- Email: [email protected]
P245 Surgery of intrinsic lesions in the motor strip: A stereotactically guided minicraniotomy with electrophysiological mapping of the motor cortex
328
Poster Session: lntraoperative and Intensive Care Monitonng Procedures
tween the EEG, recorded from healthy persons and patients with neurotoxic diseases. The most informative parameters for diagnozing of hypersthenic neurotoxic syndrome were the 0/3-activities EEG of temporofrontal parts.
rP-~
COMPLEXITY OF STATE SPACE TRAJECTORIES OF MULTICHANNEL EEG MAP SERIES DURING OPEN AND CLOSED EYES
I. Kond~ikor ].2, D. Lehmann i, Jiri Wackermann, T. Kocnig J, T. Yagyu ], K. Kechi i . i The KEY lnstitutefor Brain-Mind Research, University
Hospital of Psychiatry, Zurich, Switzerland; 2 Department of Neurology, University Medical School, P~cs, Hungary; Neuroscience Technology Research, Prague, Czech Republic Series of momentary potential maps of multichannel EEG data can be viewed as trajectories in state space. Topological properties of the shape of the trajectories during different functional states of the brain can be assessed by Global Dimensional Complexity (GDC) and by Global OMEGAComplexity (Omega). Using these two nonrelated methods, we studied 27channel EEG data of 12 healthy subjects under two no-task conditions: eyes closed and open. For both analyses the same artifact-free, 2 sec epochs (256 datapoints) of the band-passed EEG (1.5-32.0 Hz) were analyzed. For each subject the two measures were determined for each epoch (mean 73 epochs/subject, S.D. = 18). GDC as well as Omega increased significantly under the eyes open condition: mean (N = 12) GDC changed from 5.78 to 6.18 (t = 5.91, p 0001), mean Omega from 5.50 to 6.93 (t = 5.10, P 0004). Our results indicate that there are more independent, parallel, functional processes activated during the open eyes state than during the closed eyes state of the brain.
~
CLINICAL AND QUANTITATIVE EEG EVALUATION OF THE EFFICACY OF THE TREATMENT WITH LAMOTRIGINE
V.F. Roman, C.F. Roman. Inst. of Public Health, Targu-Mures, Romania Lamotrigine appears to be an antiepileptic drug with great perspective in the treatment of the complex partial seizures refractory to treatment. Lamotrigine stabilise the neuronal membrane (blocks the calcium and sodium channels) and inhibit the release of the glutamate. We evaluated the efficacy of the treatment with Lamotrigine in 24 patients with partial complex seizures refractory to treatment treated one year with this antiepileptic drug. The efficacy of the treatment has been evaluated by the reduction of number of crisis and by the EEG quantitative changes, using the BEAM (Brain Electrical Activity Mapping). For an exact evaluation of the efficacy of treatment (reduction of number of crisis) was use the response ratio for each cases. For each patient was accomplish the BEAM, initially in the first month, afterwards to 3 months. To all the cases the response ratio shows a reduction of number of crisis over 50%. The BEAM shows a clear influence among secundars foci and the reduction of the activity of dominant foci.
underwent a clinical neurological examination and SEPs on the day before and one week after surgery. We recorded SEPs during the entire course of surgery - at intervals of 3 to 5 minutes immediately before, during and immediately after carotid clamping and at intervals of 10 to 20 minutes during the remaining periods. For each recording, we assessed the latency of the spinal peak N13 and that of the cortical peak N20, in addition we measured the amplitude P15/N20 and N20/P25. Moreover, arterial blood pressure and the course of surgery were closely recorded. The aim of the study is to define critical values of intraoperative SEP changes. Inclusion of patients will be continued until August 31. Detailed data will be presented.
