Intraoperative brainstem auditory evoked potential pattern and perioperative vasoactive treatment for hearing preservation in vestibular schwannoma surgery.

OBJECTIVE: In vestibular schwannoma surgery, four different intraoperative brainstem auditory evoked potential (BAEP) patterns (stable BAEP, abrupt loss, irreversible progressive loss, reversible loss) can be identified and correlated with postoperative hearing outcome. Patients with reversible loss significantly benefit from postoperative vasoactive treatment consisting of hydroxyethyl starch and nimodipine. The present study investigates the treatment effect in the remaining three BAEP patterns. METHODS: A retrospective analysis was performed in 92 patients operated on for vestibular schwannoma between 1997 and 2005. Between 1997 and 2001, only patients with reversible loss of BAEP received vasoactive medication. Subsequently, all patients operated on between 2001 and 2005 received a 10 day course of therapy, regardless of the BAEP pattern. Serial audiological examinations before, after surgery and after 1 year were performed in all patients. RESULTS: All 30 patients with reversible loss of BAEP received medication, and postoperative hearing preservation was documented in 21 patients. All 13 patients with stable waves showed hearing preservation, regardless of treatment. In all 24 patients with abrupt loss and in all 25 patients with irreversible progressive loss, postoperative anacusis was documented, regardless of treatment. CONCLUSION: In patients with reversible loss of BAEP, a disturbed microcirculation of the cochlear nerve seems to be the underlying pathophysiological factor. In patients with abrupt or irreversible progressive loss, additional mechanical injury of nerve fibres determines hearing outcome. The study provides evidence that for the purpose of hearing preservation, only patients with reversible loss of BAEP benefit from vasoactive treatment.

Specific accumulation of 18F-deoxyglucose in three-dimensional long-term cultures of human and rodent brain tissue.

AIM: Organotypic slice cultures (OSC) of human brain specimens represent an intriguing experimental model for translational studies addressing, e.g., stem cell transplantation in neurodegenerative diseases or targeting invasion by malignant glioma ex vivo. However, long-term viability and phenomena of structural reorganization of human OSC remain to be further characterized. Here, we report the use of (18)F-deoxyglucose (FDG) for evaluating the viability of brain slice preparations obtained either from postnatal rats or human hippocampal specimens. METHODS: Anatomically well preserved human hippocampi obtained from epilepsy surgery and rat hippocampus slice cultures obtained from six day old Wistar rats were dissected into horizontal slices. The slices were incubated with FDG in phosphate buffered saline up to 1 h, either with or without supplementation of glucose at a concentration of 2.5 mg/ml. Radioactivity within the medium or slice cultures was measured using a gamma-counter. In addition, distribution of radioactivity was autoradiographically visualized and quantified as counts per mm(2). RESULTS: In rat hippocampal slices, FDG accumulated with 1 300 000 +/- 68 000 counts/mm(2), whereas the incorporation of the radioactive label in human slices was in the order of 1 500 000 +/- 370 000 counts/mm(2). The elevation of glucose concentration within the medium led to a significant three-fold decrease of FDG accumulation in rat slices and to a 2.4-fold decrease in human specimens. CONCLUSIONS: FDG accumulated in organotypic brain cultures of human or rodent origin. FDG is thus suited to investigate the viability of OSC. Furthermore, these preparations open new ways to study the factors governing cerebral FDG uptake in brain tissue ex vivo.

Prediction of postoperative outcome with special respect to removal of hemosiderin fringe: a study in patients with cavernous haemangiomas associated with symptomatic epilepsy.

