Abstracts

RATIONALE: Subdural grid cortical stimulation is often used to identify eloquent cortex prior to resective epilepsy surgery. However, the procedure is time-consuming when proceeding one or two electrodes at a time. The current study examined the safety of stimulating more than two electrodes simultaneously in order to permit later multiple-contact stimulation.
METHODS: Patients undergoing right standard anterior temporal lobectomy (n=5) consented to the current study. A subdural grid was placed on the anterior temporal lobe to be resected after a standard craniotomy under general anesthesia. Bipolar stimulation using a Grass Instruments S12 stimulator (5s, 50 Hz, 0.3ms waveform) was conducted. Amperage was increased from 2 to 14-15ma with other contacts on the grid assessing afterdischarges. After the bipolar stimulation, 4-6 contacts were stimulated simultaneously (in parallel) referenced to one of the same contacts as in the bipolar stimulation. Amperages were increased from 2 to 14-15ma. The 4-6 contacts were stimulated for 15 minutes, with 5 seconds of stimulation alternating with 5 seconds of rest to assess afterdischarges. Following the stimulation, the anterior temporal lobe was resected en bloc. The resected specimen was stained with indigo carmine ink at sites where simultaneous stimulation had occurred, and at two sites where no stimulation occurred. The specimen was sent to a neuropathologist who performed histologic analysis of the specimens blinded to which sites had been stimulated. Histologic data were collected on stimulated vs. non-stimulated sites.
RESULTS: Histology showed routine superficial subpial (chaslin) gliosis and sommer[scquote]s sector gliosis in the resected temporal cortex. Four of the five patients showed no histologic abnormalities at sites underlying the contacts stimulated simultaneously. One patient showed small, acute, superficial intracortical infarcts with neuronal and glial shrinkage, pyknosis and hypereosinophilia at 2 of the 6 contacts stimulated simultaneously. However, sites underlying contacts where no stimulation had been applied showed similar small infarcts, suggesting that placement of the subdural grid on the cortex rather than the stimulation resulted in the histologic changes.
CONCLUSIONS: Simultaneous stimulation of up to 4-6 subdural grid contacts does not result in significant histological changes. These findings indicate that simultaneous stimulation of multiple subdural grid contacts may be performed without damaging underlying cortex.