Somatosensory Evoked Potential Monitoring Research Articles

Neurophysiological Monitoring Simulation Using Flash Animation for Anesthesia Resident Training

Surgery of the spine is associated with the possible complication of permanent nerve injury. Neurophysiological monitoring is widely used during spine surgery to decrease the incidence and severity of neurologic injury. A profound understanding of physiological and pharmacological factors influencing evoked potentials is expected from the anesthesia provider. Because demonstration and teaching of all somatosensory evoked potential (SSEP) changes is difficult in the clinical environment, we developed human patient simulator scenarios to facilitate the anesthesia resident training in neurophysiological monitoring. A SSEP simulation for resident training was created using flash animation in a patient simulation program and is the focus of this report. Feedback from participants (anesthesia residents) was obtained by a postscenario survey. This report provides a detailed description of the scenario and computer program. The survey findings indicated that the simulation session is an effective teaching method of SSEP monitoring. Flash animation integration into a patient simulation program for SSEP monitoring appears to be an effective method for anesthesia resident education in neurophysiological monitoring.

A role for motor and somatosensory evoked potentials during anterior cervical discectomy and fusion for patients without myelopathy: Analysis of 57 consecutive cases

Background:Although the usage of combined motor and sensory intraoperative monitoring has been shown to improve the surgical outcome of patients with cervical myelopathy, the role of transcranial electric motor evoked potentials (tceMEP) used in conjunction with somatosensory evoked potentials (SSEP) in patients presenting with radiculopathy but without myelopathy has been less clear.Methods:We retrospectively reviewed all patients (n = 57) with radiculopathy but without myelopathy, undergoing anterior cervical decompression and fusion at a single institution over the past 3 years, who had intraoperative monitoring with both tceMEPs and SSEPs.Results:Fifty-seven (100%) patients presented with radiculopathy, 53 (93.0%) with mechanical neck pain, 35 (61.4%) with motor dysfunction, and 29 (50.9%) with sensory deficits. Intraoperatively, 3 (5.3%) patients experienced decreases in SSEP signal amplitudes and 4 (6.9%) had tceMEP signal changes. There were three instances where a change in neuromonitoring signal required intraoperative alteration of the surgical procedure: these were deemed clinically significant events/true positives. SSEP monitoring showed two false positives and two false negatives, whereas tceMEP monitoring only had one false positive and no false negatives. Thus, tceMEP monitoring exhibited higher sensitivity (33.3% vs. 100%), specificity (95.6% vs. 98.1%), positive predictive value (33.3% vs. 75.0%), negative predictive value (97.7% vs. 100%), and efficiency (91.7% vs. 98.2%) compared to SSEP monitoring alone.Conclusions:Here, we present a retrospective series of 57 patients where tceMEP/SSEP monitoring likely prevented irreversible neurologic damage. Though further prospective studies are needed, there may be a role for combined tceMEP/SSEP monitoring for patients undergoing anterior cervical decompression without myelopathy.

Application of combined monitoring of motor evoked potentials and somatosensory evoked potentials during intramedullary spinal cord tumor operation

Objective To investigate the reliability,superiority and value of combined monitoring of motor evoked potentials(MEP) and somatosensory evoked potentials(SEP) during intramedullary spinal cord tumor surgery under total intravenous anesthesia.Method 72 patients with intramedullary spinal cord tumor were monitored somatosensory evoked potentials and muscle motor evoked potentials during operation.McCormick scale was adopted to evaluate the patients' clinical nerve function.The postoperative to preoperative McCormick grade variation and combimed monitoring of SEP and MEP were compared in this group.Result 14 patients' nerve function was improved.The findings of monitoring were evaluated in 18 patients with depressed McCormick scores.There was significant difference in the latency and amplitude of waves between pretreatment and post-treatment (P＜0.05).The changes of SEP and MEP were correlative with the changes of spinal cord function.Conclusion Combined monitoring of SEP and MEP could help to improve postoperative McCormick scale outcome significantly for patients with intramedullary spinal cord tumor.The waveform of either SEP or MEP might be stable and reliabie in monitoring patients under total intravenous anesthesia.It might be helpful in avoiding 'false negative and/or false positive results'as well as the postoperative neurological sequelae. Key words: Spinal cord; Somatosensory evoked potentials; Motor evoked potentials

