Psychological factors and long-term tinnitus handicap in vestibular schwannoma patients after retrosigmoid microsurgery - a cross-sectional study.

OBJECTIVE: This study aimed to investigate the connection between psychological factors and postoperative tinnitus in vestibular schwannoma (VS) patients following retrosigmoid microsurgery. DESIGN: Cross-sectional study. STUDY SAMPLE: Ninety-three VS patients participated, completing questionnaires on demographics, tinnitus severity (THI-12), personality traits (TIPI-G), dizziness impact (DHI), perceived health benefits (GBI), somatisation tendencies (SOMS-2), and psychological distress (HADS-D). Our analysis involved Mann-Whitney U-tests, Spearman's rank-order correlations, and false discovery rate correction. RESULTS: Most participants reported postoperative tinnitus (77/93), with 41 experiencing it preoperatively. Emotional stability correlated negatively with tinnitus presence, while tinnitus severity was associated with emotional distress. Preoperative somatisation tendencies were also positively linked to tinnitus severity. Postoperative Tinnitus was further linked to reduced perceived health benefits and increased anxiety and depression levels. Notably, age and gender showed no significant associations. CONCLUSION: This study uncovers the interplay between postoperative tinnitus and psychological factors in VS patients, highlighting emotional and cognitive dimensions. Tailored psychological interventions addressing tinnitus's psychosomatic impact may enhance patients quality of life.

A novel method for calibrating head models to account for variability in conductivity and its evaluation in a sphere model.

The accuracy in electroencephalography (EEG) and combined EEG and magnetoencephalography (MEG) source reconstructions as well as in optimized transcranial electric stimulation (TES) depends on the conductive properties assigned to the head model, and most importantly on individual skull conductivity. In this study, we present an automatic pipeline to calibrate head models with respect to skull conductivity based on the reconstruction of the P20/N20 response using somatosensory evoked potentials and fields. In order to validate in a well-controlled setup without interplay with numerical errors, we evaluate the accuracy of this algorithm in a 4-layer spherical head model using realistic noise levels as well as dipole sources at different eccentricities with strengths and orientations related to somatosensory experiments. Our results show that the reference skull conductivity can be reliably reconstructed for sources resembling the generator of the P20/N20 response. In case of erroneous assumptions on scalp conductivity, the resulting skull conductivity parameter counterbalances this effect, so that EEG source reconstructions using the fitted skull conductivity parameter result in lower errors than when using the standard value. We propose an automatized procedure to calibrate head models which only relies on non-invasive modalities that are available in a standard MEG laboratory, measures under in vivo conditions and in the low frequency range of interest. Calibrated head modeling can improve EEG and combined EEG/MEG source analysis as well as optimized TES.

Zoomed MRI Guided by Combined EEG/MEG Source Analysis: A Multimodal Approach for Optimizing Presurgical Epilepsy Work-up and its Application in a Multi-focal Epilepsy Patient Case Study.

In recent years, the use of source analysis based on electroencephalography (EEG) and magnetoencephalography (MEG) has gained considerable attention in presurgical epilepsy diagnosis. However, in many cases the source analysis alone is not used to tailor surgery unless the findings are confirmed by lesions, such as, e.g., cortical malformations in MRI. For many patients, the histology of tissue resected from MRI negative epilepsy shows small lesions, which indicates the need for more sensitive MR sequences. In this paper, we describe a technique to maximize the synergy between combined EEG/MEG (EMEG) source analysis and high resolution MRI. The procedure has three main steps: (1) construction of a detailed and calibrated finite element head model that considers the variation of individual skull conductivities and white matter anisotropy, (2) EMEG source analysis performed on averaged interictal epileptic discharges (IED), (3) high resolution (0.5 mm) zoomed MR imaging, limited to small areas centered at the EMEG source locations. The proposed new diagnosis procedure was then applied in a particularly challenging case of an epilepsy patient: EMEG analysis at the peak of the IED coincided with a right frontal focal cortical dysplasia (FCD), which had been detected at standard 1 mm resolution MRI. Of higher interest, zoomed MR imaging (applying parallel transmission, 'ZOOMit') guided by EMEG at the spike onset revealed a second, fairly subtle, FCD in the left fronto-central region. The evaluation revealed that this second FCD, which had not been detectable with standard 1 mm resolution, was the trigger of the seizures.