~-~
S. Anton i, E. Castro 2, F. Corral 3 V. Ibarrola i, j. Brasa 2, L. Nombela 2.
I Servicio de lVeurofisiologia, Clinica Puerta de Hierro, Madrid, Spain; 3 Servicio de Neurologia, Clinica Puerta de Hierro, Madrid, Spain; 2 Servicio de Neuroradiologia, Clinica Puerta de Hierro, Madrid, Spain We have studied 79 patients who had EEG monitoring during the implantation of electrical coils in intracranial aneurysms at the Puerta de Hierro Clinic. Patients were sedated and heparinized. A microcatbeter was introduced until the aneurysm was reached. Within the microcatheter, a coil comprising a wire guide of stainless steel and a platinum circular memory at the distal end was introduced inside the aneurysm. A positive electrical current was applied to the proximal end of the guide to induce electrothrombosis at the platinum end and electrolysis at the steel-platinum interface. The procedure is presently indicated as an alternative to surgery when the latter is not feasible. An initial awake EEG was recorded, followed by continuous EEG monitoring during the procedure. Attention was paid to early detection of potential complications: vascular spasm, haemorrhage, coil migration, embolism and tolerance test. Early results from treatment were occasionally observed. Seventy nine patients were studied: 25 men (32%) and 54 women (68%), range: 18-75. Clinical presentation: 80% SAH, 15% mass effect and 5% asymptomatic. Localization: in 5 patients the aneurysm was localized in CA, 10 in Ophtalm art, 4 in Cavernous sinus, 12 in communicating ant art, 7 in MCA, 19 in Communicating post art, 21 in Basilar art, 3 in Posterior cerebral art and 1 in PICA. 30% were in the posterior circulation. The size of the aneurysm was between 0.6 and 3 cm. The number of coils introduced during each session was between 1 and 10, most frequently 2-3. Immediate complications: 4 transitory, 1 definite (death). Late complications: 1 transitory, 1 permanent. We considered that EEG monitoring during coil implantation in intracraneal aneurysms is useful as an objective method to assess the ongoing brain activity and helps the neuroradiologist decide whether to continue or halt the procedure.
~-4-~
Intraoperative and Intensive Care Monitoring Procedures MONITORING OF MEDIAN NERVE SOMATOSENSORY EVOKED POTENTIALS DURING CAROTID SURGERY Ch. Wtiber ], J. Zeitlhofer i, S. Asenbaum 1 L. Claeys z, p. Polterauer 2
] Dept. of Neurology, University of Vienna, Austria; 2 Dept. of Vascular Surge~; University of Vienna, Austria During carotid surgery cerebral blood flow may decrease to a critical level causing remitting or permanent neurological deficits. Clinical examination does not allow to detect these changes during surgery. Therefore, it is essential to provide monitoring techniques which allow an intraoperative assessment of cerebral function. We have used median nerve somatosensory evoked potentials (SEPs) for intraoperative monitoring during carotid surgery. In addition, all patients
NEUROPHYSIOLOGICAL MONITORING IN ENDOVASCULAR TREATMENT OF INTRACRANIAL ANEURYSMS VIA ELECTRICAL COILS
SURGERY OF INTRINSIC LESIONS IN THE MOTOR STRIP: A STEREOTACTICALLY GUIDED MINICRANIOTOMY WITH ELECTROPHYSIOLOGICAL MAPPING OF THE MOTOR CORTEX
W. Eisner i, U. Steude l, K. Bise 2, U.D. Schmid i. 1 Dept. of
Neurosurgery, LMU Munich, Germany; 2 Institute of Neuropathology, LMU Munich, Germany Introduction: Surgery of space occupying lesions that are located subcortically in the central motor area carries a considerable risk of postoperative palsy, We wanted to prove whether a stereotactically guided craniotomy and localisation of the lesion will reduce the incidence of a new postoperative permanent sensorimotor deficit by using electrophysiological mapping of the motor cortex. Material and method: Since April 1992, a series of about 100 patients was operated for tumors that were located in or adjacent to the sensorimotor strip. We routinely used motor cortex mapping using Penfields procedure (5--40 mA, 50Is, 0.2 ms) under general anesthesia without neuromuscular blocking agents. 11 of these patients had their lesion located subcortically, their diameter was < 20 mm. These lesions were operated using additionally a stereotactically guided minicraniotomy of < 30 m m in diameter.