Unilateral Cervical Facet Dislocation in a 9-Year-Old Boy

Facet dislocations in children are rare. This article presents the youngest case of a unilateral facet dislocation described in the pediatric population. A 9-year-old boy sustained a flexion/axial loading injury to his cervical spine while wrestling with his friends, causing a unilateral facet dislocation at C4/5. Prereduction magnetic resonance imaging (MRI) demonstrated the absence of a diskal herniation or cord impingement and an intact posterior ligamentous complex. Due to the patient's young age, the decision was made to forgo a supervised awake closed reduction. Closed reduction was performed under general anesthesia with somatosensory-evoked potential and motor-evoked potential monitoring. Closed reduction was successfully achieved after Gardner-Wells tongs were applied and used to manually direct slow, steady in-line traction, along with slight flexion and posterior rotation of the dislocated side under direct fluoroscopy. The patient was immediately awakened from anesthesia and was found to have an intact sensory examination. He was immobilized in a cervical collar for 12 weeks. At 2-year follow-up, he remained asymptomatic without recurrence and had painless full range of motion of the cervical spine. Radiographs revealed a normally aligned cervical spine. Unilateral cervical facet dislocations and subluxations are the result of a distractionflexion force applied to the spine along with a rotational component. These are not uncommon injuries in the adult spine; however, in the young pediatric population, cervical facet dislocations are rare.

Early and long-term results of carotid endarterectomy in diabetic patients

To evaluate results of carotid endarterectomy (CEA) in diabetic patients in a large single-center experience. Over a 13-year period ending in December 2008, 4305 consecutive CEAs in 3573 patients were performed. All patients were prospectively enrolled in a dedicated database. Interventions were performed in diabetic patients in 883 cases (20.5%; group 1) and in nondiabetics in the remaining 3422 (79.5%; group 2). Early results in terms of 30-day stroke and death rates were analyzed and compared. Follow-up results were analyzed with Kaplan-Meier curves and compared with log-rank test. Diabetic patients were more likely to be females and to have coronary artery disease, peripheral arterial disease, hyperlipemia, and arterial hypertension than nondiabetics. There were no differences between the two groups in terms of preoperative clinical status or degree of carotid stenosis. Interventions were performed under general anesthesia with somatosensory-evoked potentials (SEPs) monitoring in 67% of the patients in both groups, while the remaining interventions were performed under clinical monitoring. Shunt insertion (14% and 11%, respectively) and patch closure rates (79% and 76%, respectively) were similar between the two groups. There were no differences between the two groups in terms of neurological outcomes, while the mortality rate was higher in group 1 than in group 2 (P = .002; odds ratio [OR], 3.5; 95% confidence interval [CI], 1.5-8.3); combined 30-day stroke and death rate was significantly higher in group 1 (2%) than in group 2 (0.9%; P = .006; 95% CI, 1.2-3.9; OR, 2.2). At univariate analysis, perioperative risk of stroke and death in diabetic patients was significantly higher in patients undergoing intervention with SEP cerebral monitoring (95% CI, 0.9-39.9; OR, 5.9; P = .01), and this was also confirmed by multivariate analysis (95% CI, 1.1-23.1; OR, 8.3; P = .04). The same analysis in nondiabetics demonstrated that again the need for general anesthesia significantly increased perioperative risk, but this was not significant at multivariate analysis. Follow-up was available in 96% of patients, with a mean duration of 40 months (range, 1-166 months). There were no differences between the two groups in terms of estimated 7-year survival (87.3% and 88.8%, respectively; 95% CI, 0.57-1.08; OR, 0.8) and stroke-free survival (86.8% and 88.1%, respectively; 95% CI, 0.59-1.07; OR, 0.8). Diabetic patients had decreased severe (>70%) restenosis-free survival rates at 7 years than nondiabetics (77.4% and 82.2%, respectively; 95% CI, 0.6-1; OR, 0.8; P = .05). Univariate analysis demonstrated again that the use of instrumental cerebral monitoring significantly decreased stroke-free survival in diabetics (P = .01; log rank, 10.1), and this was also confirmed by multivariate analysis (95% CI, 1.7-17.7; OR, 5.4; P = .005). In our experience, the presence of diabetes mellitus increases three-fold the risk of perioperative death after CEA, while there are no differences with nondiabetics in terms of perioperative stroke. However, the rate of stroke and death at 30 days still remains below the recommended standards. During follow-up, this difference becomes negligible, and results are fairly similar to those obtained in nondiabetics. Particular attention should be paid to patients undergoing intervention under general anesthesia, who seem to represent a subgroup of diabetics at higher perioperative risk, suggesting neurologic monitoring should be used when possible.

