Johannes Sarnthein

Over the last two decades a favourable course for treated or nontreated brainstem cavernomas has become possible with enhanced diagnostic tools and clinical experience, as well as minimally invasive microsurgical improvements. Currently, brainstem cavernoma can be treated microsurgically with excellent results and an acceptable morbidity rate. The preferred surgical route has progressively shifted from a dorsal to a lateral approach, but this remains dependent on the location of the lesion in the brainstem. Surgical evaluation and management of all cases of this rare disease should be performed by experienced teams from the outset.

During surgeries that put the visual pathway at risk of injury, continuous monitoring of the visual function is desirable. However, the intraoperative monitoring of the visual evoked potential (VEP) is not yet widely used. We evaluate here the clinical utility of intraoperative VEP monitoring. We analyzed retrospectively 46 consecutive surgeries in 2011-2013. High luminance stimulating devices delivered flash stimuli on the closed eyelid during intravenous anesthesia. We monitored VEP features N75 and P100 and took patients' preoperative and postoperative visual function from patient charts. Postoperative ophthalmologic workup was performed in 25 (54%) patients and preoperatively in 28 (61%) patients. VEP recordings were feasible in 62 of 85 eyes (73%) in 46 patients. All 23 eyes without VEP had impaired vision. During surgery, VEPs remained stable throughout surgery in 50 eyes. In 44 of these, visual function did not deteriorate and three patients (6 eyes) developed hemianopia....

ABSTRACT Neurophysiological studies at the cellular level (microelectrode unit activity recordings and local field potentials) as well as electro- and magnetoencephalographic recordings provide converging evidence for a thalamocortical dysregulation at the source of chronic neurogenic pain of both peripheral and central origin. These indicate an increase of low frequency thalamocortical rhythmicity originating in disfacilitation of thalamic relay neurons, followed by cortical activation due to asymmetries of corticocortical inhibition. This process, called thalamocortical dysrhythmia, might become self-sustained and, thus, chronic due to recurrent thalamoreticulothalamic and corticoreticulothalamic feedback inhibition. Our surgical approach is centered on re-establishment of normal thalamocortical oscillatory activity using small, strategically placed medial thalamic and prethalamic lesions. These reduce the increased low frequency thalamocortical recurrent network activity via low frequency desamplification and thalamic disinhibition, providing long term therapeutic efficiency coupled with sparing of the specific thalamocortical loops.

BACKGROUND AND STUDY OBJECT: A leak-proof dura closure after elective surgery for intradural spinal lesions is important to achieve an uncomplicated postoperative course. Because many different closure techniques and dura substitutes exist, we tried to identify the superior material and technique to avoid cerebrospinal fluid leaks (CSFLs). Between 2004 and 2009, 91 patients underwent surgical treatment of intradural spinal pathologies with primary dura closure with or without the use of dura substitutes at our institution. Pre- and postoperative images and the clinical course were analyzed retrospectively with respect to the occurrence of CSFL. In 34% of the 91 patients, radiological signs of CSFL were observed. A total of 12 patients (13%) were symptomatic for CSFL and required a single puncture, lumbar drain, or surgical revision. No significant relation between CSFL and patient characteristics, underlying diagnosis, localization, or extension was noted. In contrast, the incidence of CSFL was significantly increased if more than one substitute for dura closure was used. The results showed that 41.7% of these patients showed radiological signs of CSFL as compared with 10.4% of patients in which only a single material was used. In our study, none of the applied products appeared to be superior to the others. Surgery with the combined use of multiple dura closure substitutes was associated with the enhanced incidence of postoperative CSFL. However, our findings concerning the various dura sealants could not be used to compare those different materials, due to the great variety of combinations of dura sealants and the retrospective analysis of the data.

Sleep changes are frequent in stroke patients and predict a poor outcome. It remains unclear how sleep influences stroke evolution and recovery. We assessed effects of sleep disruption on brain damage and on the expression of axon sprouting genes after focal cerebral ischemia in rats. 12 h after ischemia induced by occlusion of the middle cerebral artery, rats were subjected to sleep disruption including sleep deprivation for 12h (SDpv12h) and sleep disturbances (SDis) by SDpv12h for consecutive 3 days. Control groups included ischemia without SDpv12h or SDis, sham surgery plus SDis and sham surgery without SDis. Sleep changes were evaluated based on EEG and EMG recordings. SDpv12h increased the infarct volume by 40% (SDpv12h 82.8 +/- 10.9 vs. control 59.2 +/- 13.9 mm3, P = 0.008) and SDis by 76% (SDis 58.8 +/- 20.4 vs. control 33.8 +/- 6.3 mm3, P = 0.017). SDpv12h also increased the number of damaged cells, visualized by TUNEL staining, by 137% (SDpv12h 46.8 +/- 15 vs. control 19.7...