Poster Session: lntraoperative and Intensive Care Monitoring Procedures Results: Based on the intraoperative histological samples and on postoperative MRI/CT, all lesions could be removed completely. All 11 patients had a preoperative motor weakness in at least one contralateral limb, which resolved within 10 days after surgery in all cases. Conclusions: Stereotaxy allows a mini-craniotomy that is hardly larger than the target lesion, thus minimizing surgical exposure of the adjacent cortex. This leads to loss of anatomical landmarks, especially of the topography of the sensorimotor strip, that can be compensated by electrophysiological mapping of the motor cortex, thus enabling the surgeon to define to preserve, the motor cortex during surgery.
[-~-~
MOTOR EVOKED POTENTIAL MONITORING DURING SURGICAL PROCEDURES IN THE CENTRAL AND INSULAR REGION
U. Pechstein, J. Zentner, C. Cedzich, J. Schramm. Department of
Neurosurgery, UniversiO, of Bonn, Germany Introduction: Surgical procedures within the central region and the insular cortex harbor the risk of postoperative motor deficits. We present our experience with motor evoked potential (MEP) monitoring during surgery of supratentorial lesions in the near vicinity of eloquent areas of the brain. Patients and Methods: 91 patients (39 females, 52 males) with a mean age of 47 years (3-78 years), who were operated on lesions of the central and insular region received intraoperative MEP monitoring. After localization of the central sulcus by means of SEP phase reversal, MEP from forearm flexor muscles, thenar and hypothenar were recorded in response to direct cortical high frequency electric stimulation of the motor cortex in 85 patients. 6 patients with tumors of the insular region were monitored with MEP after transcranial high frequency electric stimulation. Results: Direct cortical stimulation was successful in 73 (85%) patients. Transcranial stimulation was successful in 6 (100%) patients. Transient loss of MEP, which was observed in 16 patients led to transient mild motor deficits in 14 patients. Irreversible loss of MEP led to severe motor deficits in 9 patients. Conclusions: Motor evoked potentials after high frequency repetitive electric transcranial or direct cortical stimulation are a helpful tool during surgical procedures of the central and insular region. In cases of potential loss, they may allow corrective actions before irreversible damage to the motor cortex and the motor pathways.
SOMATOSENSORY EVOKED POTENTIAL (SEP) MONITORING IN CAROTID ENDARTERECTOMY C. Witdoeckt, R. Verhelst, S. Ghariani, G. El Khoury, M. de Tourtchaninoff, R. Dion, J.M. Gu6rit. St-Luc Hospital, Universi~, of
Louvain Medical School, Brussels, Belgium Median nerve SEP monitoring was performed in 205 cases of carotid surgery. The decision to shunt was exclusively based on the SEPs. SEP abnormalities were classified into mild, moderate, and severe alterations, based on the aspect of both the parietal (N20, P27, and P45) and the frontal (N30) components. SEPs remained unchanged in 138 cases (67.3%). Amongst the 67 patients who presented SEP alterations, only 30 patients had to be shunted owing to moderate to severe SEP abnormalities occurring immediately after carotid cross-clamping. In 33 cases SEP abnormalities were reversed by increasing blood pressure (31 cases) or head repositioning (2 cases). Five patients presented alterations of embolic origin (3 of whom were shunted, without any SEP recovery). A shunt was thus used in 16% of cases. SEPs proved extremely sensitive, as none of the non-shunted cases presented long-term neurological sequellae due to intraoperative hemodynamic disturbances. Moreover, our system of semi-qualitative scoring based on mild, moderate, and severe SEP changes proved definitely superior to the classical quantitative criteria for SEP changes based on a more than 1 ms increase of the CCT and/or a more than 50% amplitude decrease of the parietal N20.
