[Identification of highly specific electroencephalographic patterns in patients with neuroepithelial tumors of the III ventricle by algorithmic methods].

An algorithm was suggested for identifying highly specific electroencephalographic (EEG) patterns in neurooncologic patients. The algorithm provides selection of patients with their further classification into main and control groups based on the already existing database of EEG indicators; requests to it; generation of mono-indicator candidates for EEG-patterns on the basis of a 4-dipole table for selecting and verifying sensitive and specific EEG patterns and outlining the best ones. Our material included 368 patients with basal-diencephalic tumors. Algorithmic methods revealed new EEG patterns in patients with different anatomical and topographical variants of neuroepithelial tumors in the III ventricle. We think it reasonable to use the revealed syndromes to improve diagnosis and identify pathophysiological basis of clinical syndromes.

[Compression cervical spine cord injury in patients with posterior cranial fossa tumors operated on in the sitting position: two cases with different outcomes].

The paper describes two cases of posterior cranial fossa pathology, operated on in the sitting position on the operating table. In one case, symptoms of cervical spine injury caused by undiagnosed preoperative cervical spine pathology emerged in a female patient in the early postoperative period. In the other case, cervical spine pathology was diagnosed before surgery and evoked potentials were monitored to prevent possible cervical spine injury in the sitting position during an operation.

[Planning of surgical approach to intracerebral tumors of the hemispheres using fMRI, neuronavigation, and electrophysiological monitoring].

The paper discusses pre- and intraoperative application of different guiding techniques (frameless neuronavigation, fMRI, electrophysiological monitoring). We performed comparative analysis of different combinations of these methods. 74 patients with intracerebral tumors involving eloquent areas (sensorimotor cortex in 56 and speech zones in 18) were operated. In 9 cases 'awake surgery' was applied. We found that frameless navigation combined with brain mapping allows to optimize planning of surgical approach and to decrease postoperative neurological deficit. Also in certain cases 'awake craniotomy' can be replaced by fMRI and neuronavigation.

[Intraoperative identification of oculomotor, trochlear and abducent nerves in surgery of invasive cranioorbital tumors (new technique)].

BACKGROUND: Aim of the study was to evaluate effectiveness of intraoperative identification of oculomotor nerves (OMN) in resection of skull base tumors invading superior orbital fissure and cavernous sinus. MATERIALS AND METHODS: 69 patients with cranioorbital tumors operated in Burdenko Neurosurgical Institute (Moscow, Russia) since 2000 until 2005 were included in the study. They were divided into 2 groups: 19 patients treated with intraoperative identification of OMN and 50 patients in the control group. Craniorbital meningiomas were in the majority among all cases. Intraoperative identification of OMN was performed using coaxial electrode while muscular response was registered through electrodes inserted in m. levator palpebrae superioris, m. obliquus superior and m. rectus lateralis (for III, IV and VI cranial nerves, respectively). Identification of IMN trunci was repeated throughout the whole stage of tumor resection for their preservation. RESULTS: comparison of dynamics of oculomotor dysfunction in early postoperative period in patients of both groups demonstrated that intraoperative identification of OMN allowed to decrease the frequency of oculomotor deficit. The rates in main and control groups were: for III and IV nerves--37% and 68% (p < 0.05), for VI nerve--47% and 54% (p > 0.05), respectively. CONCLUSION: application of intraoperative identification of OMN allows to decrease the risk of oculomotor deterioration due to III and IV nerve dysfunction by 1.8 times. Technically the method is quite simple and not time-consuming procedure.

[Identification of the cochlear nerve in surgical removal of vestibular schwannomas].

Review of methods which allow intraoperative identifying and monitoring of cochlear and facial nerves in resection of vestibular schwannomas is presented. We describe a case of successful identification and functional preservation of facial and cochlear nerves in a patient with acoustic neuroma. Detailed description of neurophysiological and neurosurgical aspects of surgical technique intended to preserve auditory functions is given. According to some authors, application of intraoperative neurophysiological techniques in surgery of vestibular schwannomas allows to preserve not only anatomical but also functional integrity of neural structures as well.

