RESUMEN
OBJECTIVE: To assess whether intraoperative subcortical mapping of the visual pathways during brain surgeries was feasible. METHODS: Subcortico-cortical evoked potentials (SCEPs: 30 stimulations/site, biphasic single pulse, 1.3 Hz, 0.2 ms/phase, maximum 10 mA; bipolar probe) were measured in 12 patients for stimulation of the optic radiation, Meyer's loop or optic nerve. Recorded sites were bilateral central, parietal, parieto-occipital, occipital (subdermal scalp electrodes, 5-4000 Hz). The minimum distances from the stimulation locations, i.e. the closest border of the resection cavity to the diffusion tensor imaging based visual pathways, were evaluated postoperatively (smallest distance across coronal, sagittal and axial planes). RESULTS: Stimulation elicited SCEPs when the visual tracts were close (≤4.5 mm). The responses consisted of a short (P1, 3.0-5.6 ms; 8/8 patients) and of a middle (P2, 15-21.6 ms; 3/8 patients) latency waveforms. In agreement with the neuroanatomy, ipsilateral occipital responses were obtained for temporal or parietal stimulations, and bi-occipital responses for optic nerve stimulations. CONCLUSIONS: For the first time to our knowledge, intraoperative SCEPs were observed for stimulations of the optic radiation and of Meyer's loop. Short latency responses were found in agreement with fast conduction of the visual pathway's connecting myelinated fibers. SIGNIFICANCE: The mapping of the visual pathways was found feasible for neurosurgeries under general anesthesia.
Asunto(s)
Anestesia General/métodos , Potenciales Evocados Visuales/fisiología , Monitorización Neurofisiológica Intraoperatoria/métodos , Microcirugia/métodos , Corteza Visual/fisiopatología , Vías Visuales/fisiopatología , Adulto , Anciano , Estimulación Eléctrica/métodos , Electroencefalografía/métodos , Femenino , Humanos , Imagen por Resonancia Magnética/métodos , Masculino , Persona de Mediana Edad , Nervio Óptico/diagnóstico por imagen , Nervio Óptico/fisiología , Estudios Prospectivos , Corteza Visual/diagnóstico por imagen , Vías Visuales/diagnóstico por imagenRESUMEN
Introduction: A connection clip to the ultrasonic aspirator handpiece was introduced for simultaneous resection and mapping of corticospinal motor tract (CST) (Kombos et al., 2001). Research question: To report retrospectively the use of this clip in cerebral surgery with CST mapping. Material and methods: Eight women and four men were included (mean: 55.8 years, SD 17.3 years). The ultrasonic aspirator handpiece was stimulated every second (5 biphasic pulses, 0.4 âms per phase, max 14 âmA). Motor evoked potentials (MEPs) (Taniguchi et al., 1993), with transcranial and direct cortical stimulation, were alternated with CST mapping. The distances between the stimulus locations to the CST (diffusion tensor imaging based fibre tractography) were determined postoperatively. Muscle strength was evaluated pre-operatively, at discharge and 3 months. Results: Motor mapping thresholds ranged between 2 and 13 âmA, in 12 consecutive patients (7 post-central, 5 insular). The distance of the stimulation site to the CST was fitted (y â= â0.63x+2.33, R2 â= â0.33; x, mA; y, mm), approximating the rule of thumb of 1 âmA indicating 1 âmm (R2 â= â0.22). One patient presented with a deterioration of motor function (wrist, M4+). No intraoperative seizures were observed. Discussion: The concept that 1 âmA corresponds to 1 âmm from the CST, was roughly observed within this low current range. This rule must be applied, integrating the confidence limits, when getting close to the CST, in conjunction with MEPs. Conclusion: The standardization of this clip, for continuous stimulation of the ultrasonic aspirator with simultaneous tissue resection, made the guided surgical flow smoother, more refined and very natural.
RESUMEN
BACKGROUND: Olfactory hallucinations can be part of epileptic seizures of orbitofrontal origin. Olfactory hallucinations, however, are rare and therefore the semiology, localization and lateralization characteristics are underdetermined. In addition, many discrepancies are found in the literature regarding olfactory processing and orbitofrontal (OF) functions and olfactory function. Particularly, the questions of laterality and affective component in coding of odors in the OF cortex remain controversial. AIMS: This study explored whether cortical electrical stimulation of the OF and mesiotemporal brain can trigger olfactory hallucinations with special focus on olfactory percepts in terms of laterality and hedonics. MATERIALS AND METHODS: Eight patients with temporal lobe epilepsy participated in the study, at the time of invasive exploration of their epilepsy. The most distal contact of the OF and anterior hippocampus depth electrodes were stimulated (50â¯Hz, 0.2â¯ms biphasic pulse; maximal stimulation 4â¯mA). Patients were instructed to report any kind of sensation they might experience. Intracranial depth electrodes were localized (iElectrodes): subject-specific brain mask, subcortical segmentation and cortical parcellation based on the Destrieux atlas (FreeSurfer) were superposed to the coregistered T1-weighted MRI and CT images (SPM). The center of mass of each electrode-artifact cluster determined the electrode localization. The electrode labeling was done in patient space. To obtain the electrode coordinates in Montreal Neurological Institute (MNI) space, the images obtained previously in the patient space were first segmented and normalized (SPM). Then, the localization procedure (iElectrodes) was run again with these new normalized images in MNI space. RESULTS: No hallucination was evoked by stimulation, neither of the right nor the left hippocampus (8/8 patients). Pleasant olfactory hallucinations were evoked by OF stimulation in 5/8 patients in either hemisphere. Patients named the percept as the smell of lemon or coffee for example. Among those 5 patients, electrodes were localized in the cortex of the olfactory sulcus, medial orbital sulcus or medial OF gyrus. Increasing stimulation amplitude changed the olfactory percept identification in 3 out of those 5 patients. No affective judgement or change in perceived odor intensity was reported by the patients. No hallucination was evoked by the stimulation of the white matter of the medial OF brain in 3/8 patients independently of the hemisphere stimulated. CONCLUSIONS: This study demonstrated that stimulation of the cortex of the medial OF brain and not of its white matter elicits specific pleasant olfactory hallucinations independently of the hemisphere stimulated, supporting one symmetrical olfactory processing in human.