329
INTRAOPERATIVE SPINAL MONITORING IN CHILDREN WITH TETHERED SPINAL CORD SYNDROME L. Foggia, M. Colucci, G. Di Manso, G. Giugliano. Neurosurgery
Department, Cardarelli Hospital Napoli, Italy To detect deterioration of spinal cord function and to prevent permanent damages by surgical maneuvers intraoperative monitoring methods have been developed. Our study presents on intraoperative spinal monitoring of ascending and descending pathways in 12 children with tethered spinal cord syndrome (TSCS), evaluated by MRI-spine, previously repaired for low lumbar level myelomeningocele, walked with ankle-foot orthosis, mean age 5.5 (range 3 to 7) years. We recorded both compound muscle action potentials (CMAPs) from the lower limb muscles, using surface electrodes, and the external anal sphincter muscle, using a disposable sphincter electrode (Dantec 13L81), after direct stimulation of roots via two microneurosurgical hoods, placed 1 cm. apart, connected to the electrical stimulator of the EMG machine (Nihon Kodhen), and somatosensory evoked potentials (SEPs) from the parietal scalp after stimulation of the posterior tibial nerve at the ankle. The stimulus was 0.1 ms square wave pulse and intensity less than 20 mA. Muscle relaxants were eliminated during surgery procedures. Both CMAPs and SEPs were monitorated in 12 cases during 3 years. SEPs were not recorded in 3 cases (25%), in which there was an extensive attachment of the spinal cord; in these cases only CMAPs were obtained. Deterioration occurred during 2 operations (16%) with a transitory decrease of amplitude and reproducibility of waveforms: in the first case both SEPs and CMAPs deteriorated, while in the second case only CMAPs deteriorated. No further functional alteration was found after the operations. This study has shown that the intraoperative spinal monitoring can be used as a discriminative instrument for surgery management in children with TSCS and CMAPs provide more sensitive measures of the conventional SEP monitoring.
~--~
SSEPs RESULTS DURING SPINAL DECOMPRESSION FOR METASTATIC TUMORS
W.C. Welch, R.D. Rose. Department of Neurological Surgery and Center for Clinical Neurophysiology, University of Pittsburgh Medical Center, PUH B-400, Pgh PA 15213 USA Intraoperative SSEP monitoring was examined prospectively in 23 patients who underwent surgical resection of metastatic epidural spinal cord tumors. Six patients (26%) underwent tumor embolization prior to resection. All patients had tumor debulking through laminectomy or corpectomy, and most patients received fusion with anterior, posterior or combined instrumentation. SSEPs were monitored prior to incision and through closing. No patient awoke with new neurological deficits in the early post operative period. 52% (n = 12) of patient responses were unchanged. 9% (n = 2; GM, RS) of patient responses improved during surgery. Each awoke with improved neurologic function in the early postoperative period. Fully 39% (9 patients) showed worsened responses during surgery. Specific intraoperative therapies in the patients whose SSEPs worsened included elevating systolic blood pressure, reducing vertebral distraction, repositioning the implant, or delaying further surgical intervention pending correction of physiologic parameters. SSEP monitoring provided the surgical team with reai-time functional data intraoperatively. Monitoring alerted the physicians to potential vertebral overdistraetion, spinal cord compression due to surgical manipulation or hematoma formation, or hemodynamic and metabolic fluctuations. Although all SSEP worsening is not reversible intraoperatively, a subset of patients may benefit from this additional neurophysiologic information.
~'~
FACILITATIONOF MOTOR EVOKED POTENTIALS IN SPINAL CORD MONITORING DURING SPINE SURGERY
G. Andersson, A. Ohlin. Dept. of Clinical Neurophysiology, Lund
University Hospital, Lund, Sweden; Dept. of Orthopaedics, University Hospital Malmii, Sweden Motor evoked potentials (MEPs) on electrical stimulation of the motor cortex were recorded in 26 patients during 28 operations. The cortical stimulus consisted of an anodal pulse, 1500 V, through an electrode at the vertex with a ring of four cathodes approximately 8 cm apart. The MEPs were recorded with surface EMG electrodes placed symmetrically over the bellies of both tibialis anterior muscles. In order to facilitate the responses, a
Poster Session: lntraoperative and Intensive Care Monitonng Procedures
tween the EEG, recorded from healthy persons and patients with neurotoxic diseases. The most informative parameters for diagnozing of hypersthenic neurotoxic syndrome were the 0/3-activities EEG of temporofrontal parts.