PURPOSE: In this study 30 patients with symptomatic epilepsy caused by cavernomas were investigated in a postoperative follow up study to assess predictors for postoperative outcome with respect to indications, time and approach of surgery. METHODS: Thirty patients with cavernomas refractory to medical treatment were scheduled for surgery based on the findings of high-resolution MR imaging and intensive EEG-video monitoring. Postoperative outcome of epilepsy was assessed by follow-up examinations based on the basis of classification by Engel and the International League against epilepsy (ILAE). RESULTS: The following variables were associated with good postoperative outcome: (1) complete resection of hemosiderin fringe surrounding the cavernoma was correlated to less postoperative seizure frequency versus incomplete resection of the hemosiderin fringe according to the outcome protocol of ILAE. (2) Lower duration of epilepsy at the time of operation was correlated to a better postoperative outcome with a benefit for recovery. (3) Absence of hemorrhage before surgery and unifocal seizure onset was a predictor for a favorable outcome, whereas bilateral or multifocal seizure onset zones showed poorer postoperative outcomes. (4) In patients with dual pathology (hippocampal sclerosis in addition to a cavernoma), lesionectomy plus hippocampectomy as opposed to lesionectomy only, had a better outcome than single lesionectomy. CONCLUSION: Postoperative outcome in patients with cavernomas should be the topic of further prospective multicenter studies involving a large number of patients. In addition to the ideal operation time and handling of dual pathology the role of extended resection including perilesional hemorrhages should be taken into account.

Periventricular nodular heterotopia: A challenge for epilepsy surgery.

Pharmacoresistant focal epilepsies due to periventricular nodular heterotopia are a diagnostic and therapeutic challenge because of the need of invasive presurgical diagnostics and the selection of an optimal surgical approach. Invasive investigations in previous studies showed that focal epileptic activity can be correlated predominantly either with one of the nodular heterotopia or with neocortical epileptogenic zones distant to the periventricular nodules. Up to now, invasive recordings were required for localization of epileptic activity and its correlation to heterotopia. The following case presentation reports on a non-invasive approach using magnetic source imaging (MSI) combined with intraoperative ECoG. MSI combines preoperative data from magnetic resonance imaging (MRI) with magnetoencephalography (MEG). The MSI data for definition of the localization of the epileptic activity and functional important areas were coregistered with the intraoperative high-field-MRI and diffusion tensor imaging-based fiber tracking (DTI) of the visual pathway using a neuronavigational system. A neuronavigation-guided surgical resection of the epileptogenic area was performed leaving the heterotopia and the visual tract fibers intact. Postoperatively preservation of the visual fields was documented and the frequency of seizures was markedly reduced.

Deficient memory acquisition in temporal lobe epilepsy is predicted by hippocampal granule cell loss.

BACKGROUND: The hippocampal formation is essentially involved in the formation of conscious memories for facts and events and neurologic diseases affecting the hippocampus associate with severe memory deficits, i.e., temporal lobe epilepsies. METHODS: We studied the degree of declarative memory dysfunction in 24 human subjects with unilateral mesial temporal lobe epilepsy, using the unique possibility to access memory performance of each isolated hippocampus by intracarotid amobarbital anesthesia. Subsequently, hippocampal specimens from the same patients were available for neuropathologic analysis following surgical treatment of intractable seizures. RESULTS: Neuronal cell loss in the dentate gyrus and all hippocampal subfields correlated with memory performance with the exception of CA2. Moreover, multiple regression and partial correlation analyses identified neuronal cell loss within the internal limb of the dentate gyrus, a developmentally distinct subregion of the hippocampal formation known to generate new neurons throughout life, as highly significant predictor for the patient's ability to learn and recall memories. CONCLUSIONS: In accordance with animal studies, the dentate gyrus may play a critical role in the neuronal network associated with memory formation.

Delayed facial nerve paresis following acoustic neuroma resection and postoperative vasoactive treatment.