[The identification and functional tracking of the facial nerve during the removal of tumors of the cerebellopontine angle]. / Identifikatsiia i slezhenie za sostoianiem litsevogo nerva vo vremia udaleniia opukholei mostomozzhechkovogo ugla.

Intracranial identification by electrostimulation and monitoring of the status of the facial nerve was intraoperatively used in 21 patients with cerebellopontine angle tumors of varying histological structure. Monopolar and bipolar electrostimulation, as well as electromyography and mechanography for recording the function of the facial nerve were compared. During removal of cerebellopontine angle tumors, identification and monitoring of the function of the facial nerve provide anatomic retention of this nerve when the tumor is radically eliminated. This is of essential significance for acoustic neurinomas. A combination of monopolar and bipolar stimulation for identification of the facial nerve simplifies removal of these tumors. As compared with electromyography, mechanography of facial nerve function during these operations is a more convenient technique due to the simplicity and absence of false operation for electric interferences. The study provided the optimum procedure for intracranial stimulation to identify the facial nerve within the cerebellopontine angle.

[Somatosensory evoked potentials in the assessment of cerebral ischemia in combined operations for intracranial aneurysms]. / Somatosensornye vyzvannye potentsialy v otsenke ishemii golovnogo mozga pri kombinirovannykh operatsiiakh vnutricherepnykh anevrizm.

Combined surgery of extra-intracranial anastomosis (EICA) and occlusion of the afferent vessel by means of a balloon catheter was made in 14 patients with giant aneurysms of the internal carotid (IC) and middle meningeal artery (MMA). MMA was excluded without previously creating EICA in another patient. The purpose of the study was to define the informative value of a somatosensory evoked potential (SSEP) as an intraoperative criteria for possible permanent occlusion of the major vessel. In 9 patients, IC or MMA occlusion was shown to cause neither intraoperative SSEP changes no postoperative neurological defect. After IC occlusion one case showed 25% reductions in the SSEP amplitude, which was not followed by neurological deterioration. In another patient with IC occlusion, 40% decreases in the cortical response amplitude resulted in moderate postoperative hemiparesis. In one patient with transient IC occlusion, 50% falls in the SSEP amplitude were accompanied by poor EICA function, which made permanent IC occlusion be avoided. However, postoperative neurological defect progression was detected in 3 patients without intraoperative SSEP changes. The findings suggest that SSEP may be used to determine whether IC and MMA can be excluded at surgery for aneurysms. However, no intraoperative SSEP changes does not predict the constancy of a patient's neurological status.

[Intraoprative identification and monitoring of motor structures of the brain stem]. / Intraoperatsionnaia identifikatsiia i monitoring sostoianiia dvigatel'nykh struktur stvola mozga.

The purpose of this work was to evaluate the method of identification of motor structures of the bottom of the IV ventricle in order to find the zone through which it is possible to safely approach the bulky formation and to assess the efficacy of subsequent monitoring of these structures for the prevention of their intraoperative injury. Fourteen patients with bulky tumors of the caudal portions of the brain stem aged 4 to 57 were examined. Motor structures of the brain stem (nerves VII or IX, X, and XII, depending on the site of injury) were identified by direct electrostimulation of the surface of the rhomboid fossa and recording of the motor functions by mechanography of EMG. The results indicate that intraoperative identification of motor structures followed by monitoring thereof is a useful instrument which helps reduce the surgical risk of injuring these structures during surgery on the brain stem.

[Monitoring of eye movements in surgery of the brain stem and parastem structures]. / Monitoring dvizhenii glaz pri khirurgicheskikh vmeshatel'stvakh na stvole mozga i parastvolovykh strukturakh.