Protocol for electrophysiological monitoring of carotid endarterectomies

Abstract Near zero stroke rates can be achieved in carotid endarterectomy (CEA) surgery with selective shunting and electrophysiological neuromonitoring. though false negative rates as high as 40% have been reported. We sought to determine if improved training for interpretation of the monitoring signals can advance the efficacy of selective shunting with electrophysiological monitoring across multiple centers, and determine if other factors could contribute to the differences in reports. Processed and raw beta band (12.5–30 Hz) electroencephalogram (EEG) and median and tibial nerve somatosensory evoked potentials (SSEP) were monitored in 668 CEA cases at six surgical centers. A decrease in amplitude of 50% or more in any EEG or SSEP channel was the criteria for shunting or initiating a neuroprotective protocol. A reduction of 50% or greater in the beta band of the EEG or amplitude of the SSEP was observed in 150 cases. No patient showed signs of a cerebral infarct after surgery. Selective shunting based on EEG and SSEP monitoring can reduce CEA intraoperative stroke rate to a near zero level if trained personnel adopted standardized protocols. We also found that the rapid administration of a protective stroke protocol by attending anesthesiologists was an important aspect of this success rate.

Posterior Rotating Rod Reduction Strategy for Irreducible Atlantoaxial Subluxations With Congenital Odontoid Aplasia

Applying rotating rod techniques to reduce irreducible atlantoaxial dislocation. To spare the occipital-C1 motion by the strategy in reduction of before surgery irreducible atlantoaxial dislocation with obvious neurologic symptoms and congenital odontoid aplasia. The treatment of atlantoaxial dislocation (AAD) is a challenging problem for most surgeons. Posterior surgical stabilization of C1 and C2 include C1-C2 transarticular screws, or C1 lateral with C2 pars screws. These constructs, however, are based on preoperative reductions. When preoperative skull reduction fails and myelopathic symptoms coexist, long-segment cervico-occipital fusion and decompression are usually the only practical choice. The authors explored a different surgical technique to spare the axial occipital joints by rotating rods in polyaxial C1, C3 lateral mass, and C2 pars screws, functioning as a lever analogue. Three before surgery irreducible AAD cases with obvious neurologic symptoms and congenital odontoid aplasia were successfully reduced and fused with this procedure. The authors used intraoperative somatosensory-evoked potential monitoring and intraoperative fluoroscopy. Preoperative skull traction was employed to distract and help extend the atlantoaxial complexes. Three C1-C2 dislocations were reduced completely without any deterioration of neurologic signs. Cervical myelopathic symptoms recovered soon after the operation. No atlantoaxial subluxation recurred. They returned to their normal work and/or activities. The rotating rod strategy is a viable option to reduce and fuse C1-C3 for AAD with odontoid aplasia. It spares the occipital-C1 motion.

Neuromonitoring in Carotid Surgery: Are the Results Obtained in Awake Patients Transferable to Patients Under Sevoflurane/Fentanyl Anesthesia?