OBJECT: Delayed facial nerve paresis is a well known clinical phenomenon following acoustic neuroma surgery, typically occurring early during the postoperative course. The clinical course of the delayed facial nerve paresis and intraoperative electromyographic (EMG) signals were evaluated in a subgroup of patients who underwent vasoactive treatment for preservation of hearing and developed secondary deterioration after termination of treatment. METHODS: Between 1990 and 2001 seven patients were identified who received vasoactive treatment for preservation of hearing and developed a delayed facial nerve paresis after termination of medication. Intraoperative facial nerve EMG activity was analyzed in six patients. RESULTS: All patients developed a delayed facial nerve paresis between 2-5 days following termination of a 10 day treatment consisting of HES and nimodipine. Medication was re-initiated and the facial nerve paresis improved in all patients. In two patients intraoperative EMG signals revealed "A-trains" waveform patterns, which are highly suggestive for an immediate postoperative facial nerve paresis, whereas in four patients no pathognomonic EMG patterns could be recorded. CONCLUSIONS: The delayed onset of a facial paresis following termination of vasoactive treatment points to a disturbed microcirculation of the nerve as the main pathophysiological feature. Two groups could be identified on the basis of intraoperative EMG activity. In one group with presence of "A-trains" medication apparently masked the onset of an immediate postoperative facial nerve deficit. Four patients without "A-trains" did not develop a typical delayed facial nerve paresis during vasoactive treatment, but thereafter. The time lag between termination of treatment and onset of a delayed palsy points to a protective effect due to improved microcirculation.

Magnetoencephalography (MEG) predicts focal epileptogenicity in cavernomas.

OBJECTIVE: The aim of this study was to identify the irritative epileptic zone in patients with cavernomas by means of magnetoencephalography (MEG). METHOD: Among 82 patients operated for epilepsy, whose presurgical evaluation had included MEG, histological assessment of the tissue removed had confirmed cavernomas in eight. These eight patients had epilepsy since 18.6 (SD 12.7) years on average. The monitoring lasted about 2.1 (SD 1.3) hours and a median 20.9 (SD 14.3) spikes per hour were recorded. Spontaneous brain activity was recorded by means of a 74 channel dual unit MEG system (Magnes II, 4-D Neuroimaging) with simultaneous EEG recording (31 scalp electrodes). Spike analysis was performed using different source (moving dipole, current density reconstruction) and head models (spherical shells, BEM). Co-registration of neurophysiological and imaging data (MRI) was based upon anatomical landmarks. RESULTS: In 6/8 patients co-localisation from the cavernoma and epileptic zone was found. In two patients the focus was localised in the parieto-occipital lobe, in three patients in the frontal lobe and in three patients in the temporal lobe. In one case of temporal and one case of frontal lobe focus localisation there was no spatial relationship to the cavernoma. CONCLUSION: In cases of focal seizures due to a single cavernoma, MEG may precisely delineate the epileptogenic tissue bordering the lesion. In patients with multiple cavernomas or dual pathology, MSI may reveal the complexity of the case, and contribute to the decision about further invasive diagnostics and more sophisticated therapeutic measures. MEG is a promising method for prediction of the epileptic zone in cavernoma related epilepsies, and thus it can contribute to decision making about and planning of epilepsy surgery.

Epilepsy surgery, resection volume and MSI localization in lesional frontal lobe epilepsy.

To verify whether interictal noninvasive information detected by magnetoencephalography (MEG) recordings can contribute to localize focal epileptic activity relevant for seizure generation in lesional frontal lobe epilepsy, magnetic source imaging (MSI) localizations of epileptic discharges were compared to the extent of neurosurgical resection and postoperative outcome. Preoperative MEG spike localizations were displayed in postoperative magnetic resonance imaging (MRI) scans to check whether dipole sites were located within the resection cavity. Moreover, MEG localizations were compared with results of prolonged video-EEG monitoring and, in three cases, with invasive EEG recordings. Our results in five cases with lesional frontal lobe epilepsy showed that good surgical outcome could be achieved in those patients where the majority of MEG spike localizations were located within the resected brain volume.

Magnetic brain source imaging of focal epileptic activity: a synopsis of 455 cases.