rP-~
COMPLEXITY OF STATE SPACE TRAJECTORIES OF MULTICHANNEL EEG MAP SERIES DURING OPEN AND CLOSED EYES
I. Kond~ikor ].2, D. Lehmann i, Jiri Wackermann, T. Kocnig J, T. Yagyu ], K. Kechi i . i The KEY lnstitutefor Brain-Mind Research, University
Hospital of Psychiatry, Zurich, Switzerland; 2 Department of Neurology, University Medical School, P~cs, Hungary; Neuroscience Technology Research, Prague, Czech Republic Series of momentary potential maps of multichannel EEG data can be viewed as trajectories in state space. Topological properties of the shape of the trajectories during different functional states of the brain can be assessed by Global Dimensional Complexity (GDC) and by Global OMEGAComplexity (Omega). Using these two nonrelated methods, we studied 27channel EEG data of 12 healthy subjects under two no-task conditions: eyes closed and open. For both analyses the same artifact-free, 2 sec epochs (256 datapoints) of the band-passed EEG (1.5-32.0 Hz) were analyzed. For each subject the two measures were determined for each epoch (mean 73 epochs/subject, S.D. = 18). GDC as well as Omega increased significantly under the eyes open condition: mean (N = 12) GDC changed from 5.78 to 6.18 (t = 5.91, p 0001), mean Omega from 5.50 to 6.93 (t = 5.10, P 0004). Our results indicate that there are more independent, parallel, functional processes activated during the open eyes state than during the closed eyes state of the brain.
~
CLINICAL AND QUANTITATIVE EEG EVALUATION OF THE EFFICACY OF THE TREATMENT WITH LAMOTRIGINE
V.F. Roman, C.F. Roman. Inst. of Public Health, Targu-Mures, Romania Lamotrigine appears to be an antiepileptic drug with great perspective in the treatment of the complex partial seizures refractory to treatment. Lamotrigine stabilise the neuronal membrane (blocks the calcium and sodium channels) and inhibit the release of the glutamate. We evaluated the efficacy of the treatment with Lamotrigine in 24 patients with partial complex seizures refractory to treatment treated one year with this antiepileptic drug. The efficacy of the treatment has been evaluated by the reduction of number of crisis and by the EEG quantitative changes, using the BEAM (Brain Electrical Activity Mapping). For an exact evaluation of the efficacy of treatment (reduction of number of crisis) was use the response ratio for each cases. For each patient was accomplish the BEAM, initially in the first month, afterwards to 3 months. To all the cases the response ratio shows a reduction of number of crisis over 50%. The BEAM shows a clear influence among secundars foci and the reduction of the activity of dominant foci.
underwent a clinical neurological examination and SEPs on the day before and one week after surgery. We recorded SEPs during the entire course of surgery - at intervals of 3 to 5 minutes immediately before, during and immediately after carotid clamping and at intervals of 10 to 20 minutes during the remaining periods. For each recording, we assessed the latency of the spinal peak N13 and that of the cortical peak N20, in addition we measured the amplitude P15/N20 and N20/P25. Moreover, arterial blood pressure and the course of surgery were closely recorded. The aim of the study is to define critical values of intraoperative SEP changes. Inclusion of patients will be continued until August 31. Detailed data will be presented.
