Results: We will show several neurophysiological pictures, tryingto correlate the findings to the etiology of suffering, laying the foun-dations for the solution of the problem as possible.

Conclusion: From our experience in the last 15 years, we were ableto finalize selection of patients, a method of surgical approach andthe neurophysiological monitoring system to enable us to preservethe hearing level socially useful in 52.6% of patients (case studiesof recent 7 years of 113 patients). Particular attention is placed onthe indication for intervention and the selection of patients withan adequate preoperative study.

doi:10.1016/j.clinph.2013.12.024

22. Implementation of multimodal intraoperative neuromoni-toring into an established setting of awake craniotomy—AndreaSzelényi, Samis Zella, Marion Rapp, Maria Smuga, Hans-JakobSteiger, Michael Sabel (Neurosurgical Clinic, University Hospital,Duesseldorf, Germany)

Introduction: Bipolar 60 Hz-stimulation-mapping and clinicalevaluation are commonly used for patient assessment in awake neu-rosurgical procedures. Stimulation related seizures, afterdischarges,delayed wake-up or malcompliance interfere with successful testing.Somatosensory (SEPs) and motor evoked potentials (MEPs) areobjective tools for mapping and monitoring independent of patients’compliance. Their introduction into an established ‘awake setting’were prospectively analysed for feasibility, reliability and effect onsurgical strategy.

Materials and methods: Multimodal intraoperative neuromonitor-ing consisting of contralateral SEPs, transcranially (TES) and directcortically (DCS) elicited MEPs (monopolar, train-of-five-techniquewith 250 Hz) were implemented in a 13 month period.

Results: 105 patients (53 � 14 years, 60 male) with frontal/precen-tral (48), postcentral/parietal (33), temporal (16) and trigonal (8)located lesions (glioma (81), metastasis (18), others (6)) were ana-lysed. SEPs and TES-MEPs were present in all 105 patients, as wellas DCS for cortical and subcortical motor mapping. There were noserious side effects despite the description of tingling pain duringdirect cortical stimulation. After 5 months, a bias towards motormapping with the monopolar stimulation was seen, such monopolarvs. bipolar stimulation was only compared in the first 70 patients:DCS-MEPs were elicited in all 70 patients, whereas the 60 Hz-stimu-lation elicited motor responses in 60/70 patients (p = 0.0016; Fish-er’~s-test). 90/105 patients (86%) were cooperative for the awakesetting. In 4 of the 15 remaining patients (4%) language testingwas considered essential and surgery was prematurely terminated.In the other 11 patients (10%), surgery was continued asleep withmonopolar cortical and subcortical mapping and continuous moni-toring of SEPs and MEPs.

Discussion: Multimodal monitoring is feasible in awake cranioto-mies and was well tolerated. Despite malcompliance and clinicaldeterioration it allows for objective assessment of somatosensoryand motor pathways and proceeding with the surgical tumour resec-tion. In conclusion, the inclusion of multimodal monitoring might beessential for pericentral surgery.

doi:10.1016/j.clinph.2013.12.025

23. Are persistent changes in SEPs and MEPs sensitive for pre-dicting postoperative limb motor deficit during cerebral aneu-rysm surgery?—Lanjun Guo, Wilson Cui, Francis Wolf, MichaelLawton, Adrian Gelb (University of California, San Francisco,United States)

Introduction: Motor evoked potentials (MEPs) can be used as anadjunct to somatosensory evoked potentials (SEPs) to identify brainischemia during surgical treatment of cerebral aneurysms. Persistentchanges (failure to return to baseline by end of surgery) can be usedto predict postoperative deficit. The sensitivity, specificity, positiveand negative predictive value of persistent changes in SEPs/MEPsfor predicting neurologic deficit is still being defined. In a separatestudy, the sensitivity of persistent changes in SEPs for predictingnew limb paresis was 13%, and MEPs was 32%. In this study we eval-uated those patients with new postoperative motor deficits to deter-mine the reason for the low sensitivity.

Material and methods: This was a retrospective study based on 446cerebral aneurysm patients who underwent clipping at our institu-tion from 2009–2011. Twenty-eight patients with new postoperativemotor deficits were identified. The neuromonitoring reports andmedical records were reviewed in more detail in these patients.

Results: In the 28 patients, ten patients (36%, sensitivity) were pre-dicted by persistent SEPs/MEPs changes. In the 18 patients whosedeficits were not predicted, five patients (18%) had delayed deficits;eight (29%) had mild temporary motor deficits; in two patients (7%),monitoring was stopped less than ten minutes after aneurysms wereclipped; in one patient (3.6%), no reliable SEPs were recorded on thesurgery side at baseline. If the last three cases are eliminated, thesensitivity of predicting for all deficit at time when patient wakeup is 50% (10/20 patients); to severe and persistent motor deficitis 83% (10/12 patients).