[Intraoperative monitoring of the facial nerve : Vestibular schwannoma surgery]. / Intraoperative Funktionsüberwachung des N. facialis : Operationen an Vestibularisschwannomen.

BACKGROUND: In vestibular schwannoma surgery, facial nerve injury with consecutive functional impairment is one of the most important complications. Intraoperative monitoring of facial nerve function has been developed in order to avoid this complication. OBJECTIVE: Which methods for intraoperative monitoring have been developed? Which methods are in use today and what can they achieve in modern vestibular schwannoma surgery? MATERIAL AND METHODS: This article provides an evaluation and summary of the literature, as well as a discussion of the methods and their ability to achieve the goals of intraoperative monitoring. RESULTS: Intraoperative functional monitoring aims to identify and map the facial nerve in the surgical field during surgery. It also aims to identify potentially damaging events and allow for intraoperative prognosis of functional outcome. Available methods are direct electrical stimulation, free-running electromyogram (EMG), facial nerve evoked potentials, and processed EMG. CONCLUSION: Identification and mapping of the facial nerve in the surgical field can be reliably achieved by direct electrical stimulation; potentially dangerous events can be identified in real time by the free-running EMG and the processed EMG, and almost in real time by facial nerve evoked potentials. Intraoperative prognostics are hampered by false-positive results with all available methods and have limited reliability.

[Intraoperative monitoring of cochlear nerve function during cerebello-pontine angle surgery]. / Intraoperatives Monitoring des N. cochlearis bei Eingriffen im Kleinhirnbrückenwinkel.

BACKGROUND: Surgical procedures in the cerebello-pontine angle (CPA), e. g. for vestibular schwannoma, have an increased risk for damage to the cochlear nerve. Consequently, hearing deterioration up to complete deafness may result with severe impact on quality of life. Methods for intraoperative monitoring of function may minimize such risks. OBJECTIVE: Review of current methods for intraoperative monitoring of the cochelar nerve and summary of new developments. MATERIALS AND METHODS: Analysis and summary of literature, discussion of new methods. RESULTS: Early auditory evoked potentials using click stimuli remain the standard method for intraoperative monitoring of cochlear nerve function. Amplitude and latency changes indicate a risk of postoperative hearing deterioration; however demonstrate only limited further differentiation of hearing quality. As novel methods, near-field recordings may allow faster feedback and auditory steady state responses potentially enable frequency specific testing. CONCLUSIONS: Intraoperative monitoring of the cochlear nerve is an integral component of CPA surgery. It enables detection of potential nerve damage and thus contributes to avoiding postoperative functional deficits. Development and implementation of novel and additional approaches may further improve its clinical value.

Early prediction of delayed cerebral ischemia in subarachnoid hemorrhage based on quantitative EEG: A prospective study in adults.

OBJECTIVES: Delayed cerebral infarction (DCI) has a significant impact on mortality and morbidity of patients with subarachnoid hemorrhage (SAH). The aim of this study was to define quantitative EEG (qEEG) parameters for the early and reliable prediction of DCI and compare the validity and time course of qEEG to standard procedures. METHODS: 12 consecutive unselected SAH patients (8 female, mean age 52 years, Hunt-and-Hess grade I-IV) were prospectively examined. Continuous six channel EEG monitoring was started within 48 h after admission (mean duration 5.2 days; range: 2-12 days). All raw and unselected EEG signal underwent automated artifact rejection, Short Time Fast Fourier Transformation and a detrending procedure in order to analyze regional spectral power changes in different frequency bands. According to clinical standards, transcranial Doppler sonography (TCD) was performed at least on alternate days and repeat cerebral computer tomography (CCT) as needed. RESULTS: 6 patients (50%) developed vasospasm/DCI. Decrease of ⩾40% in power persisting over ⩾5h in the alpha band and ⩾6h in the theta band marked the optimal cut-off to detect DCI (sensitivity 89%, specificity 77% for alpha). EEG changes preceded detection of vasospasm/DCI in standard procedures by 2.3d ays. Changes in the beta and delta band as well as in the alpha/delta ratio demonstrated lower correlation with imminent DCI. CONCLUSIONS: Focal reduction in alpha power may represent a valid, observer independent, non-invasive and continuous marker for vasospasm/DCI in SAH patients. SIGNIFICANCE: qEEG indicates imminent ischemia earlier than established diagnostic tools, such as TCD.