~-~
S. Anton i, E. Castro 2, F. Corral 3 V. Ibarrola i, j. Brasa 2, L. Nombela 2.
I Servicio de lVeurofisiologia, Clinica Puerta de Hierro, Madrid, Spain; 3 Servicio de Neurologia, Clinica Puerta de Hierro, Madrid, Spain; 2 Servicio de Neuroradiologia, Clinica Puerta de Hierro, Madrid, Spain We have studied 79 patients who had EEG monitoring during the implantation of electrical coils in intracranial aneurysms at the Puerta de Hierro Clinic. Patients were sedated and heparinized. A microcatbeter was introduced until the aneurysm was reached. Within the microcatheter, a coil comprising a wire guide of stainless steel and a platinum circular memory at the distal end was introduced inside the aneurysm. A positive electrical current was applied to the proximal end of the guide to induce electrothrombosis at the platinum end and electrolysis at the steel-platinum interface. The procedure is presently indicated as an alternative to surgery when the latter is not feasible. An initial awake EEG was recorded, followed by continuous EEG monitoring during the procedure. Attention was paid to early detection of potential complications: vascular spasm, haemorrhage, coil migration, embolism and tolerance test. Early results from treatment were occasionally observed. Seventy nine patients were studied: 25 men (32%) and 54 women (68%), range: 18-75. Clinical presentation: 80% SAH, 15% mass effect and 5% asymptomatic. Localization: in 5 patients the aneurysm was localized in CA, 10 in Ophtalm art, 4 in Cavernous sinus, 12 in communicating ant art, 7 in MCA, 19 in Communicating post art, 21 in Basilar art, 3 in Posterior cerebral art and 1 in PICA. 30% were in the posterior circulation. The size of the aneurysm was between 0.6 and 3 cm. The number of coils introduced during each session was between 1 and 10, most frequently 2-3. Immediate complications: 4 transitory, 1 definite (death). Late complications: 1 transitory, 1 permanent. We considered that EEG monitoring during coil implantation in intracraneal aneurysms is useful as an objective method to assess the ongoing brain activity and helps the neuroradiologist decide whether to continue or halt the procedure.
~-4-~
Intraoperative and Intensive Care Monitoring Procedures MONITORING OF MEDIAN NERVE SOMATOSENSORY EVOKED POTENTIALS DURING CAROTID SURGERY Ch. Wtiber ], J. Zeitlhofer i, S. Asenbaum 1 L. Claeys z, p. Polterauer 2
] Dept. of Neurology, University of Vienna, Austria; 2 Dept. of Vascular Surge~; University of Vienna, Austria During carotid surgery cerebral blood flow may decrease to a critical level causing remitting or permanent neurological deficits. Clinical examination does not allow to detect these changes during surgery. Therefore, it is essential to provide monitoring techniques which allow an intraoperative assessment of cerebral function. We have used median nerve somatosensory evoked potentials (SEPs) for intraoperative monitoring during carotid surgery. In addition, all patients
NEUROPHYSIOLOGICAL MONITORING IN ENDOVASCULAR TREATMENT OF INTRACRANIAL ANEURYSMS VIA ELECTRICAL COILS
SURGERY OF INTRINSIC LESIONS IN THE MOTOR STRIP: A STEREOTACTICALLY GUIDED MINICRANIOTOMY WITH ELECTROPHYSIOLOGICAL MAPPING OF THE MOTOR CORTEX
W. Eisner i, U. Steude l, K. Bise 2, U.D. Schmid i. 1 Dept. of
Neurosurgery, LMU Munich, Germany; 2 Institute of Neuropathology, LMU Munich, Germany Introduction: Surgery of space occupying lesions that are located subcortically in the central motor area carries a considerable risk of postoperative palsy, We wanted to prove whether a stereotactically guided craniotomy and localisation of the lesion will reduce the incidence of a new postoperative permanent sensorimotor deficit by using electrophysiological mapping of the motor cortex. Material and method: Since April 1992, a series of about 100 patients was operated for tumors that were located in or adjacent to the sensorimotor strip. We routinely used motor cortex mapping using Penfields procedure (5--40 mA, 50Is, 0.2 ms) under general anesthesia without neuromuscular blocking agents. 11 of these patients had their lesion located subcortically, their diameter was < 20 mm. These lesions were operated using additionally a stereotactically guided minicraniotomy of < 30 m m in diameter.