Intraoperative Neurophysiological Mo-nitoring (IONM) identifies eloquent areas or nerves fibers during neurosurgical interventions and monitors their function. For several interventions IONM has become mandatory in neurosurgery. IONM increases patient safety during surgery as the risk of neurological deficits is reduced. Safer surgery reduces the time needed for the intervention and thereby reduces risk. IONM contributes to complete resection of tumors, which in turn prolongs patients' survival. Complicated surgical interventions associated with an elevated risk of neurological deficits have only become possible due to IONM. IONM comprises a variety of procedures that are selected for a particular intervention. With appropriate selection of the procedures IONM has been shown to improve neurological and functional outcome after neurosurgical interventions.

We investigate defects and diffusion in solid Li3N, a superionic conductor, using the projector-augmented-wave implementation of Car-Parrinello molecular dynamics. Static calculations are used to discuss the structure and formation of Li vacancies, where we also consider hydrogen interstitials. The barrier for lithium jumps to vacant adjacent sites in the Li2N plane (⊥c) was found to be extremely small, namely, 0.004

We measured coherence between the electro- encephalogram at different scalp sites while human subjects performed delayed response tasks. The tasks required the retention of either verbalizable strings of characters or ab- stract line drawings. In both types of tasks, a significant enhancement in coherence in the u range (4-7 Hz) was found between prefrontal and posterior electrodes during 4-s reten- tion intervals. During 6-s perception intervals, far fewer increases in u coherence were found. Also in other frequency bands, coherence increased; however, the patterns of enhance- ment made a relevance for working memory processes seem unlikely. Our results suggest that working memory involves synchronization between prefrontal and posterior association cortex by phase-locked, low frequency (4-7 Hz) brain activity.

Cortical activity and perception are not driven by the external stimulus alone; rather sensory information has to be integrated with various other internal constraints such as expectations, recent memories, planned actions, etc. The question is how large scale integration over many remote and size-varying processes might be performed by the brain. We have conducted a series of EEG recordings during processes thought to involve neuronal assemblies of varying complexity. While local synchronization during visual processing evolved in the gamma frequency range, synchronization between neighboring temporal and parietal cortex during multimodal semantic processing evolved in a lower, the beta1 (12-18 Hz) frequency range, and long range fronto-parietal interactions during working memory retention and mental imagery evolved in the theta and alpha (4-8 Hz, 8-12 Hz) frequency range. Thus, a relationship seems to exist between the extent of functional integration and the synchronization-frequency. In particular, long-range interactions in the alpha and theta ranges seem specifically involved in processing of internal mental context, i.e. for top-down processing. We propose that large scale integration is performed by synchronization among neurons and neuronal assemblies evolving in different frequency ranges.

Research investigating the pathophysiology of Parkinson's disease (PD) mostly focuses on basal ganglia dysfunction. However, the main output from the basal ganglia is via the thalamus, and corticothalamic feedback constitutes the primary source of synapses in the thalamus. We therefore focus on the thalamocortical interplay. During the surgical intervention in six patients, local field potentials (LFPs) were recorded from pallidal-recipient thalamic nuclei VA and VLa. Simultaneously, EEG was recorded from several sites on the scalp. The highest thalamocortical coherence was found in the theta frequency band (4-9 Hz) with a mean peak frequency of 7.5 Hz. The magnitude of thalamocortical theta coherence was comparable to the magnitude of EEG coherence between scalp electrode pairs. Thalamocortical theta coherence reached 70% and was maximal with frontal scalp sites on both hemispheres. In the 13-20 Hz beta frequency band, maximal coherence was comparatively low but localized on the scalp ipsilateral to the site of thalamic LFP recording. The high thalamocortical coherence underlines the importance of thalamic function for the genesis of scalp EEG. We discuss the PD pathophysiology within the framework of dysrhythmic thalamocortical interplay, which has important consequences for the choice of therapeutic strategy in patients with severe forms of PD.