Epilepsy surgery is based upon the minute assessment of brain tissue generating epileptic activity. A number of diagnostic methods are employed in the process of presurgical evaluation, supplying information on various morphological and functional aspects, ultimately integrated into the general result fundamental to the final treatment decision. Magnetic source imaging (MSI), combining structural (MRI) and functional (MEG) data, has been playing an increasingly important role among the tools of presurgical epilepsy evaluation. However, in spite of a considerable number of publications, the samples used have hardly exceeded 50 cases. Therefore, we present a synopsis of 455 epilepsy patients who underwent MSI investigations. Analysis of this substantial data revealed that the average sensitivity of MEG for specific epileptic activity was 70%. Among 131 patients who underwent surgical therapy in addition to antiepileptic drug medication, MSI identified the lobe to be treated in 89%, with results for extratemporal cases being even superior to those with temporal lobe surgery. Introducing a measure to quantify the contribution of MSI to the general result of presurgical evaluation that was applied to 104 patients, the results showed that MSI supplied additional information in 35% and information crucial to final decision making in 10%. Accuracy as well as contribution findings underlined MSI appropriateness even for extratemporal epilepsies, which otherwise frequently prove difficult with respect to focus localization.

The bispectral index declines during neuromuscular block in fully awake persons.

UNLABELLED: Bispectral index (BIS) is an electroencephalographic variable promoted for measuring depth of anesthesia. Electromyographic activity influences surface electroencephalography and the calculation of BIS. In this study, we sought to determine the effect of spontaneous electromyographic activity on BIS. BIS was monitored in three volunteers by using an Aspect A-1000 monitor. The experiment was repeated in one volunteer. Electromyographic activity was recorded. Alcuronium and succinylcholine were administered. No other drugs were used. In parallel with spontaneous electromyographic activity of the facial muscles, BIS decreased in response to muscle relaxation to a minimum value of 33 and, in the repeated measurement, to a minimum value of 9 when total neuromuscular block was achieved. In two volunteers, no total block was achieved. BIS decreased to a minimal value of 64 and 57, respectively. In turn, recovery of BIS coincided with the reappearance of spontaneous electromyographic activity. During the entire experiment, the volunteers had full consciousness. BIS, assessed by software Version 3.31, correlates with spontaneous electromyographic activity of the facial muscles. BIS failed to detect awareness in completely paralyzed subjects. Thus, in paralyzed patients, BIS monitoring may not reliably indicate a decline in sedation and imminent awareness. IMPLICATIONS: The bispectral index (BIS) is an electroencephalographic variable intended for measuring depth of anesthesia. Electromyographic activity influences the calculation of BIS. We found that the administration of a muscle relaxant to unanesthetized volunteers decreases the bispectral index value. Thus, awareness in totally paralyzed patients cannot be excluded.

Localisation of the sensorimotor cortex during surgery for brain tumours: feasibility and waveform patterns of somatosensory evoked potentials.

OBJECTIVE: Intraoperative localisation of the sensorimotor cortex using the phase reversal of somatosensory evoked potentials (SEPs) is an essential tool for surgery in and around the perirolandic gyri, but unsuccessful and perplexing results have been reported. This study examines the effect of tumour masses on the waveform characteristics and feasibility of SEP compared with functional neuronavigation and electrical motor cortex mapping. METHODS: In 230 patients with tumours of the sensorimotor region the SEP phase reversal of N20-P20 was recorded from the exposed cortex using a subdural grid or strip electrode. In one subgroup of 80 patients functional neuronavigation was performed with motor and sensory magnetic source imaging and in one subgroup of 40 patients the motor cortex hand area was localised by electrical stimulation mapping. RESULTS: The intraoperative SEP method was successful in 92% of all patients, it could be shown that the success rate rather depended on the location of the lesion than on preoperative neurological deficits. In 13% of the patients with postcentral tumours no N20-P20 phase reversal was recorded but characteristic polyphasic and high amplitude waves at 25 ms and later made the identification of the postcentral gyrus possible nevertheless. Electrical mapping of the motor cortex took up to 30 minutes until a clear result was obtained. It was successful in 37 patients, but failed in three patients with precentral and central lesions. Functional neuronavigation indicating the tumour margins and the motor and sensory evoked fields was possible in all patients. CONCLUSION: The SEP phase reversal of N20-P20 is a simple and reliable technique, but the success rate is much lower in large central and postcentral tumours. With the use of polyphasic late waveforms the sensorimotor cortex may be localised. By contrast with motor electrical mapping it is less time consuming. Functional neuronavigation is a desirable tool for both preoperative surgical planning and intraoperative use during surgery on perirolandic tumours, but compensation for brain shift, accuracy, and cost effectiveness are still a matter for discussion.