Diagnostic accuracy studies of neuromonitoring devices during carotid endarterectomy in awake patients are limited by the question of the transferability to anesthetized patients. This study was designed to compare the different neuromonitoring parameters in patients under regional and general anesthesia with stump pressure as the primary endpoint and the courses of cerebral blood flow velocity (Vmca) measured by transcranial Doppler sonography, regional cerebral oxygen saturation (rSO2) measured by near-infrared spectroscopy, and the amplitude of somatosensory evoked potentials (SEP) as the secondary endpoints. Ninety-six patients undergoing carotid endarterectomy were randomized to regional (n=48) or sevoflurane/fentanyl anesthesia (n=48) group. Absolute and relative changes of Vmca and rSO2 and the SEP amplitude were recorded at baseline, during carotid artery clamping, and after declamping. Intergroup differences (ß) were calculated by generalized estimation equations and linear regression analysis. Mean arterial pressure (P<0.001) and heart rate (P<0.001) were significantly higher in the regional anesthesia group. SP did not differ between both the groups (ß=-1.6; P=0.71). Vmca (ß=9.2; P<0.01) and rSO2 (ß=4.1; P<0.01) values were higher in the awake patients. After adjustment for mean arterial pressure, the differences of Vmca remained consistent (ß=9.3; P<0.01) whereas these of rSO2 during clamping (ß=2.9; P=0.105) and during reperfusion (ß=2.7; P=0.095) disappeared. No significant differences were found for Vmca(%) (ß=-1.0; P=0.80), rSO2(%) (ß=-1.4; P=1.8) and SEP (ß=-2.6; P=0.29). Carotid artery clamping leads to similar results of stump pressure and similar relative changes of transcranial Doppler sonography, near-infrared spectroscopy, and SEP monitoring in patients under regional and sevoflurane/fentanyl anesthesia.

Characterization of Graded Multicenter Animal Spinal Cord Injury Study Contusion Spinal Cord Injury Using Somatosensory-Evoked Potentials

Electrophysiological analysis using somatosensory-evoked potentials (SEPs) and behavioral assessment using Basso, Beattie, Bresnahan (BBB) scale were compared over time for graded Multicenter Animal Spinal Cord Injury Study (MASCIS) contusion spinal cord injury (SCI). To study the SEP responses across different contusion injury severities and to compare them with BBB scores. For any SCI therapy evaluation, it is important to accurately and objectively standardize the injury model. The graded MASCIS contusion injuries on dorsal spine have been standardized using BBB, which is subjective and prone to human errors. Furthermore, dorsal pathway disruption does not always produce locomotor deficits. SEP monitoring provides an advantage of providing a reliable and objective assessment of the functional integrity of dorsal sensory pathways. Four groups of Fischer rats received contusion at T8 using New York University (NYU)-MASCIS impactor from impact heights of 6.25 mm (mild), 12.5 mm (moderate), 25 mm (severe), or 50 mm (very severe). The control group underwent laminectomy only. SEP and BBB recordings were performed once before injury, and then weekly for up to 7 weeks. Graded levels of injury produced concomitant attenuations in hindlimb SEP amplitudes. Following injury, 25 and 50 mm groups together differed significantly from 12.5 and 6.25 mm groups (P < 0.01). From week 5, differences between 12.5 and 6.25 mm groups also became apparent (P < 0.01), which showed significant electrophysiological improvement. However, no significant differences were observed between 25 and 50 mm groups, which showed negligible electrophysiological recovery. Although comparable differences between different groups were also detected by BBB after injury (P < 0.001), BBB was less sensitive in detecting any improvement in 6.25 and 12.5 mm groups. SEP amplitudes and BBB scores decrease corresponding to increase in injury severity, however, these show different temporal patterns of recovery. These results demonstrate the utility of SEPs in conjunction with BBB, to monitor therapeutic interventions in SCI research.

Role of motor-evoked potential monitoring in conjunction with temporary clipping of spinal nerve roots in posterior thoracic spine tumor surgery

Background context The vascular supply of the thoracic spinal cord depends on the thoracolumbar segmental arteries. Because of the small size and ventral course of these arteries in relation to the dorsal root ganglion and ventral root, they cannot be reliably identified during surgery by anatomic or morphologic criteria. Sacrificing them will most likely result in paraplegia. Purpose The goal of this study was to evaluate a novel method of intraoperative testing of a nerve root's contribution to the blood supply of the thoracic spinal cord. Study design/setting This is a clinical retrospective study of 49 patients diagnosed with thoracic spine tumors. Temporary nerve root clipping combined with motor-evoked potential (MEP) and somatosensory-evoked potential (SSEP) monitoring was performed; additionally, postoperative clinical evaluation was done and reported in all cases. Methods All cases were monitored by SSEP and MEPs. The nerve root to be sacrificed was temporarily clipped using standard aneurysm clips, and SSEP/MEP were assessed before and after clipping. Four nerve roots were sacrificed in four cases, three nerve roots in eight cases, and two nerve roots in 22 cases. Nerve roots were sacrificed bilaterally in 12 cases. Results Most patients (47/49) had no changes in MEP/SSEP and had no neurological deficit postoperatively. One case of a spinal sarcoma demonstrated changes in MEP after temporary clipping of the left T11 nerve root. The nerve was not sacrificed, and the patient was neurologically intact after surgery. In another case of a sarcoma, MEPs changed in the lower limbs after ligation of left T9 nerve root. It was felt that it was a global event because of anesthesia. Postoperatively, the patient had complete paraplegia but recovered almost completely after 6 months. Conclusions Temporary nerve root clipping combined with MEP and SSEP monitoring may enhance the impact of neuromonitoring in the intraoperative management of patients with thoracic spine tumors and favorably influence neurological outcome.

