.

Conclusion

MCS must be considered a stimulation technique that enables reliable qualitative analysis of the recorded potentials, which may thus be regarded as directly predictive. Nevertheless, like other intraoperative neurophysiological examination techniques, MCS has technical, anatomical and neurophysiological limitations. A variety of surgical and non-surgical influences can be reason for false positive or false negative measurements.     

Demonstration of Cerebral Plasticity by Intra-Operative Neurophysiological Monitoring: Report of an Uncommon Case

Summary  It has been postulated long ago that “eloquent” areas shift their location in patients with arteriovenous malformations (AVM). Obviously the “motor region” in not located in the precentral gyrus in a patient with an AVM in the “motor region”.  We report on the case of a 15-year old boy with an AVM in the left sensorimotor cortex, in whom intra-operative mapping showed an inexcitability of the precentral gyrus, while stimulation of the cortex anterior to the primary motor cortex elicited motor responses. This indicates that motor function was translocated from the primary to the supplementary motor cortex. Surgery was performed under general anaesthesia. Neurophysiological monitoring was performed throughout surgery. The central sulcus was identified by phase reversal of the somatosensory evoked potentials. The motor cortex was mapped by direct high-frequency (500 Hz) monopolar anodal stimulation.  In the patient herein reported, stimulation of the “anatomically” defined primary motor cortex induced no motor response, as expected. Motor response was elicited only by stimulation of the cortex anterior to the precentral gyrus. There was no postoperative deterioration of motor function. These observations indicate that the precentral gyrus was functionally “useless”. The motor region was relocated into more rostral areas in the supplementary motor cortex. This translocation of function in the presence of an AVM indicates cerebral plasticity.     

Transcranial electrical stimulation through screw electrodes for intraoperative monitoring of motor evoked potentials. Technical note

The feasibility of high-frequency transcranial electrical stimulation (TES) through screw electrodes placed in the skull was investigated for use in intraoperative monitoring of the motor pathways in patients who are in a state of general anesthesia during cerebral and spinal operations. Motor evoked potentials (MEPs) were elicited by TES with a train of five square-wave pulses (duration 400 microsec, intensity < or = 200 mA, frequency 500 Hz) delivered through metal screw electrodes placed in the outer table of the skull over the primary motor cortex in 42 patients. Myogenic MEPs to anodal stimulation were recorded from the abductor pollicis brevis (APB) and tibialis anterior (TA) muscles. The mean threshold stimulation intensity was 48 +/- 17 mA for the APB muscles, and 112 +/- 35 mA for the TA muscles. The electrodes were firmly fixed at the site and were not dislodged by surgical manipulation throughout the operation. No adverse reactions attributable to the TES were observed. Passing current through the screw electrodes stimulates the motor cortex more effectively than conventional methods of TES. The method is safe and inexpensive, and it is convenient for intraoperative monitoring of motor pathways.     

Intraoperative DTI and brain mapping for surgery of neoplasm of the motor cortex and the corticospinal tract: our protocol and series in BrainSUITE

We report our preliminary series of patients treated for lesions involving the motor cortex and the corticospinal tract in BrainSuite, with intraoperative MRI, tractography and "neuronavigated" electrophysiological cortical and subcortical mapping. An exact localization of the cortical and subcortical functional areas is mandatory for executing surgery of intra-parenchymal neoplasm involving the motor cortex and the corticospinal tract. Nowadays modern technology offers a variety of tools to reduce as much as possible postoperative deficits during surgery of cerebral eloquent areas. From December 2008 and June 2010, 18 patients underwent functional surgery, for neoplasm involving the motor cortex and/or the subcortical pathway, in BrainSuite. Our preliminary series include 14 gliomas and 4 metastases; Table 1 summarizes all of the data. We included in this series patients with complete removal of lesions of eloquent areas with an average distance from the corticospinal tract of 4 mm. Six neoplasms were considered in contact and/or involving the motor cortex, while in 18 cases (100%) the tumour involved eloquent areas concerning the corticospinal tract. All of the patients underwent complete removal of the lesion as subsequently demonstrated by intraoperative postsurgical MRI. Our series highlights the good integration and the high compatibility between BrainSUITE with 1.5 T intraoperative magnetic field and neurophysiological monitoring. We strongly believe that intraoperative MRI with DTI allows us to treat complex surgery tumours that without its auxilium we would not be able to deal with.     