Vasoactive treatment for hearing preservation in acoustic neuroma surgery.

OBJECT: Delayed hearing loss following surgery for acoustic neuroma indicates anatomical and functional preservation of the cochlear nerve and implies that a pathophysiological mechanism is initiated during surgery and continues thereafter. Intraoperative brainstem auditory evoked potentials (BAEPs) typically demonstrate gradual reversible loss of components in these patients. METHODS: Based on this BAEP pattern, a consecutive series of 41 patients with unilateral acoustic neuromas was recruited into a prospective randomized study to investigate hearing outcomes following the natural postoperative course and recuperation after vasoactive medication. Both groups were comparable in patient age, tumor size, and preoperative hearing level. Twenty patients did not receive postoperative medical treatment. In 70% of these patients anacusis was documented and in 30% hearing was preserved. Twenty-one patients were treated with hydroxyethyl starch and nimodipine for an average of 9 days. In 66.6% of these patients hearing was preserved and in 33.3% anacusis occurred. CONCLUSIONS: These results are statistically significant (p < 0.05, chi2 = 5.51) and provide evidence that these surgically treated patients suffer from a disturbed microcirculation that causes delayed hearing loss following removal of acoustic neuromas.

Clinical and neurophysiological observations after superior petrosal vein obstruction during surgery of the cerebellopontine angle: case report.

IMPORTANCE: Preservation of venous drainage during surgery of the cerebellopontine angle has received little attention. CLINICAL PRESENTATION: We describe changes in brainstem auditory evoked potentials after temporary obstruction of the superior petrosal vein during surgical resection of a small meningioma at the petrous apex via a standard suboccipital-lateral approach. Temporary clipping of the petrosal vein resulted in deterioration of the brainstem auditory evoked potentials. The tumor was removed with preservation of the superior petrosal vein. CONCLUSION: A transient postoperative cochlear nerve deficit emphasizes the importance of venous drainage and its preservation during surgery for small lesions of the cerebellopontine angle that do not distort normal anatomic structures.

Contralateral hearing loss as an effect of venous congestion at the ipsilateral inferior colliculus after microvascular decompression: report of a case.

Contralateral hearing loss after surgical procedures within the cerebellopontine angle is rarely seen and its pathophysiological background is not yet understood. A patient with contralateral hearing loss after microvascular decompression for trigeminal neuralgia is described. Ipsilateral brainstem auditory potential (BAEP) monitoring and facial nerve EMG did not show major abnormalities. During otherwise uneventful and successful surgery a branch of the petrosal vein was sacrificed to widen the access to the trigeminal root exit zone. On the third postoperative day the patient complained about contralateral hearing loss, which was verified by audiometry. Contralateral BAEPs showed low amplitudes and delayed interpeak latencies. Brain CT was normal. Brain MRI on the 8th postoperative day disclosed abnormal signals within the ipsilateral inferior colliculus. Intravenous heparinisation was performed and hearing slowly recovered over a 3 month period. Results from this patient offer a pathophysiological mechanism for contralateral hearing loss after cerebellopontine angle surgery, illustrate the importance of venous drainage preservation, gives evidence about the generation of BAEP components within the contralateral brainstem, and stresses the importance of intraoperative BAEP monitoring.