Case report: practicability of functionally based tractography of the optic radiation during presurgical epilepsy work up.

Pre-operative tractography of the optic radiation (OR) has been advised to assess the risk for postoperative visual field deficit (VFD) in certain candidates for resective epilepsy surgery. Diffusion tensor imaging (DTI) tractography relies on a precise anatomical determination of start and target regions of interest (ROIs), such as the lateral geniculate nucleus (LGN) and the primary visual cortex (V1). The post-chiasmal visual pathway and V1 show considerable inter-individual variability, and in epilepsy patients parenchymatous lesions might further complicate this matter. A functionally based tractography (FBT) seems beneficial for precise OR identification. We assessed practicability of FBT for OR identification in a patient with occipital lobe epilepsy due to a temporo-occipital maldevelopmental tumor. The MRI protocol at 3T included a T1-weighted sagittal 3D scan, a T2-weighted axial 2D scan and a DTI scan using an echo planar spin echo sequence. ROIs for fiber tracking of OR (LGN & V1) were determined with T2*-weighted fMRI-based retinotopic assessment. After DTI pre-processing and fiber tracking, paths with similar properties were combined in clusters for visual presentation and OR localization. Retinotopic phase maps allowed for the identification of V1 and LGN for a precise DTI-based reconstruction of OR, which was distant to the patient's tumor. Location and structure of ORs were comparable in each hemisphere. FBT could thus influence the human research of the extrastriate visual pathway and the risk management of post-operative VFD in epilepsy surgery.

Etomidate activates epileptic high frequency oscillations.

OBJECTIVE: The short acting anesthetic etomidate has been shown to provoke epileptic spikes and rarely seizures. Influence of etomidate on the occurrence of epileptic HFO (high frequency oscillations) however is unknown. An HFO inducing effect of etomidate would allow further validation of the substance as a provocation measure in presurgical evaluation as well as provide insights into the common mechanisms of HFO, spike and seizure generation. METHODS: We retrospectively analyzed EEG data from four patients who underwent etomidate activation during invasive video-EEG monitoring with subdural strip electrodes. Spikes were manually selected in raw data, HFO in band pass filtered data (80-250Hz). Rate and spatial distribution of HFO and spikes in three segments were compared: immediately after etomidate administration, as well as during slow wave sleep and while awake. RESULTS: Rates of HFO and spikes increased significantly after etomidate administration: Overall average rates of spikes were 9.7/min during sleep, 10/min while awake and 61.4/min after etomidate. Average HFO rates were 9.5/min during sleep, 8.3/min while awake and 24.4/min after etomidate (p<0.001, non-parametric ANOVA). Spatial distributions of HFO and spikes after administration of etomidate were consistent with the seizure onset zone (SOZ) and area of resection when available (SOZ: two patients; resection: one patient; no information: one patient). Except for spurious events, no additional HFO and spike foci were seen with activation. CONCLUSIONS: Etomidate administration activates spikes and HFO. Spatial distributions do not extend beyond electrodes showing spikes and HFO without Etomidate and seem consistent with the epileptic network. SIGNIFICANCE: Etomidate activation is a safe procedure to provoke not only epileptic spikes but also HFO, which were shown to have a high specificity for the SOZ.

A-trains for intraoperative monitoring in patients with recurrent vestibular schwannoma.