Poster Session: lntraoperative and Intensive Care Monitoring Procedures Results: Based on the intraoperative histological samples and on postoperative MRI/CT, all lesions could be removed completely. All 11 patients had a preoperative motor weakness in at least one contralateral limb, which resolved within 10 days after surgery in all cases. Conclusions: Stereotaxy allows a mini-craniotomy that is hardly larger than the target lesion, thus minimizing surgical exposure of the adjacent cortex. This leads to loss of anatomical landmarks, especially of the topography of the sensorimotor strip, that can be compensated by electrophysiological mapping of the motor cortex, thus enabling the surgeon to define to preserve, the motor cortex during surgery.
[-~-~
MOTOR EVOKED POTENTIAL MONITORING DURING SURGICAL PROCEDURES IN THE CENTRAL AND INSULAR REGION
U. Pechstein, J. Zentner, C. Cedzich, J. Schramm. Department of
Neurosurgery, UniversiO, of Bonn, Germany Introduction: Surgical procedures within the central region and the insular cortex harbor the risk of postoperative motor deficits. We present our experience with motor evoked potential (MEP) monitoring during surgery of supratentorial lesions in the near vicinity of eloquent areas of the brain. Patients and Methods: 91 patients (39 females, 52 males) with a mean age of 47 years (3-78 years), who were operated on lesions of the central and insular region received intraoperative MEP monitoring. After localization of the central sulcus by means of SEP phase reversal, MEP from forearm flexor muscles, thenar and hypothenar were recorded in response to direct cortical high frequency electric stimulation of the motor cortex in 85 patients. 6 patients with tumors of the insular region were monitored with MEP after transcranial high frequency electric stimulation. Results: Direct cortical stimulation was successful in 73 (85%) patients. Transcranial stimulation was successful in 6 (100%) patients. Transient loss of MEP, which was observed in 16 patients led to transient mild motor deficits in 14 patients. Irreversible loss of MEP led to severe motor deficits in 9 patients. Conclusions: Motor evoked potentials after high frequency repetitive electric transcranial or direct cortical stimulation are a helpful tool during surgical procedures of the central and insular region. In cases of potential loss, they may allow corrective actions before irreversible damage to the motor cortex and the motor pathways.
SOMATOSENSORY EVOKED POTENTIAL (SEP) MONITORING IN CAROTID ENDARTERECTOMY C. Witdoeckt, R. Verhelst, S. Ghariani, G. El Khoury, M. de Tourtchaninoff, R. Dion, J.M. Gu6rit. St-Luc Hospital, Universi~, of
Louvain Medical School, Brussels, Belgium Median nerve SEP monitoring was performed in 205 cases of carotid surgery. The decision to shunt was exclusively based on the SEPs. SEP abnormalities were classified into mild, moderate, and severe alterations, based on the aspect of both the parietal (N20, P27, and P45) and the frontal (N30) components. SEPs remained unchanged in 138 cases (67.3%). Amongst the 67 patients who presented SEP alterations, only 30 patients had to be shunted owing to moderate to severe SEP abnormalities occurring immediately after carotid cross-clamping. In 33 cases SEP abnormalities were reversed by increasing blood pressure (31 cases) or head repositioning (2 cases). Five patients presented alterations of embolic origin (3 of whom were shunted, without any SEP recovery). A shunt was thus used in 16% of cases. SEPs proved extremely sensitive, as none of the non-shunted cases presented long-term neurological sequellae due to intraoperative hemodynamic disturbances. Moreover, our system of semi-qualitative scoring based on mild, moderate, and severe SEP changes proved definitely superior to the classical quantitative criteria for SEP changes based on a more than 1 ms increase of the CCT and/or a more than 50% amplitude decrease of the parietal N20.
