Computerized brain-surface voltage topographic mapping for localization of intracranial spikes from electrocorticography. Technical note.

The purpose of this paper is to describe the use of computerized brain-surface voltage topographic mapping to localize and identify epileptic discharges recorded on electrocorticographic (ECoG) studies in which a subdural grid was used during intracranial video electroencephalographic (IVEEG) monitoring. The authors studied 12 children who underwent surgery for intractable extrahippocampal epilepsy. Cortical surfaces and subdural grid electrodes were photographed during the initial surgery to create an electrode map that could be superimposed onto a picture of the brain surface. Spikes were selected from ictal discharges recorded at the beginning of clinically confirmed seizures and from interictal discharges seen on ECoG studies during IVEEG recording. A computer program was used to calculate the sequential amplitude of the spikes by using squared interpolation, and they were then superimposed onto the electrode map. Interictal discharges and high-amplitude spike complexes at seizure onset were plotted on the map. This mapping procedure depicted the ictal zone in nine patients and the interictal zone in 12, and proved to be an accurate and useful source of information for planning corrective surgery.

Systematic approach to dipole localization of interictal EEG spikes in children with extratemporal lobe epilepsies.

OBJECTIVES: To assess the reliability of dipole localization based on residual variances (RV), using equivalent current dipole analysis of interictal EEG spikes in children with extratemporal lobe epilepsy. METHODS: Four pediatric patients with extratemporal lobe epilepsy were studied. Digital EEG was recorded from 19 scalp electrodes. Computer programs for spike detection and clustering analysis were used to select spikes. Dipoles were calculated 5 times for each spike using different initial guesses by the moving dipole model. Standard deviation (SD) of the dipole positions was calculated at each time point in the 5 trials. RESULTS: We analyzed the dipoles at 1097 time points from 4 patients. Among 106 time points with RV < 2%, the SD was < 1 mm in 78 (74%), while in those with SD > 1 mm the dipole positions varied between 2.8 and 52.6 mm. Of dipoles with RV < 1%, 26 of 27 (96%) had an SD < 1 mm; the one dipole with SD > 1 mm varied within 2.5 mm. The dipole localizations with RV < 2% corresponded to the epileptogenic zones identified on intracranial invasive video EEG and intraoperative ECoG. CONCLUSIONS: The systematic approach of equivalent current dipole analysis using spike detection, clustering analysis, and an RV < 2% as a standard is useful for identifying extratemporal epileptic regions.

Utility of digital camera-derived intraoperative images in the planning of epilepsy surgery for children.

OBJECTIVE: This study was undertaken to assess the utility of digital camera-derived intraoperative images in the planning of neurosurgery for children with epilepsy. METHODS: A hand-held digital camera was used to capture the exposed surgical field at the time of craniotomy for 11 children with medically intractable seizure disorders. Intraoperative somatosensory evoked potential recordings of phase reversals and direct cortical stimulation were used to map areas of eloquent brain tissue. Digital camera images were obtained to mark regions of functional brain tissue with respect to cortical surface landmarks and subdural grid placement. The digital camera images were then immediately downloaded, in the operating room, to a laptop computer, which was placed next to the electroencephalographic recording device. Using computer software, the epileptologist highlighted the primary and secondary zones of epileptogenesis, as well as the functional brain areas identified during the monitoring period, on the digital camera images on the computer screen. A neurosurgical map was thus created to aid the neurosurgeon and the epileptologist with the proposed cortical resections and multiple subpial transections. RESULTS: With the images obtained using the digital camera, the epilepsy team was able to observe the contacts of the grid electrodes with the brain during the procedure. Color printouts of the images served as references during the period of invasive monitoring. Zones of primary and secondary epileptogenesis, as well as areas of functional brain tissue, were identified and plotted on the digital camera images. Other benefits of the digital camera-derived images included the ability to accurately reposition the grids or letters marking eloquent brain tissue if they were inadvertently shifted during the procedure, the ease with which the images could be obtained and manipulated, the ability to assess postresection epileptiform activity of the surrounding brain tissue with images obtained while an electrocorticographic array was in place, the ability to provide the entire epilepsy team with updated information on the neurosurgical field while minimizing movement in the operating room, and facilitation, with neurosurgical maps, of discussions with the patients and their families concerning proposed cortical resections. CONCLUSION: Digital camera images have become essential components for the planning of cortical resections for children with intractable epilepsy at our institution. We envision widespread application of this technology to other neurosurgical fields.

Interhemispheric interactions analyzed by coherence during flexor spasms.

OBJECTIVE: We used coherence analysis to test for leading discharges on an ipsilateral right mesial temporal lesion in a 5 year old boy with flexor spasms. METHOD: Digital EEG analysis with video-EEG telemetry was performed preparatory to epilepsy surgery. RESULTS: Study of 10 spasms with head drop and subsequent flexion of both arms demonstrated an interhemispheric time lag with secondary bilateral synchrony, with a mean difference of 17 ms. The right hemisphere led. After a lesionectomy with resection of epileptic regions (performed with electrocorticographical guidance), the patient has been seizure-free for 4 years. Pathology confirmed a low-grade mixed glioma and cortical dysgenesis. CONCLUSION: The coherence analysis demonstrated a pathway of secondary generalization, confirming that the lesional side was leading during ictal generalized discharges in flexor spasms.

[A case of hereditary motor and sensory neuropathy with pyramidal tract sign, optic nerve atrophy and mental retardation].

The patient was a 61-year-old man who suffered from gait disturbance since childhood. He also had mental retardation. Gait disturbance was slowly progressive. His mother, sister, brother and son of his sister suffered from gait disturbance. On neurological examination, he showed mental retardation, optic nerve atrophy and neural deafness. He also showed severe muscle atrophy and weakness of bilateral lower limbs associated with pes cavus. Muscle tonus of lower limbs and patellar tendon reflex were increased bilaterally. Achilles tendon reflex was absent. Babinski and Chaddock signs were positive. Superficial and deep sensations were almost normal. There were no cerebellar signs. Blood chemistry was normal. On nerve conduction studies, motor nerve conduction velocity of the upper limbs was normal and that of the posterior tibial nerve was decreased; right 36.0m/sec, left 29.7m/sec. Sensory nerve conduction velocity of the median nerve was slightly decreased; right 36.5m/sec, left 45.2m/sec and sural nerve did not respond to electric stimuli. On sural nerve biopsy, the density of myelinated fibers was severely decreased. Onion bulb formation was not observed. We classified this case as hereditary motor and sensory neuropathy (HMSN) type II based on nerve conduction studies and findings from sural nerve biopsy. HMSN with pyramidal tract sign has been classified as type V and HMSN with optic nerve atrophy as type VI. This case had characteristic symptoms as type V and VI. Histopathological findings of HMSN type V and VI have not been established yet. This case might provide an important clue for classification of HMSN.