BACKGROUND: Second surgery of recurrent vestibular schwannoma (VS) after previous surgery, stereotactic radiosurgery (SR) or fractionated radiotherapy (FR) carries an increased risk for deterioration of facial nerve function, e.g., due to adhesions, underlining the need for intraoperative monitoring. Facial "Atrain" EMG activity ("traintime") correlates with the degree of postoperative facial palsy. Studies investigating A-trains in VS patients with previous surgery, SR or FR are missing. We therefore investigated the value of A-train monitoring in patients undergoing second surgery for VS. METHOD: Intraoperative EMG data from patients who underwent second surgery for VS after previous surgery, SR and/or FR at our institution between 2006 and 2012 were retrospectively analyzed. Ten patients were selected (5 male): Seven had previous SR/RT and MS, three previous surgery only. Traintime values and distribution was compared to published thresholds and to 77 patients who underwent first surgery for VS during the same time period. RESULTS: A-trains were recorded early after opening of the dura, before facial nerve preparation. Mean traintime was 46.9 s (18.51 s ­ 80.82 s) in patients with previous SR/RT. In patients with previous MS only, traintime was 0.06 s, 0.99 s and 22.46 s. Compared to the literature, traintime was higher than expected in six patients (four with previous SR/RT, two without), respectively seven compared to the 77 patients with first surgery (5 SR/RT). Seven patients with previous SR/RT and none with previous surgery showed diffuse A-train distributions without significant percentages in single channels, compared to 60 of 77 patients with first surgery (p <0.02). CONCLUSIONS: Especially SR/RT, but also previous surgery seems to induce changes in the facial nerve leading to hyperexcitability and exceedingly high traintime values. Based on these findings, A-train monitoring in this specific patient group should be interpreted with caution.

Interictal magnetoencephalography used in magnetic resonance imaging-negative patients with epilepsy.

PURPOSE: This study aims to investigate the contributions of magnetoencephalography (MEG) in magnetic resonance imaging (MRI)-negative patients. METHODS: A total of 18 MRI-negative patients diagnosed with refractory epilepsy, subjected to MEG investigation, and subsequently underwent surgery were selected for retrospective analysis. A 1.5-tesla Magnetom Sonata with an eight-channel head array coil was used. MEG data were obtained using a 74/248-channel system. RESULTS: A total of 16 patients (16/18) had positive MEG results, comprising 12 patients with monofocal localizations, five with multifocal localizations, and one with unremarkable results in MEG. In addition, 12 patients had indicative single photon-emission computed tomography (SPECT), five had indicative fluorodeoxyglucose positron emission tomography (FDG-PET), and all the patients had intracranial electroencephalography (EEG) (14 with subdural electrodes and four with electrocorticography). The intracranial EEG recordings of nine patients were guided by MEG informative results. Among these 18 patients, 10 exhibited good postoperative outcomes (Engel I and II), four of which were completely seizure-free. All these ten patients had clear monofocal localization in MEG, including nine with accordant indicative metabolic changes in either SPECT or FDG-PET, or both. None of the five patients with multifocal localizations achieved good postoperative outcomes. CONCLUSION: For cases with negative MRI findings, epilepsy surgery may be an alternative option for pharmaco-resistant patients if epileptogenic focus localizations by MEG are present in multimodal evaluation.

Multimodality approach in cryptogenic epilepsy with focus on morphometric 3T MRI.

PURPOSE: This study aimed to investigate the potential contribution of morphometric MRI analysis in comparison to other modalities, such as MEG, SPECT and PET, in identifying the epileptogenic focus in patients with cryptogenic epilepsy. PATIENTS AND METHODS: Study inclusion was limited to epilepsy patients with a monolobar focus hypothesis, as concluded from EEG/seizure semiology and the best individual concordance rate. Feature maps, generated by the MATLAB(®) "morphometric analysis program" (MAP), were evaluated by a neuroradiologist blinded to conventional MRI and the focus hypothesis (MAP(1)). In addition, the feature maps were also interpreted by simultaneous matching conventional MRI but, again, with the reader having no knowledge of the focus hypothesis (MAP(2)). RESULTS: In 12 out of 51 patients, true-positive findings were achieved (MAP(1): sensitivity 24%; specificity 96%). The sensitivity of the MAP(1) results was superior extratemporally. After matching conventional MRI, FCD was traced in six of the 12 patients (MAP(2): sensitivity 12%; specificity 100%). MEG sensitivity was 62%. Sensitivity of interictal and ictal SPECT was 20% and 50%, respectively. PET was not as sensitive extratemporally (19%) as temporally (82%). The greatest correspondence with the best individual concordance rate was noted with PET (14/16; 88%) and MEG (8/10; 80%), followed by interictal (5/8; 63%) and ictal (9/15; 60%) SPECT. Results for MAP(1) were 53% (10/19), and 100% for MAP(2) (6/6). CONCLUSION: Although MAP sensitivity and specificity results are lower in comparison to other modalities, implementation of the technique should be considered first, before arranging any further investigations. The present study results offer guidelines for the implementation, interpretation and concordance of diagnostic procedures.