Evaluation of the role of combined TES-MEP and CSEP monitoring during the spinal surgery

To evaluate of the role of transcranial electrical stimulation motor evoked potential (TES-MEP) in combination with cortical somatosensory evoked potential (CSEP) monitoring during the spinal surgery. TES-MEP on bilateral anterior tibial muscle and flexor hallucal brevis and CSEP on bilateral posterior tibial nerve were observed simultaneously on 293 patients during spinal surgery from July 2006 to April 2009. Intravenous anesthesia was employed in all the patients, a part of which were added low dose of sevoflurane or muscle relaxant. The results of TES-MEP, CSEP and combined monitoring were analyzed statistically. Pre-operative and post-operative motor and sensory functions of spinal cord were compared. Success rate of TES-MEP, CSEP and combined monitoring was 90.8%, 96.9% and 100% respectively. For the judgment of motor function of spinal cord, the sensitivity of TES-MEP and CSEP was 100% and 89.3% respectively and the specificity of 98.4% and 96.9%. The Youden index of the two methods was 0.984 and 0.862. For sensory function, the sensitivity of them was 76.7% and 93.3% respectively and the specificity of 98.7% and 98.0%. The Youden index was 0.754 and 0.913. The sensitivity of combined monitoring was 100%, with the specificity of 96.9%. The Youden index was 0.969. The precision of monitoring motor function of spinal cord with TES-MEP is higher than that with CSEP, however, for sensory function, CSEP is more precise. The sensitivity and precision of combined monitoring for spinal cord function were apparently better than that of unitary TES-MEP or CSEP. The combined TES-MEP and CSEP monitoring is a relatively ideal method.

Somatosensory evoked potential monitoring of the brachial plexus during a woodward procedure for correction of Sprengel's deformity

Sprengel's deformity is the most common congenital deformity of the shoulder. A known complication of correcting this deformity is brachial plexus palsy. In this study we used somatosensory evoked potential (SSEP) monitoring during correction of a Sprengel's deformity and identified an early iatrogenic brachial plexus injury. The operation was modified, and permanent nerve injury was avoided. We recommend that SSEP monitoring be considered in procedures to correct Sprengel's deformity.

Alternative anterior reference sites for measuring posterior tibial nerve somatosensory evoked potentials

The purpose of this study was to examine the utility and feasibility of using alternative anterior reference leads when measuring left posterior tibial nerve somatosensory evoked potentials (SEPs). With IRB approval, 12 patients were monitored using both traditional (FPz and C4') and alternative anterior (F3 and F4) reference leads during routine spine surgery with SEP monitoring. Recordings from the routine and novel electrode pairs were collected and analyzed. All of the SEP amplitudes measured were of similar magnitude except for that of F3-F4, which was significantly lower (P < 0.001) than all of the other five lead combinations which were assessed (Cz'-FPz, C3'-C4', C3'-F4, Cz'-F3, and Cz'-F4). The latencies of the novel lead combinations (C3'-F4, Cz'-F3, Cz'-F4, and F3-F4) were similar to those of the "gold standards" (Cz'-FPz and C3'-C4') (pooled median, 45.6 ms with 25-75th percentiles, 44.0-47.8 ms, P = 0.308). The coefficients of variation (CV %) of the amplitudes were not statistically significantly different (P = 0.341). The use of alternative frontal reference leads (F3 and F4) for left posterior tibial nerve SEP monitoring yields signals of equal quality and reproducibility compared to signals with standard (FPz and C4') referencing. These alternative leads may substitute for traditional referencing when placement of FPz or C4' is precluded by the location of surgery.