Conclusion: This study demonstrates that the reason for the lowsensitivity of SEPs/MEPs is that these methods are not sensitive todelayed and/or mild temporary deficits. However, the study alsoshows that SEPs/MEPs have better predictability in cases of severeand persistent postoperative limb paresis.

doi:10.1016/j.clinph.2013.12.026

24. Neurophysiologic mechanism of isoflurane influence to theparameters of the D wave—Anna Maria Nuti a, Vedran Deletis b

(a Sant’andrea hospital, University La sapienza, Rome, Italy, b St.Luke’s Roosevelt Hospital, Intraoperative Neurophysiology, NY,United States)

Introduction: It has been accepted that Isoflurane influences gen-eration of the I waves by blocking synapses within the motor cortex.Contrary to that, the mechanism of Isoflurane influence on theamplitude and latency of the D wave is not completely understood.It has been proposed that its influence on the D wave is by depres-sion of Na+ currents at the nodes of Ranvier of the corticospinal(CT) axons. We proposed a hypothesis that the Isofluorane influenceon the parameters of the D wave is by its cerebral vasodilatatoryeffect, causing a shunt of stimulating current applied to the skull,forcing it to flow more superficially.

Patients and methods: Five patients with no neurological deficitswere studied: three underwent surgery of the conus/cauda andtwo underwent supratentorial procedures. Anaesthesia was main-tained with Propofol and Fentanyl, and by the end of surgery, Isoflu-rane was added up to 2% endtidal concentration. D waves wereelicited by transcranial electrical stimulation (TES), (CZ anode vs.6 cm in front, cathode), while epidural recordings of the D waveswere done at the low thoracic spinal cord, after myelotomy. Patientswho underwent craniotomy saw percutaneous placement of an epi-dural electrode in the low thoracic spinal cord, while stimulationwas performed via strip electrode placed over M1 for the leg.

Results: When the D wave was elicited by TES using up to 2% ofIsoflurane, it correlated with a decrement of the D wave amplitudeabout 50% and latencies prolongation about 0.5 ms. Surprisingly,

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when the D wave was elicited by direct exposed cortex stimulation,Isoflurane did not change either its amplitude or latencies.

Conclusion: Presented data provide evidence against the hypothe-sis of Isoflurane influence on the CT axons membrane properties, butsupports the hypothesis of its influence on the biophysics of TES.

doi:10.1016/j.clinph.2013.12.027

25. Continuous dynamic mapping of the corticospinal tract dur-ing surgery of motor eloquent brain tumours—Kathleen Seidel,Juergen Beck, Philippe Schucht, Andreas Raabe (Department ofNeurosurgery, Inselspital, Bern University Hospital, Switzerland)

Introduction: The objective was to establish a mapping techniqueto overcome the temporal and spatial limitations of classical subcor-tical mapping of the corticospinal tract (CST). The feasibility andsafety of continuous subcortical mapping synchronized with tissueresection was evaluated.

Methods: This prospective study included 69 patients who under-went tumour surgery adjacent to the CST (<1 cm using diffusion ten-sion imaging and fiber tracking) with simultaneous subcorticalmonopolar mapping (short train of 5 cathodal stimuli, inter-stimulusinterval 4.0 ms, pulse duration 0.5 ms) and an acoustic motor evokedpotential alarm. Continuous (temporal coverage) and dynamic (spa-tial coverage) mapping was technically realized by integrating themapping probe at the tip of a suction device with the concept thatthis device will be in contact with the tissue where the resection isperformed. Motor function was assessed one day after surgery, atdischarge, and at 3 months.

Results: All procedures were technically successful. There was a1:1 correlation of motor thresholds (MTs) for stimulation sitessimultaneously mapped with the new suction mapping device andthe classic fingerstick probe (24 patients, 74 stimulation points,r = 0.996, p < 0.001). Lowest individual MTs were as follows (MT,number of patients): >20 mA, n = 7; 11–20 mA, n = 13; 6–10 mA,n = 8; 4–5 mA, n = 17; 1–3 mA, n = 24. At 3 months, two patients(3%) had a persisting postoperative motor deficit, both of which werecaused by a vascular injury. No patient had a permanent motor def-icit caused by a mechanical injury of the CST.