Practice in the perioperative prevention of deep vein thrombosis in german neurosurgical departments: is there a trend towards homogenization?

OBJECTIVE: There was no consensus on the most suitable perioperative prophylaxis of deep vein thrombosis (DVT) in neurosurgical patients. The aim of this work was to review the current practice and search for a standard protocol in the prophylaxis of DVT. METHODS AND MATERIAL: Questionnaires addressing the routine prophylaxis of perioperative DVT for 4 groups of neurosurgical procedures and the estimation of risks and benefits of perioperative heparin (unfractionated and/or low-molecular-weight) administration were sent to 130 neurosurgical departments in Germany. RESULTS: 103 of 130 questionnaires were returned and suitable for analysis. The use of heparin (unfractionated and/or low-molecular-weight) is common, with some variation depending on the type of operation (83.5-99%). In spinal procedures, heparin administration is commonly started early, i. e., between the preoperative and first postoperative day (90.3-97.1%). This differs in intracranial procedures. In most neurosurgical departments heparin administration is stopped at the day of discharge (69.6-77.4% depending on procedure). Enoxaparin is the most commonly used heparin. In spinal as well as in cranial procedures, thrombosis risk reduction is unanimously assumed to be lesser the later administration starts. The estimation of the risks related to heparin injection are considered to be higher in cranial than in spinal operation in the early postoperative period. Most departments use antithrombotic stockings (ATS) irrespective of the type of surgery. However, 11% never use ATS. CONCLUSIONS: In spinal surgery, a trend towards homogenization is observed with the early use of heparin. In intracranial procedures, practice is more heterogenous. The heterogeneity is due to the fact that the data available in the literature does not allow for the identification of an optimal protocol.

Magnetoencephalography adds to the surgical evaluation process.

Summarizing the podium discussion at the AES 2009, strengths and limitations of magnetoencephalography (MEG) are discussed with regard to basic methodological and clinical aspects in routine screening and presurgical evaluation of patients with epilepsies. Current literature and example cases are used to illustrate MEG contribution to clinical decision making, specifically whether a patient with pharmacoresistant epilepsy can move forward to epilepsy surgery. The main conclusion is that the largest role of MEG, as presently performed in the clinical environment, is to increase the number of patients who can go on to surgery, while it should not be used to deny surgery to any patient.

Does electrode placement influence quality of intraoperative monitoring in vestibular schwannoma surgery?

OBJECT: Continuous recording of electromyographic signals (EMG) is a standard method for intraoperative monitoring of facial nerve function in cerebello-pontine angle surgery. Subcutaneous needle electrodes in the facial muscles are used in different setups. The goal of this study was to compare two commonly used electrode setups concering sensitivity for pathological EMG activity. PATIENTS AND METHODS: A group of 10 patients undergoing vestibular schwannoma surgery were examined. Continuous EMG from facial muscles was recorded using needle electrodes in setups according to Kartush or Møller, with narrow or wide interelectrode distances, respectively. Quantity of pathological A-train activity and signal-to-noise ratios were compared between setups. RESULTS: A-train activity was seen in all patients. On average, 37% of A-train activity was seen in the Kartush setup alone, 4% in Møller setups alone and 59% in both setups synchronously (p<0.05; ratio of median train time--Kartush:Møller 3:2). The wide interelectrode distance of the Møller setup was found to be significantly more susceptible to artefacts, especially to low frequency and power line noise. Artefacts were the main reason for the Møller setup to fail detecting A-train activity. CONCLUSIONS: For continuous intraoperative monitoring of facial nerve function, narrow interelectrode distance should be used.

Detection of epileptic spikes by magnetoencephalography and electroencephalography after sleep deprivation.