Primary thumb sensory cortex located at the lateral shoulder of the inverted omega-shape on the axial images of the central sulcus

Useful landmarks on magnetic resonance (MR) images were identified for preoperative prediction of the relationship of a tumor to the primary sensory cortex of the thumb. Functional MR (fMR) imaging and magnetoencephalography were used to retrospectively localize the hand-digit sensorimotor area in four patients who underwent tumor resection around the central sulcus with intraoperative neurophysiological mapping. fMR imaging revealed the hand-digit motor cortex in the so-called "precentral knob" inside the characteristic inverted-omega on axial MR images. Equivalent current dipoles of the N20 m response in somatosensory evoked fields (SEFs) of the thumb, median nerve, and ulnar nerve stimuli were localized at the lateral portion of the inverted omega-shape from the lateral to medial directions. The SEF-based thumb sensory cortex was verified by intraoperative functional mapping with a neuronavigation system. The hand-digit somatosensory cortices were localized at the lateral shoulder of the inverted-omega, in the lateral anterior inferior position to the hand-digit motor cortices in the precentral knob. Axial MR imaging can provide useful preoperative planning information for the surgical treatment of tumors within or adjacent to the motor-somatosensory cortex.     

Surgical resection of grade II astrocytomas in the superior frontal gyrus

OBJECTIVE: Surgery in the superior frontal gyrus partially involving the supplementary motor area (SMA) may be followed by contralateral transient weakness and aphasia initially indistinguishable from damage to the primary motor cortex. However, recovery is different, and SMA deficits may resolve completely within days to weeks. No study has assessed the distinct postoperative deficits after tumor resection in the SMA on a homogeneous patient group. METHODS: Twenty-four patients with World Health Organization Grade II astrocytomas in the superior frontal gyrus consecutively treated by surgery were studied. Degree and duration of postoperative deficits were evaluated according to tumor location and boundaries via magnetic resonance imaging scans, intraoperative neuromonitoring results, and extent of tumor resection. RESULTS: Postoperatively, motor deficits were evident in 21 of 24 and speech deficits in 9 of 12 patients. Motor function quickly recovered in 11 and speech function in 3 patients. None of the 12 patients in whom the posterior tumor resection line was at a distance of more than 0.5 cm from the precentral sulcus experienced persistent motor deficits. Eight of these patients developed typical SMA syndrome with transient initiation difficulties. Seven of 12 patients in whom the tumor extended to the precentral sulcus still had motor deficits at the 12-month follow-up assessment. CONCLUSION: Surgery for Grade II gliomas in the superior frontal gyrus is more likely to result in permanent morbidity when the resection is performed at a distance of less than 0.5 cm from the precentral gyrus or positive stimulation points. Therefore, cortical mapping of motor and speech function, in critical cases under local anesthesia with the patient as his or her own monitor, is recommended; resection should be tailored to obtain good functional outcome and maintain quality of life.     

Monitoring of muscle motor evoked potentials during cerebral aneurysm surgery: intraoperative changes and postoperative outcome

OBJECT: The authors in this study evaluated muscle motor evoked potentials (MMEPs) elicited by transcranial electrical stimulation (TES) and direct cortical stimulation as a means of monitoring during cerebral aneurysm surgery. The analysis focused on the value and frequencies of any intraoperative changes and their correlation to the postoperative motor status. METHODS: One hundred nineteen patients undergoing surgery for 148 cerebral aneurysms were included in the study. Muscle motor evoked potentials were elicited by a train of five constant-current anodal stimuli with an individual pulse duration of 0.5 msec and a stimulation rate of 2 Hz. Stimulation intensity was up to 240 mA for TES and up to 33 mA for direct cortical stimulation. The MMEPs were continuously recorded from the abductor pollicis brevis and tibialis anterior muscles bilaterally and from the biceps brachii and extensor digitorum communis muscles contralateral to the surgical side. The motor status was evaluated immediately after surgery and 7 days later. In 97% of the patients MMEPs were recordable for continuous neurophysiological monitoring of the vascular territory of interest throughout the surgery. In 14 patients significant intraoperative MMEP changes occurred, resulting in a transient motor deficit in one patient and a permanent motor deficit in six. The permanent loss of MMEPs in three patients was followed by a permanent severe motor deficit in one patient and severe clinical deterioration in the other two. CONCLUSIONS: Data in this study demonstrated that MMEPs are a useful means of intraoperative neurophysiological monitoring of motor pathway integrity and predicting postoperative motor status. The intraoperative loss of MMEPs reliably predicts both severe and permanent postoperative motor deficits.     