329
INTRAOPERATIVE SPINAL MONITORING IN CHILDREN WITH TETHERED SPINAL CORD SYNDROME L. Foggia, M. Colucci, G. Di Manso, G. Giugliano. Neurosurgery
Department, Cardarelli Hospital Napoli, Italy To detect deterioration of spinal cord function and to prevent permanent damages by surgical maneuvers intraoperative monitoring methods have been developed. Our study presents on intraoperative spinal monitoring of ascending and descending pathways in 12 children with tethered spinal cord syndrome (TSCS), evaluated by MRI-spine, previously repaired for low lumbar level myelomeningocele, walked with ankle-foot orthosis, mean age 5.5 (range 3 to 7) years. We recorded both compound muscle action potentials (CMAPs) from the lower limb muscles, using surface electrodes, and the external anal sphincter muscle, using a disposable sphincter electrode (Dantec 13L81), after direct stimulation of roots via two microneurosurgical hoods, placed 1 cm. apart, connected to the electrical stimulator of the EMG machine (Nihon Kodhen), and somatosensory evoked potentials (SEPs) from the parietal scalp after stimulation of the posterior tibial nerve at the ankle. The stimulus was 0.1 ms square wave pulse and intensity less than 20 mA. Muscle relaxants were eliminated during surgery procedures. Both CMAPs and SEPs were monitorated in 12 cases during 3 years. SEPs were not recorded in 3 cases (25%), in which there was an extensive attachment of the spinal cord; in these cases only CMAPs were obtained. Deterioration occurred during 2 operations (16%) with a transitory decrease of amplitude and reproducibility of waveforms: in the first case both SEPs and CMAPs deteriorated, while in the second case only CMAPs deteriorated. No further functional alteration was found after the operations. This study has shown that the intraoperative spinal monitoring can be used as a discriminative instrument for surgery management in children with TSCS and CMAPs provide more sensitive measures of the conventional SEP monitoring.
~--~
SSEPs RESULTS DURING SPINAL DECOMPRESSION FOR METASTATIC TUMORS
W.C. Welch, R.D. Rose. Department of Neurological Surgery and Center for Clinical Neurophysiology, University of Pittsburgh Medical Center, PUH B-400, Pgh PA 15213 USA Intraoperative SSEP monitoring was examined prospectively in 23 patients who underwent surgical resection of metastatic epidural spinal cord tumors. Six patients (26%) underwent tumor embolization prior to resection. All patients had tumor debulking through laminectomy or corpectomy, and most patients received fusion with anterior, posterior or combined instrumentation. SSEPs were monitored prior to incision and through closing. No patient awoke with new neurological deficits in the early post operative period. 52% (n = 12) of patient responses were unchanged. 9% (n = 2; GM, RS) of patient responses improved during surgery. Each awoke with improved neurologic function in the early postoperative period. Fully 39% (9 patients) showed worsened responses during surgery. Specific intraoperative therapies in the patients whose SSEPs worsened included elevating systolic blood pressure, reducing vertebral distraction, repositioning the implant, or delaying further surgical intervention pending correction of physiologic parameters. SSEP monitoring provided the surgical team with reai-time functional data intraoperatively. Monitoring alerted the physicians to potential vertebral overdistraetion, spinal cord compression due to surgical manipulation or hematoma formation, or hemodynamic and metabolic fluctuations. Although all SSEP worsening is not reversible intraoperatively, a subset of patients may benefit from this additional neurophysiologic information.
~'~
FACILITATIONOF MOTOR EVOKED POTENTIALS IN SPINAL CORD MONITORING DURING SPINE SURGERY
G. Andersson, A. Ohlin. Dept. of Clinical Neurophysiology, Lund
University Hospital, Lund, Sweden; Dept. of Orthopaedics, University Hospital Malmii, Sweden Motor evoked potentials (MEPs) on electrical stimulation of the motor cortex were recorded in 26 patients during 28 operations. The cortical stimulus consisted of an anodal pulse, 1500 V, through an electrode at the vertex with a ring of four cathodes approximately 8 cm apart. The MEPs were recorded with surface EMG electrodes placed symmetrically over the bellies of both tibialis anterior muscles. In order to facilitate the responses, a