Intraoperative electrooculograms (EOG) of 44 patients with bulky formations in the posterior cranial fossa demonstrated a good correlation of the sum of EOG waves caused by mechanical stimulation (aspiration, retraction, etc.) and the sum of complexes of EOG waves, on one hand, and the outcome, on other, in patients with brain stem involvement and less so in those with involvement of the cerebellum. The method is not informative for predicting the status of stem structures in surgery on the pontocerebellar angle. Stimulation of cerebral tissue caused by electrocoagulation cannot be recognized by EOG because it is associated with electric artefacts.

[Monitoring of short latent evoked potentials during brain stem surgery]. / Monitoring korotkolatentnykh vyzvannykh potentsialov vo vremia operatsii na stvole golovnogo mozga.

The studies were carried out in 33 patients with intrastem volumetric tumors. In 6 patients the monitoring was impossible because of technological problems. Somatosensory evoked potentials (SSEP) were recorded in 10 and acoustic stem evoked potentials (ASEP) in 18 out of 27 patients and the findings correlated to changes in the neurological status on day 1 postoperation. In 3 out of 9 patients operated on in a sitting posture SSEP monitoring during the main stage of the operation became impossible because the response disappeared due to an air layer above the parietal cortex. Transitory or constant changes in SSEP at the stage of tumor removal were detected in 5 patients. In 9 patients intraoperative changes in ASEP were recorded. False-positive results of ASEP monitoring were obtained in 4 cases. In 2 cases a discrepancy between intraoperative changes of SSEP and the postoperative neurologic deficit were detected. The authors discuss the technological and methodological problems of intraoperative monitoring of evoked potentials and approaches to solution of these problems.

[Monitoring somatosensory evoked potentials during surgery of cerebral vessels]. / Monitoring somatosensornykh vyzvannykh potentsialov vo vremia operatsii na sosudakh golovnogo mozga.

In 43 patients serial SSER recordings were made during operations for the clipping of arterial aneurysms of cerebral vessels performed under controlled arterial hypotension. SSER recordings during the preliminary phase of the operation showed an average decrease in the response amplitude of 20% during trepanation and a reduction (by 23% of the initial value) during the phase of arterial hypotension. The response recovered to 84% of its initial level by the moment of the beginning of the operation. There was no statistically significant relationship between serial SSER parameter values during arterial pressure reduction and the duration or degree of hypotension. The results testify to the higher information content of such SSER parameters as the amplitude of the first positive complex, as compared with latency criteria and in particular the CCT. It has also been found that a significant increase in the information value of the SSER for the evaluation of ischemia effect on the brain function may be obtained by synchronous stimulation of both arms and registration of cortical responses from both hemispheres.

[Changes in evoked potentials to light in the presence of lesions of the diencephalic and brainstem regions of the human brain]. / Izmenenie vyzvannykh potentsialov na svet pri porazhenii diéntsefal'nykh i stvolovykh otdelov mozga u cheloveka.

Evoked potentials (EPs) to light were studied in groups of patients with tumours of basal-diencephalic localization (24 patients) and at the brain-stem level (24 patients), in comparison with 11 normal subjects. In the first group, a decrease of amplitude and increase of response duration were found in the frontal cortical areas, with simultaneous reduction of intrahemispheric differences due to decrease of low-frequency components in the EP spectra by amplitude in fronto-central parts, and of alpha- and beta-frequencies in the occipital parts of the hemispheres. EP changes resulting from brain-stem tumors were more expressed than in the case of cerebellar tumors. In patients with foci causing a pronounced irritation of the brain-stem, a decrease in responses amplitude was observed accompanied by an amplitude lowering of delta- and theta-frequencies in EPs-spectra in the frontal, central and temporal leads, with no changes in the occipital leads. The obtained data testify to functional inequivalence and independence of different EP frequency components suggesting that the methods of studying the EP frequency structure are informative and efficient.