Presurgical mapping with functional MRI: comparative study with transcranial magnetic stimulation and intraoperative mapping]

PURPOSE: The accuracy of preoperative mappings in patients with brain tumors near the central sulcus using functional magnetic resonance imaging (fMRI) or transcranical magnetic stimulation (TCS) was evaluated by comparative reference to intraoperative mapping. METHODS: The thumb movement was evoked by TCS for the mapping of the motor cortex. After the placement of the marker determined by TCS on the scalp, fMRI under motor tasks consisting of repetitive grasping was performed. For motor cortex activation, an axial oblique plane to maximize gray matter sampling in the rolandic cortex was employed in order to compare these different mapping techniques more precisely. Sixteen patients with brain tumors were included in this study. RESULTS: In nine patients, fMRI disclosed activation in one restricted gyrus or in the localized area around one restricted sulcus. Of these nine patients, preoperative TCS mapping corresponded closely with fMRI in six, while in the remaining three, the TCS marker fell between 1 and 2 cm apart from the fMRI-activated area. However, in these three patients, intraoperative electrocortical stimulation corresponded with the preoperative mapping with fMRI. In six patients, contigucus two gyri were activated by motor tasks. The TCS marker was disclosed on one of the two activated gyri. Of these six patients, the position of the TCS marker and fMRI-activated site corresponded with each other in four cases. They were found on the same gyrus but there was 1.0-2.0 cm distance between them in two cases. Intraoperative somatosensory evoked potential was monitored in two of these six cases. They corresponded well with the mapping by fMRI and TCS together. In only one patient, no significant activation area was obtained by fMRI because of excessive head motion during motor tasks. The TCS marker in this patient was identical with intraoperative electro-cortical stimulation mapping. CONCLUSION: For presurgical planning in patients with brain tumor near the central sulcus, comparative evaluation with fMRI and TCS is applicable and provides accurate functional mapping.     

Impact of Brain Shift on Intraoperative Neurophysiological Monitoring with Cortical Strip Electrodes

Summary.  Background: Intraoperative neurophysiological monitoring has become the standard procedure for locating eloquent regions of the brain. Such continuous electrical stimulation of motor pathways is usually applied by means of flat silicon-embedded electrodes placed directly on the motor cortex. However, shifting of the silicon strip on the cortical surface as well as electrode displacement due to brain shift underneath the electrode can lead to inaccurate recordings not directly caused by intraoperative impairment of the motor cortex or the motor pathways.  Method: This prospective study was conducted to quantify cortical brain shift during open cranial surgery and to assess its impact on electrode positioning in 31 procedures near the precentral gyrus. Three groups of different lesion volumes were distinguished. Movement of the cortex between opening of the dura and completion of tumor removal as well as cortical electrode shifting were digitally measured and analyzed.  Findings: Cortical surface structures evidenced a significantly larger shift (up to 23.4 mm) in comparison to the electrode strips (up to 4.2 mm) in lesions with a volume of over 20 ml. Cortex shifting highly correlated with lesion volume, whereas strip electrode movement was almost unidirectional and did not differ significantly among the three groups. However, the way they were placed (completely on the cortex vs. partly underlying or overlapping the craniotomy borders) affected the magnitude of their intraoperative displacement. As a consequence, 3 of the 31 cases (9.3%) showed a significant change in the recorded motor responses due to intraoperative dislocation of the stimulating electrode.  Interpretation: Changes in the location of cerebral structures due to intraoperative brain shift may exert a marked influence on intraoperative neurophysiological monitoring if cortical strip electrodes are used. Therefore, long-term monitoring of the central region requires continuous checking of the position of stimulating electrodes and, if necessary, correction of their location. Published online December 5, 2002 Acknowledgments  The authors thank Mr. Udo Warschewske and his co-workers of Functional Imaging Technologies (Waltersdorf, Land Brandenburg, Germany) for their help in establishing the software necessary for the navigation-controlled calculation of intraoperative brain and electrode shifting.  Correspondence: Dr. med. Olaf Suess, Department of Neurosurgery, Benjamin Franklin University Hospital, Free University of Berlin, Hindenburgdamm 30, 12200 Berlin, Germany.     

Intraoperative neurophysiologic monitoring during syringomyelia surgery: lessons from a series of 13 patients

Background

Avoiding iatrogenic neurological injury during spinal cord surgery is crucially important. Intraoperative neurological monitoring (INM) has been widely used in a variety of spinal surgeries as a means of reducing the risk of intraoperative neurological insults. This study evaluates the benefits of INM specifically in spinal procedures for treatment of syringomyelia.

Methods

Thirteen patients who underwent surgery for syrinx drainage with the assistance of INM were included in this study. In all patients both somatosensory-evoked potentials (SSEP) and motor-evoked potentials (MEP) were monitored. INM data and perioperative neurological evaluations were both recorded and analyzed.