The spatial complexity of highly vulnerable structures makes surgical resection of brainstem cavernomas (BSC) a challenging procedure. Diffusion tensor imaging (DTI) allows for the visualization of white matter tracts and enables a better understanding of the anatomical location of corticospinal and sensory tracts before and after surgery.We investigated the feasibility and clinical usefulness of DTI-based fiber tractography in patients with BSC.Pre- and postoperative DTI visualization of corticospinal and sensory tracts were retrospectively analyzed in 23 individuals with BSC. Preoperative and postoperative DTI-fiber accuracy were associated to the neurological findings. Preoperatively, the corticospinal tracts were visualized in 90 % of the cases and the sensory tracts were visualized in 74 % of the cases. Postoperatively, the corticospinal tracts were visualized in 97 % of the cases and the sensory tracts could be visualized in 80 % of the cases. In all cases, the BSC had caused displacement, thinning, or interruption of the fiber tracts to various degrees. Tract visualization was associated with pre- and postoperative neurological findings. Postoperative damage of the corticospinal tracts was observed in two patients. On follow-up, the Patzold Rating (PR) improved in 19 out of 23 patients (83 %, p = 0.0002).This study confirms that DTI tractography allows accurate and detailed white matter tract visualization in the brainstem, even when an intraaxial lesion affects this structure. Furthermore, visualizing the tracts adjacent to the lesion adds to our understanding of the distorted intrinsic brainstem anatomy and it may assists in planning the surgical approach in specific cases.

During surgeries that put the facial nerve at risk for injury, its function can be continuously monitored by transcranial facial nerve motor evoked potentials (FNMEPs) in facial nerve target muscles. Despite their advantages, FNMEPs are not yet widely used. While most authors use a 50% reduction in FNMEP response amplitudes as a warning criterion, in this paper the authors' approach was to keep the response amplitude constant by increasing the stimulation intensity and to establish a warning criterion based on the "threshold-level" method. The authors included 34 consecutive procedures involving 33 adult patients (median age 47 years) in whom FNMEPs were monitored. A threshold increase greater than 20 mA for eliciting FNMEPs in the most reliable facial nerve target muscle was considered a prediction of reduced postoperative facial nerve function, and subsequently a warning was issued to the surgeon. Preoperative and early postoperative function was documented using the House-Brackmann grading system. Monitoring of FNMEPs was feasible in all 34 surgeries in at least one facial nerve target muscle. The mentalis muscle yielded the best results. The House-Brackmann grade deteriorated in 17 (50%) of 34 cases. The warning criterion was reached in 18 (53%) of 34 cases, which predicted an 83% risk of House-Brackmann grade deterioration. Sensitivity amounted to 88% (CI 64%-99%) and specificity to 82% (CI 57%-96%). Deterioration of FNMEPs and a worse House-Brackmann grade showed a high degree of association (p < 0.001). The impact of FNMEP monitoring on surgical strategy is exemplified in an illustrative case. In surgeries that put the facial nerve at risk, the intraoperative increase in FNMEP stimulation threshold was closely correlated to postoperative facial nerve dysfunction. Monitoring of FNMEPs is a valid indicator of facial nerve function in skull base surgery. It should be used as an adjunct to direct electrical facial nerve stimulation and continuous electromyographic monitoring of facial nerve target muscles.

Symptomatic patients with a brainstem cavernoma are treated surgically with increasing frequency. Generally, the patient's benefit from this difficult surgical intervention is quantified by the assessment of neurological symptoms. To document the beneficial effect of surgery in a larger patient population by assessing the postoperative quality of life (QoL). In a series of 71 surgically treated patients, a detailed neurological status was assessed by Patzold Rating and Karnofsky Performance Status Scale. Patients rated their QoL with the Short Form 36 Health Survey. To document the effect of surgery on QoL, we devised a supplementary questionnaire. The last 24 patients completed Short Form 36 Health Survey pre- and postoperatively. Karnofsky Performance Status Scale improved in 44 of 71 surgical patients (62%), remained unchanged in 19 (27%), and deteriorated in 8 (11%) individuals. Patzold Rating showed a more detailed picture of the neurological symptoms. It correlated significantly with Karnofsky Performance Status Scale, which underscores its usefulness for patients with brainstem lesions. In the Short Form 36 Health Survey score, the Mental Component Summary improved with surgery (paired test, P = .015). In addition, 58 individuals (82%) declared a clear subjective benefit of surgery. The results of this large series support the notion that microsurgical removal of a brainstem cavernoma represents an effective therapy in experienced hands and is generally associated with good clinical outcome, both neurologically and in terms of QoL.

Surgical exposure of intrinsic brainstem lesions through the floor of the 4th ventricle requires precise identification of facial nerve (CN VII) fibers to avoid damage. To assess the shape, size, and variability of the area where the facial nerve can be stimulated electrophysiologically on the surface of the rhomboid fossa. Over a period of 18 months, 20 patients were operated on for various brainstem and/or cerebellar lesions. Facial nerve fibers were stimulated to yield compound muscle action potentials (CMAP) in the target muscles. Using the sites of CMAP yield, a detailed functional map of the rhomboid fossa was constructed for each patient. Lesions resected included 14 gliomas, 5 cavernomas, and 1 epidermoid cyst. Of 40 response areas mapped, 19 reached the median sulcus. The distance from the obex to the caudal border of the response area ranged from 8 to 27 mm (median, 17 mm). The rostrocaudal length of the response area ranged from 2 to 15 mm (median, 5 mm). Facial nerve response areas showed large variability in size and position, even in patients with significant distance between the facial colliculus and underlying pathological lesion. Lesions located close to the facial colliculus markedly distorted the response area. This is the first documentation of variability in the CN VII response area in the rhomboid fossa. Knowledge of this remarkable variability may facilitate the assessment of safe entry zones to the brainstem and may contribute to improved outcome following neurosurgical interventions within this sensitive area of the brain.