Significance and cost-effectiveness of somatosensory evoked potential monitoring in cervical spine surgery

Intraoperative somatosensory evoked potential (SSEP) monitoring during cervical spine surgery is not a universally accepted standard of care. Our retrospective study evaluated the efficacy and cost-effectiveness of intraoperative SSEP in a single surgeon's practice. Intraoperative SSEP monitoring was performed on 210 consecutive patients who had cervical spine surgery: anterior cervical approach 140 and posterior approach 70. They were screened for degradation or loss of SSEP data. A cost analysis included annual medical costs for health and human services, durable goods and expendable commodities. Temporary loss of the electrical wave during cauterization resolved upon discontinuation of the cautery. We had no loss of cortical wave with preservation of the popliteal potential. A drop in the amplitude of the cortical wave was observed in three patients. This drop was resolved after hemodynamic stabilization in the first patient, readjusting the bone graft in the second patient, and interrupting the surgery in the third patient. The additional cost for SSEP monitoring was $835 per case and the total cost of the surgery was $13,835 per case. By spending $31,546 per year on SSEP, our institution is saving a total cost ranging from $64,074 to $102,192 per patient injured per year. Intraoperative SSEP monitoring is a reliable and cost-effective method for preventing postoperative neurological deficit by the early detection of vascular or mechanical compromise, and the immediate alteration of the anesthetic or surgical technique.

Quantifying the effect of isoflurane and nitrous oxide on somatosensory-evoked potentials

Anaesthetic techniques may have a significant effect on intraoperative-evoked potentials (EP). The present study is designed to compare Propofol anaesthesia with Isoflurane (with or without nitrous oxide) during intraoperative somatosensory-evoked potential (SSEP) monitoring in 15 ASA Grade I and II patients undergoing surgery for intracranial tumours. SSEPs in response to median and posterior tibial nerve stimulation were recorded under four different anaesthetic conditions: 1) Propofol infusion and ventilation with air-oxygen, 2) Isoflurane, 1.0 MAC and ventilation with air-oxygen, 3) Isoflurane 1.0 MAC and ventilation with nitrous oxide-oxygen, and 4) Return to Isoflurane, 1.0 MAC and ventilation with air-oxygen. Intraoperative monitoring of somatosensory evoked potentials is best recordable using Propofol. The morphology of the EP is reproducible with Isoflurane. This effect is exaggerated when it is advisable to avoid nitrous oxide.

Evoked Potential Monitoring Identifies Possible Neurological Injury During Positioning for Craniotomy

Somatosensory-evoked potential (SSEP) monitoring is commonly used to detect changes in nerve conduction and prevent impending nerve injury. We present a case series of two patients who had SSEP monitoring for their surgical craniotomy procedure, and who, upon positioning supine with their head tilted 30 degrees-45 degrees, developed unilateral upper extremity SSEP changes. These SSEP changes were reversed when the patients were repositioned. These cases indicate the clinical usefulness of monitoring SSEPs while positioning the patient and adjusting position accordingly to prevent injury.

Therapeutic extradural cortical stimulation for Parkinson's Disease: Report of six cases and review of the literature

Objectives We report our experience and results with extradural cortical stimulation (ECS) in the surgical treatment of Parkinson's Disease (PD). Besides, we review the literature supporting the use of this technique. Materials and methods Six patients with advanced PD and exclusion criteria for Deep Brain Stimulation (DBS) were included in our ECS protocol. With the aid of functional MRI and somato-sensory evoked potentials monitoring, the motor cortex projection over the scalp was drawn. Finally, under local anesthesia a stimulation lead was placed in the epidural space overlying the central sulcus. Results Patients showed mild daily life activities improvement with a slightly lower levodopa equivalent dose, but UPDRS part III scores showed no significant modification. Conclusions Despite ECS is a minimally invasive surgical technique, our results only support its use in selected patients with advanced PD, in whom this therapy may be modestly effective. More experimental studies regarding the neuromodulation of the basal ganglia-cortex loops are required to optimize its clinical application.