Continuous electromyography monitoring of motor cranial nerves during cerebellopontine angle surgery.

OBJECT: Electromyography (EMG) monitoring is expected to reduce the incidence of motor cranial nerve deficits in cerebellopontine angle surgery. The aim of this study was to provide a detailed analysis of intraoperative EMG phenomena with respect to their surgical significance. METHODS: Using a system that continuously records facial and lower cranial nerve EMG signals during the entire operative procedure, the authors examined 30 patients undergoing surgery on acoustic neuroma (24 patients) or meningioma (six patients). Free-running EMG signals were recorded from muscles targeted by the facial, trigeminal, and lower cranial nerves, and were analyzed off-line with respect to waveform characteristics, frequencies, and amplitudes. Intraoperative measurements were correlated with typical surgical maneuvers and postoperative outcomes. Characteristic EMG discharges were obtained: spikes and bursts were recorded immediately following the direct manipulation of a dissecting instrument near the cranial nerve, but also during periods when the nerve had not yet been exposed. Bursts could be precisely attributed to contact activity. Three distinct types of trains were identified: A, B, and C trains. Whereas B and C trains are irrelevant with respect to postoperative outcome, the A train--a sinusoidal, symmetrical sequence of high-frequency and low-amplitude signals--was observed in 19 patients and could be well correlated with additional postoperative facial nerve paresis (in 18 patients). CONCLUSIONS: It could be demonstrated that the occurrence of A trains is a highly reliable predictor for postoperative facial palsy. Although some degree of functional worsening is to be expected postoperatively, there is a good chance of avoiding major deficits by warning the surgeon early. Continuous EMG monitoring is superior to electrical nerve stimulation or acoustic loudspeaker monitoring alone. The detailed analysis of EMG-waveform characteristics is able to provide more accurate warning criteria during surgery.

["Ghost and mimicry-tumor"--primary CNS lymphoma]. / "Ghost and Mimicry-Tumor"--Primäres ZNS-Lymphom.

In recent years, the frequency of primary cerebral lymphoma (PCNSL) has increased, even among immunocompetent patients. In order to treat the disease optimally, early diagnosis is important. We present three patients with atypical courses of this disease and stress the importance of PCNSL in the differential diagnosis for optimal treatment. In a 75-year-old man, a space-occupying, radiopaque, enhancing CNS lesion disappeared completely after biopsy and short steroid therapy. One year later, the tumor recurred on the other side and again regressed after steroid therapy. The first biopsy showed signs of a papillary tumor, so a choroid plexus papilloma was suspected initially. A 57-year-old woman developed progressive bilateral hearing dysfunction. Lymphocytic pleocytosis led to a primary diagnosis of chronic lymphocytic meningitis. During the further course of disease, the patient developed multiple space-occupying cerebral lesions. Stereotactic biopsy revealed PCNSL. Despite combined chemo- and radiotherapy, a relapse occurred. A 49-year-old woman rapidly developed memory and concentration disturbances. Computed tomography revealed diffuse edema in both hemispheres and MRI detected severe, diffuse, white matter lesions. The CSF revealed lymphocytic pleocytosis including plasma cells. Herpes encephalitis and, after lack of clinical improvement and progression of the MRI changes, acute disseminated encephalomyelitis (ADEM) were suspected. Corticosteroid treatment was initiated. After enormous clinical improvement, a clinical relapse occurred and MRI detected bitemporal and singular space-occupying lesions in the corpus callosum and hypothalamus. Finally, open biopsy showed PCNSL. However, on examination of the treatment history of patient 1, the initial diagnosis must be revised; a PCNSL seems most probable. The phenomenon of tumor remission under steroid administration is rare. In patients 2 and 3, atypical clinical signs and symptoms delayed diagnosis of PCNSL. This tumor can mimic diverse neurological diseases and remit following corticosteroid treatment alone. In unclear cerebral disease, biopsy should be performed early for exact diagnosis and optimal treatment.