Acquired skull deformities are common and most likely treated surgically by cranioplasty. Since data on patient aesthetic outcome after cranioplasty are rare in literature, we aimed to assess patient satisfaction after polymethyl-methacrylate (PMMA) cranioplasty in this study using a questionnaire. A patient questionnaire was developed to evaluate the grade of satisfaction after surgery. After approval by the institutional ethical review board, we were allowed to send to all 115 patients, who received a cranioplasty from 2001 to 2008 at the University Hospital of Zurich, our questionnaire once to retrospectively analyze the patient response together with the patient hospital records. Out of 115 patients, 36 patients were lost to follow-up and our questionnaire was sent out once to 79 patients. Sixty-three of 79 patients replied to the questionnaire (79·7%) and 16 did not reply. Seventeen declined to participate in this study and out of the remaining 46 patients (58·2%, 18 women, mean age 54 years, range 20-83 years), who agreed to participate in this study, 22 (47·8%) judged their cranioplasty to be aesthetically 'excellent', 16 (34·8%) 'favorable' and 4 (8·7%) 'poor'. Another four patients (8·7%) were not satisfied, asking for a surgical revision. Patient age and gender was not related to the assessment of the aesthetic result. A higher satisfaction grade was found in patients with primary PMMA cranioplasty compared to PMMA cranioplasty implanted during a second surgery (Fisher's exact test, P = 0·031). A dent was strongly associated with absence of satisfaction (P<0·01, Fisher's exact test). Our questionnaire was suitable to assess patient satisfaction after cranioplasty. Localization of cranioplasty showed to be an important factor of aesthetic outcome, especially in the fronto-temporal region where a carefully planned reconstruction should be performed to guarantee an excellent grade of satisfaction after surgery.

Cortical activity and perception are not driven by the external stimulus alone; rather sensory information has to be integrated with various other internal constraints such as expectations, recent memories, planned actions, etc. The question is how large scale integration over many remote and size-varying processes might be performed by the brain. We have conducted a series of EEG recordings during processes thought to involve neuronal assemblies of varying complexity. While local synchronization during visual processing evolved in the gamma frequency range, synchronization between neighboring temporal and parietal cortex during multimodal semantic processing evolved in a lower, the beta1 (12-18 Hz) frequency range, and long range fronto-parietal interactions during working memory retention and mental imagery evolved in the theta and alpha (4-8 Hz, 8-12 Hz) frequency range. Thus, a relationship seems to exist between the extent of functional integration and the synchronization-frequency. In particular, long-range interactions in the alpha and theta ranges seem specifically involved in processing of internal mental context, i.e. for top-down processing. We propose that large scale integration is performed by synchronization among neurons and neuronal assemblies evolving in different frequency ranges.

During neurosurgical intracranial vascular manipulations, surgeons need early feed-back on the effects of temporary vascular occlusion. In surgical practice, commonly the amplitude of somatosensory evoked potentials (SSEP) is monitored. However, the latency between an ischemic event and the drop of SSEP amplitude may amount to several minutes. Therefore intracranial electroencephalogram (iEEG) is tested for its predictive value. During surgery in 13 patients, SSEP was recorded simultaneously with iEEG. iEEG was analyzed real-time in the frequency domain. Spectral observables of the iEEG were validated on the basis of SSEP by computing the statistical correlation first for the whole data set, then for salient events occurring in the SSEP in the group of patients, and finally for salient events occurring in single patients. Placement of subdural strip electrodes was compatible with standard surgical routine. Maximal correlation between time series of iEEG and SSEP was found for relative alpha power, which preceded the drop of SSEP by 7min. iEEG is feasible during neurosurgical intracranial vascular manipulations. Monitoring relative alpha power detects salient events earlier than SSEP. Early detection of salient events facilitates early reaction of the surgeon and may thereby aid to further reduce intraoperative morbidity.

ABSTRACT We have performed a set of experiments that correlate EEG spectral parameters with cognitive functions. The tasks (visual perception, supramodal object recognition, short-term memory) were chosen so that the cortical area involved extended over different length scales. The extent of the cognitive neuronal assemblies correlated inversely with the frequency where EEG synchronization was found. This provides a further relation between experiment and the theory put forward in the Nunez target article.