Monitoring of Spinal Cord Functional Status in Patients with Intramedullary Tumors

Objective. To analyze disorders in spinal cord function in patients with intramedullary tumors (IMT) and to ascertain informative value of intraoperative monitoring of somatosensory evoked potentials (SSEPs) for prevention of neurological complications during tumor removal using infrared laser irradiation. Material and Methods. SSEPs were recorded from upper and/or lower extremity nerve stimulation in 38 patients with IMT of different localization before surgery, during operation, at 14 to 28 days after surgery, and at long-term follow-up period. The nature and the rate of spinal cord conduction abnormality depending on the tumor localization and volume were analyzed. Results. Postoperative examination showed a positive dynamics of SSEP parameters in 14.0 % of patients, and the absence of significant changes – in 65.6 %. It was found that SSEP responses can reflect short-term effects of surgical manipulations before a direct tumor removal, and of arterial pressure. Long-lasting anesthesia progressively increases SSEP delay time. These factors are taken into account in determining a threshold for functional permissibility of intervention at the stage of tumor removal and at the final stage when laser radiation is applied. Changes were assessed by comparison with parameters obtained just before a given stage. Conclusion. Monitoring of SSEPs at main stages of surgery allowed avoiding additional traumatization of the spinal cord, performing total removal of the tumor, preventing its continuous growth, and achieving of good long-term clinical results of the treatment.

Intramedullary cavernous malformations: Clinical features and surgical technique via hemilaminectomy

Objective The purpose of this study was to define the clinical features and the surgical technique of unilateral hemilaminectomy for treating intramedullary cavernous malformations. Materials and methods Retrospective chart was performed in 16 patients with histologically diagnosed intramedullary cavernous malformations. All patients were treated with unilateral hemilaminectomy and microsurgical resection of the malformations. The pre- and postoperative neurological state was evaluated using Frankel scale. Results There were nine females and seven males (mean age 38 years) harbouring symptomatic intramedullary cavernous malformations. The annual retrospective haemorrhage rate was 3.1% per patient/year. All cavernous malformations were completely resected. Twelve of 16 patients experienced the improvement of the neurological state and in four patients, clinical features remained unchanged during the follow-up period. Static and dynamic plain radiograph film showed none of them had spinal deformity or spinal instability. Conclusion According to the defined bleeding risk, symptomatic and MRI-morphologically growing intramedullary cavernous malformations should be totally surgically removed, to avoid the recurrence and rebleeding of the residue. A least traumatic myelotomy, as well as a meticulous microsurgical technique and the intraoperative somatosensory evoked potentials monitoring, together with selection of a minimally invasive microsurgical approach (hemilaminectomy), leads to a favourable outcome and prevents additional morbidity.

Combined motor- and somatosensory-evoked potential monitoring for spine and spinal cord surgery: correlation of clinical and neurophysiological data in 85 consecutive procedures

Prospective study. The primary objective of neurophysiological monitoring during surgery is to prevent permanent neurological sequelae. To avoid neurological injury, we applied somatosensory-evoked potentials (SEPs) and/or motor-evoked potentials (MEPs). We evaluated whether the combination of SEP and MEP for spinal surgery may be beneficial. Asian Medical Center, University of Ulsan College of Medicine, Seoul, Korea. Combined SEP/MEP monitoring was attempted in 100 consecutive procedures for spinal operations. Trains of transcranial electrical stimulation over the motor cortex were used to elicit MEPs from the muscles of the upper/lower limbs. The tibial and median nerves were stimulated to record SEP. Combined SEP/MEP recording was successfully achieved in 85 of 100 operations. In 61 of 85 operations (71%), SEP and MEP were stable, and all patients remained neurologically intact after surgery. Significant MEP changes were recorded in 20 operations, either combined with (n=4) or without (n=16) SEP changes. In 7 of these 20 operations, MEP recovered to some extent after surgical intervention, and these patients showed no neurological changes. In the remaining 13 operations, MEP did not recover and the patients had a transient (n=4) or a permanent (n=3) motor deficit. Significant SEP changes with stable MEP were observed in four operations, all of which were not related to postoperative motor deficit. Combined SEP/MEP monitoring provided higher sensitivity and higher positive/negative predictive value than single-modality monitoring techniques. Detection of MEP changes and adjustment of surgical strategy may prevent irreversible pyramidal tract damage.