Pericollicular approaches to the rhomboid fossa. Part II. Neurophysiological basis.

OBJECT: The authors describe their technique of electrophysiological mapping to assist pericollicular approaches into the rhomboid fossa. METHODS: Surgical approaches to the rhomboid fossa can be optimized by direct electrical stimulation of superficially located nuclei and fibers. Electrophysiological mapping allows identification of facial nerve fibers, nuclei of the abducent and hypoglossal nerves, motor nucleus of the trigeminal nerve, and the ambiguous nucleus. Stimulation at the surface of the rhomboid fossa performed using the threshold technique allows localization above the area that is located closest to the surface. Simultaneous bilateral electromyographic (EMG) recordings from cranial motor nerves obtained during stimulation document the selectivity of evoked EMG responses. With respect to stimulation parameters and based on morphometric measurements, the site of stimulation can be assumed to be the postsynaptic fibers at the axonal cone. Strict limitation to 10 Hz with a maximum stimulation intensity not exceeding 2 mA can be considered safe. Direct side effects of electrical stimulation were not observed. CONCLUSIONS: Electrical stimulation based on morphometric data obtained on superficial brainstem anatomy defines two safe paramedian supra- and infracollicular approaches to the rhomboid fossa and is particularly helpful in treating intrinsic brainstem lesions that displace normal anatomical structures.

The prognostic value of intraoperative BAEP patterns in acoustic neurinoma surgery.

Based on a consecutive series of 70 hearing patients with unilateral acoustic neurinomas and intraoperative monitoring of brain-stem auditory evoked potentials (BAEP), 4 dynamic BAEP patterns could be characterized. These patterns correspond with early and late postoperative hearing outcome. All patients with stable wave V (pattern 1) showed definite hearing preservation, all patients with irreversible abrupt loss of BAEP (pattern 2) lost their hearing, despite early hearing preservation in two cases. All patients with irreversible progressive loss of either wave I or wave V (pattern 3) eventually suffered from definite postoperative hearing loss, despite early hearing preservation in two cases. Those cases with intraoperative reversible loss of BAEP (pattern 4) showed variable short and long term hearing outcome. In 34% hearing was preserved, 44% suffered from postoperative hearing loss, the remaining 22% showed postoperative hearing fluctuation, either as a delayed hearing loss or as reversible hearing loss. Postoperative hearing fluctuation indicates anatomical and functional preservation of the cochlear nerve during surgery and is suggestive of a pathophysiological mechanism initiated during the surgical procedure and continuing thereafter. Patients at risk for delayed hearing loss can be identified during surgery by a characteristic BAEP pattern and may benefit from vasoactive treatment.

Functional neuronavigation with magnetoencephalography: outcome in 50 patients with lesions around the motor cortex.

OBJECT: The authors conducted a study to evaluate the clinical outcome in 50 patients with lesions around the motor cortex who underwent surgery in which functional neuronavigation was performed. METHODS: The sensorimotor cortex was identified in all patients with the use of magnetoencephalography (MEG). The MEG-source localizations were superimposed onto a three-dimensional magnetic resonance image and the image data set was implemented into a neuronavigation system. Based on this setup, the surgeon chose the best surgical strategy. During surgery, the pre- and postcentral gyri were identified by neuronavigation and, in addition, the central sulcus was localized using intraoperative recording of somatosensory evoked potentials. In all cases MEG localizations of the sensory or motor cortex were correct. In 30% of the patients preoperative paresis improved, in 66% no additional deficits occurred, and in only 4% (two patients) deterioration of neurological function occurred. In one of these patients the deterioration was not related to the procedure. CONCLUSIONS: The method of incorporating functional data into neuronavigation systems is a promising tool that can be used in more radical surgery to lessen morbidity around eloquent brain areas.