Abstracts

Rationale: The use of intracranial EEG monitoring is a valuable tool in the localization of epileptogenic foci prior to cortical resection. Although considered standard of care, little evidence has been compiled regarding the localized reaction of brain tissue to the presence of subdurally placed electrodes, and an extensive literature search revealed only one such published investigation. Insertion of the electrodes is thought to cause mechanical injury to the highly vascular cerebral surface and subdural space, thus triggering an acute inflammatory reaction in response to those injuries as well as the presence of the biomaterial. Conceivably, this reaction may eventually lead to gliosis or localized infection, thus exerting a negative effect upon surgical outcome.Methods: The perioperative records of 24 patients were reviewed, along with the results of pathological examination of resected cortex for the presence of inflammation. Results: Four of twenty-four patients were determined to have evidence of inflammation via pathological evaluation of the resected cortex. The average age of those four was 23, compared to 31.5 for those without inflammation. The mean time of implant for individuals with evidence of inflammation was 3.5 days, and for those without inflammation was 5.4 days. One patient who experienced cortical inflammation went on to develop subsequent localized infection, and five of the 20 without inflammation did so. Finally, both groups experienced varying effects upon seizure outcome after surgery - of the 20 in the non-inflammation group, 5 are seizure free, 11 have experienced a reduction in seizure frequency, and 4 have had no change. Among those who had evidence of inflammation, 1 is seizure free, and 3 report a decrease in the frequency of their seizures.Conclusions: This review of 24 patients demonstrates similar surgical outcomes and infection rates. The time that electrodes were left in place appears to not be a predictive factor in the development of inflammation, and the only obvious difference between groups was the mean age of patients. Data collection is ongoing, but from this small sample, it appears that the presence of inflammation in response to indwelling subdural electrodes is not predictive of resective outcome.