INTRODUCTION: In diagnosis of epilepsies electrophysiological findings play a key role. While spontaneous electroencephalography (EEG) and EEG with sleep deprivation (EEGsd) are widely evaluated and used, application of magnetoencephalography (MEG) in this field is primarily limited to presurgical assessment of focal epilepsies. METHODS: In this study we retrospectively compared MEG (M/EEG) and EEGsd in 63 (55) patients with focal and generalized epilepsy with regard to occurrence of epileptic spikes. RESULTS: MEG could record epileptic spikes in 38 patients (60%), while EEGsd recorded spikes in only 32 patients (51%). In a group of 55 patients simultaneous MEG/EEG (M/EEG) was able to record spikes in 38 patients (71%) compared to epileptic spikes in 28 patients (51%) recorded by EEGsd. In a subgroup of 17 MR-negative patients simultaneous M/EEG could record epileptic spikes in all patients, while EEGsd was successful in only 11 (64%) of them. CONCLUSION: In this study, MEG showed a tendency to record epileptic spikes in more patients than EEGsd. Furthermore, simultaneous M/EEG has been shown to be especially successful in detection of epileptic spikes in patients with MR-negative epilepsy. This might at least in parts be explained by neocortical predominance of MR-negative epilepsy. Thus, this study motivates prospective studies to evaluate the substitutability of EEGsd by MEG more extensively.

Contrast enhancement and histopathological findings in vestibular schwannoma.

Changes of contrast uptake are considered to indicate the efficacy of therapy in irradiated vestibular schwannomas. We present a case of a large vestibular schwannoma with heterogeneous contrast uptake on MRI. Using neuronavigation, histological samples were obtained during surgery from an area with homogeneous contrast uptake and from a central tumor portion without contrast enhancement on MRI. Intraoperative investigation found no evidence of necrotic tumor, and histopathological examination revealed an active tumor in both sections, with no central necrosis. This finding illustrates the surgical experience that " necrotic tumor areas " on MRI may not be consistent with intraoperative findings. Lack of contrast uptake in previously irradiated schwannomas may not be indicative of effective radiotherapy.

Spikes and epilepsy.

Digital EEG analysis provides significantly more information to the clinical electroencephalographer (EEGer) for scalp as well as for intracranial monitoring than is currently being routinely utilized. When modern data analysis software is used, interictal spikes contain considerably more information than had previously been ascribed to them. To optimize the diagnostic value of the EEG, sleep recordings after sleep deprivation is valuable because focal spikes, unless abundant, are relatively rare in the waking state. Recording time should also be sufficiently long to allow spikes to emerge. Spikes are always pathologic and can be associated with impaired cerebral perfusion, metabolic changes and concomitant behavioral changes. They can also be separated into simple and complex forms which may allow prognostic statements. The simplest way to accomplish this is by placing a cursor on the peak of the spike and see whether or not other channels show latency differences. More precise methods are: comparisons of voltage maps with current source density maps, principal component analysis and distinctions between stationary versus moving dipoles. Averaging of spikes is valuable but care must be taken that only those spikes which have the same distribution are averaged, and when the average is obtained only from the spike peak, propagation may already have occurred. It has been recommended that the midpoint of the ascending negative phase be used as the point for averaging. In intracranial recordings the frequencies above the gamma range should also be assessed. Their small electrical field allows a differentiation between locally generated events from those which are volume conducted and can thereby more accurately reflect the epileptogenic zone(s). High frequency activity can also be recorded from foramen ovale electrodes which enhances their diagnostic utility. It is emphasized that for centers which perform pre-surgical evaluations the software supplied by instrument manufacturers is inadequate and needs to be supplemented by additional commercially available programs. Furthermore, archived data should be used for retrospective investigations and follow-up studies of patients who have undergone either excisions, resections, or multiple subpial transections to evaluate the success rates by taking into account all the properties of interictal and ictal recordings which are mentioned in this article.

[Current clinical-neurophysiological findings in absence epilepsies]. / Aktuelle klinisch-neurophysiologische Befunde bei Absence-Epilepsien.

According to the international classification of epileptic seizures (1981) generalized seizures present ictal signs indicating seizure onset in both hemispheres whereas focal seizures present ictal signs pointing to one hemisphere at seizure onset. Recent neurophysiological studies using MEG, EEG, and fMRI suggest that in case of idiopathic generalized absence epilepsies, activity predominates in specific networks, which include frontoparietal cortical as well as subcortical areas of both hemispheres. In these network regions, epileptic activity can occur circumscribed and focal as spike or spike-wave activity but also widely distributed, bilateral, and homologous. As a consequence to the classification of "generalized" epileptic seizures and syndromes, it might be possible to distinguish a subgroup: regional bilateral homologous epilepsies. These must be distinguished from a pure culture of focal frontal lobe epilepsies, which can also be accompanied by the lead symptom of absences.