Results

Eleven patients underwent syringo-subarachnoid shunt (SSAS) surgery. One patient underwent syrinx drainage and foramen magnum decompression (FMD). One patient underwent syringo-pleural shunt (SPA) surgery. Baseline MEP and SSEP were recordable at the beginning of surgery in 11 patients (>84 %). In the other two cases, baseline data from specific INM modalities were absent, correlating with the antecedent neurologic symptomotology. Two patients exhibited significant intraoperative changes in MEP data that influenced the course of surgery and prompted removal or re-insertion of the shunt. Mild and transient worsening of preoperative symptoms was reported in these instances. No new postoperative neurological deficits were reported in the other 11 patients in whom INM data were preserved throughout surgery.

Conclusion

These data support routine use of INM in syringomyelia surgery. INM can alert the surgeon to potential intraoperative threats to the functional integrity of the spinal cord, providing a useful adjunct to spinal cord surgeries for the treatment of syringomyelia.     

Clinical features and significance of negative motor response in intraoperative language mapping during awake craniotomy

The negative motor area and anterior and posterior language areas were localized by intraoperative electrical cortical stimulation under the awake condition to evaluate the clinical significance of these areas. Thirty-seven awake craniotomies with language mapping were performed in 36 patients with brain tumors. The negative motor area was determined in 17 cases, and the anterior and posterior language areas were found in 12 and 6 cases, respectively. The negative motor area was located in the precentral gyrus inferior to the orofacial motor area in 16 cases, and in the inferior frontal gyrus anterior to the orofacial motor area in one case. Both the negative motor area and the anterior language area were determined in 8 cases. Anterior language areas in these 8 cases were located anterior and/or inferior to the negative motor areas. The negative motor area is an easily determined, important landmark for intraoperative language mapping.     

Localization of human sensorimotor cortex during surgery by cortical surface recording of somatosensory evoked potentials

The traditional means of localizing sensorimotor cortex during surgery is Penfield's procedure of mapping sensory and motor responses elicited by electrical stimulation of the cortical surface. This procedure can accurately localize sensorimotor cortex but is time-consuming and best carried out in awake, cooperative patients. An alternative localization procedure is presented that involves cortical surface recordings of somatosensory evoked potentials (SEP's), providing accurate and rapid localization in patients under either local or general anesthesia. The morphology and amplitude of median nerve SEP's recorded from the cortical surface varied systematically as a function of spatial location relative to the sensorimotor hand representation area. These results were validated in 18 patients operated on under local anesthesia in whom the sensorimotor cortex was independently localized by electrical stimulation mapping; the two procedures were in agreement in all cases. Similar SEP results were demonstrated in an additional 27 patients operated on under general anesthesia without electrical stimulation mapping. The following three spatial relationships between SEP's and the anatomy of the sensorimotor cortex permit rapid and accurate localization of the sensorimotor hand area: 1) SEP's with approximately mirror-image waveforms are recorded at electrode sites in the hand area on opposite sides of the central sulcus (P20-N30 precentrally and N20-P30 postcentrally); 2) the P25-N35 is recorded from the postcentral gyrus as well as a small region of the precentral gyrus in the immediate vicinity of the central sulcus: this waveform is largest on the postcentral gyrus about 1 cm medial to the focus of the 20- and 30-msec potentials; and 3) regardless of component identification, maximum SEP amplitudes are recorded from the hand representation area on the precentral and postcentral gyri.     

Functional brain mapping of patients with arteriovenous malformations using navigated transcranial magnetic stimulation: first experience in ten patients

Background

Intracranial arteriovenous malformations (AVM) are known to be potent inductors of functional plasticity, and their vasculature makes standard functional imaging difficult. Here we conducted functional mapping of both primary motor cortex and speech related areas in patients with AVM using navigated transcranial magnetic stimulation (nTMS), which has been recently proven as a reliable noninvasive modality of preoperative functional brain mapping.

Method

nTMS mapping was performed in ten patients with unruptured intracranial AVMs located in or near eloquent areas. Motor mapping was conducted for six patients with AVMs near the rolandic region, and speech mapping was performed for four patients with left perisylvian AVMs. After the examination, all patients were treated with surgery, radiosurgery or observed with best medical treatment on case-by-case basis.

Results

Motor mapping allowed for delineation of the primary motor cortex, even if the anatomy was severely obscured by the AVM in all cases with rolandic AVMs. No plastic relocation of the primary motor cortex was observed. Repetitive stimulation of the left ventral precentral gyrus led to speech impairments in all four cases that underwent speech mapping. Right hemispheric involvement was observed in one out of four cases and potentially indicated plastic changes. No side effects were observed.