Conclusion: Continuous dynamic mapping was found to be a feasi-ble and ergonomic technique for localizing the CST. The acousticfeedback and the ability to continuously stimulate the tissue exactlyat the site of tissue removal might improve the accuracy of mapping,especially at low stimulation intensities. This technique mayincrease the safety of motor eloquent tumour surgery.

doi:10.1016/j.clinph.2013.12.028

26. High intensity transcranial electrical stimulation: Brainstemfugal motor tracts may augment epidural D-waves of the cortico-spinal system—Henricus Journee a, Marc Dijk van a, HannekeBerends b, Pierre Robe a, Rob Groen a (a UMCG, The Netherlands,b Sint Maartenskliniek, The Netherlands)

Introduction: At increasing intensities of transcranial electricalstimulation (TES) the cortico-spinal tract will depolarize deeper inthe brain down to the foramen magnum, possibly causing otherspine bounded tracts originating from the brainstem to depolarizetoo. It is hypothesized that the threshold to activate these parapyra-midal (PP) axons is higher than the subcortical motor threshold ofaxons of the corticospinal tract (CT). In addition, one may expect thataction potentials of PP axons join d-waves of the CT and augmenttheir amplitudes.

Methods: A cohort of 19 patients (11 female; age mean:51.3 � 14y) with surgical procedures in the spinal canal under intra-operative neuromonitoring were included. TES was performed usingC3 and C4 stimulation with constant voltage at 100 or 200 mcs pulsewidth. D-waves were measured caudal or rostral from the cordlesions. Muscular motor evoked potentials (mMEPs) were takenfrom the abductors pollicis brevis (APB) at cervical epidural record-ing levels or otherwise the anterior tibialis (AT). Voltage motorthreshold parameters were derived for d-waves at subcortical level(Vthd1), at brainstem level at a latency jump of around �0.8 ms(Vthd2) and for mMEPs (VthAPB, and VthAT). The threshold ratioTRd1d2 equals Vthd2/ Vthd1. ARd1d2 is the supramaximal ampli-tude ratio of d1 and d2 waves.

Results: TRd1d2, ARd1d2, d1 and mMEP threshold values are listedbelow. TRd1d2 ARd1d2 Cervical level Other spinal levels Vthd1VthAPB Vthd1 VthAT N 19 13 8 8 11 11 mean�SD 3.09�0.742.26�0.53 31.9�7.8 V 33.4�7.4 V 61.8�40.1 V 70.0�48.6 V Paireddifferences Mean�SD �1.5 � 2.7 V �8.2 � 16.8 V No significant dif-ferences (P = 0.05) between d1 and mMEP thresholds were found.d2 amplitudes may double or triple d1 amplitudes, whereas themean TRd1d2 is 3.1.

Conclusions: At TES intensities over 3� threshold, parapyramidalaxons apparently increase d-wave amplitudes and do not exclusivelyrepresent the corticospinal tract function.

doi:10.1016/j.clinph.2013.12.029

27. Facial nerve palsy after vestibular schwannoma surgery:Dynamic risk-stratification based on continuous EMG-monitor-ing—Julian Prell, Christian Strauss, Stefan Rampp (Martin-Luther-Univeristät Halle-Wittenberg, Neurosurgery, Germany)

Introduction: A-trains are a pathological pattern in intraoperativeEMG-monitoring. Traintime, a parameter calculated by automatedEMG-analysis, quantifies A-train activity. Its extent is associatedwith the degree of postoperative facial nerve palsy. However, falsepositive results have been observed. A systematic flaw in automatedanalysis was hypothesized.

Material and methods: Facial nerve EMG-data from 79 patientsundergoing vestibular schwannoma surgery were analysed visually.Automated traintime was compared with these results. The progres-sive risk for postoperative paresis was calculated with respect totraintime (visual and automated).

Results: Automated analysis identified a small (1.46%), but highlyrepresentative fraction of overall A-train activity: Pearson’s correla-tion coefficient between both values was 0.944 (p < 0.001). Bothwere correlated with clinical outcome in a highly significant way(p < 0.001) with Spearman Rho 0.592 (automated) and 0.563(visual). Progressive risk development was visualized as an inversesigmoid curve with traintime on a logarithmic scale. After an initialsteep rise in the curve, a short plateau (�15% risk) is reached. Thischanges to a shallow slope with constantly rising risk, which is then(at �50% risk) followed by a steep rise again, quickly reaching 100%of relative risk. With the ratio of 0.0146 between mean automatedan visual traintime factored in, the risk-curves for both measuresare basically identical concerning form and dimension.

Conclusion: Automated traintime is a representative and reliableexpression for overall A-train activity. Rigid thresholds are problem-atic, as they are either set too high or too low and do not reflect thecomplexity of risk-development. Individual risk for postoperativepalsy can be estimated on the basis of the calculated curve presented.

doi:10.1016/j.clinph.2013.12.030

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