Conclusion

nTMS allowed for detailed delineation of eloquent areas even within hypervascularized cortical areas. Our observations indicate that nTMS functional mapping is feasible not only in tumorous brain lesions, but also in AVMs.     

Intraoperative monitoring of the corticospinal motor evoked potential (D-wave): clinical index for postoperative motor function and functional recovery

The corticospinal motor evoked potential was investigated as a monitoring index of motor function to perform maximal resection of brain tumors located around the motor cortex in 37 patients with glioma. Tumor resections were performed under general anesthesia with muscle relaxant and completely controlled ventilation. No special arrangements for anesthesia were required. Direct cortical stimulation revealed that if one electrode was placed on the posterior half of the precentral gyrus, the D-wave could be recorded even when using an electrode separation of 10 mm, and the amplitude was larger with anodic rather than cathodic stimulation. Monitoring of the D-wave enabled the function of the corticospinal tract to be evaluated selectively. Postoperative persistent motor disturbance remained in six patients who had a decrease of over 30% in amplitude of the D-wave during tumor resection. A decrease of less than 30% may indicate postoperative preservation of motor function, including transient motor disturbance with subsequent complete recovery. Intraoperative monitoring of the D-wave is suitable for open cranial surgery with general anesthesia, can detect the primary motor cortex, and allow maximal resection of brain tumors located around the motor cortex.     

Motor evoked potentials

Motor dysfunction following spinal surgery and thoracoabdominal aortic surgery remain as one of their devastating complications. Since the development of postoperative motor dysfunction can deteriorate quality of life of patients, the prevention of such complications is an important clinical challenge. Recently, advances in stimulation technique using multipulse made intraoperative monitoring of functional integrity of motor pathways possible by recording myogenic motor evoked potentials (MEPs). However, myogenic MEPs can be affected by most of anesthetic agents and muscle relaxants. Anesthesiologists are therefore required to properly understand MEPs and to manage anesthesia carefully. We summarize the methods for monitoring of myogenic MEPs and anesthetic techniques during intraoperative MEP monitoring.     

Localization of central lesions by correlation of CT findings and neurological deficits

Summary In a prospective study involving 100 patients with lesions in the precentral gyrus or pyramidal tract we sought to correlate clinical findings and the results of an axial computed tomography (CT) to localize the lesion. In 85% of patients the size and location of the lesion visible on CT correlated well with the type and severity of the neurological symptoms and signs. However, in the remaining 15% of patients the CT findings did not correlate well with the patient's neurological deficit, showing that in these patients the anatomy of the central area was variable or distorted by the space-occupying lesion. We suggest that in such patients neurophysiological techniques be used intra-operatively for reliable localization of the motor strip.     

功能磁共振成像定位皮质运动区与术中电刺激运动诱发电位的前瞻对照研究

目的以术中电刺激运动诱发电位（MEP）监测为对照,评价中央区脑肿瘤术前运用血液氧饱和水平检测（BOLD）技术的功能磁共振成像（fMRI）定位皮质运动区的准确性。方法此项前瞻性研究选取了16例中央区脑肿瘤。开颅手术前分别执行手运动激发程式,运用BOLD技术的fMRI定位皮质运动区。将fMRI影像与磁共振导航序列影像融合。以术中MEP监测作为皮质运动区定位的标准技术。在神经导航下定位fMRI的各个激活区,单独或联合运用短串经颅电刺激（TCES）和直接皮质电刺激（DCES）,在前臂及手部记录复合肌肉动作电位。比较两种技术的吻合度,以评价fMRI定位的皮质运动区的准确性。结果fMRI与MEP的吻合率为92．3％,其中与TCES的吻合率为100．0％,与DCES的吻合率为66．7％。结论运用BOLD技术的fMRI敏感度高,可实现中央区脑肿瘤术前皮质运动区的准确定位。     

Usefulness of direct electrical stimulations during surgery for gliomas located within eloquent brain regions

Glioma surgery in functional areas has undergone a dramatic development these last few years, thanks to improvements in both intraoperative functional imaging and direct electrical stimulation of cortical areas or association pathways. The goal of these techniques to achieve complete as possible surgical removal of tumors located in eloquent areas (sensitive, motor and language areas) with minimal risk of permanent sequelae. To be reliable, a rigorous methodology is required. Current cortical mapping is very easy to achieve, whereas mapping of association pathways will require much more experience. In case of tumors located in somatosensorial or language areas, the difficulties related to accurate sub cortical localization are combined with these of local anesthesia and the best task choice to evaluate the integrity of cognitive functions. These functional techniques allow total or sub total removal in 52% to 76.2% of patients. Transient worsening is observed in 13% to 80% of the patients; the rate of permanent sequelae averages 4%.