Abstracts

Rationale: The placement of intracranial electrodes is an integral part of the pre-surgical evaluation of patients with imprecisely defined relationships between lesion and ictal onsets or those where no lesion is visible on imaging. Subdural grid electrodes (SDEs) are used for this purpose at most epilepsy centers in North America. SDE implantation is associated with a not-insubstantial risk of the collection of sympotomatic extra-axial fluid/blood collections (EFC) in adult populations. In most such situations, the electrodes are removed, interrupting the evaluation that was initially planned. We sought to determine if SDEs could safely be left in place after the evacuation of EFC, and subsequently used to plan a resective surgery. Methods: Data were collected for all consecutive adult patients undergoing SDE implantation over a 5.5 year period by the senior author. Demographics, numbers of electrodes implanted, records of prior cranial surgery, hemisphere of implantation, duration of monitoring, and occurrence of bleeding complications or infections were tabulated. Relationships of numbers of electrodes, age, and prior surgery with bleeding risk were all assessed. All patients routinely underwent MR scans at 1.5T and Ct scans post-implantation to assess locations of the SDEs and the presence of EFCs. Results: 65 craniotomies were performed in 60 patients (5 were bilateral) for SDE placement. A mean of 103 electrode contacts (SD 19) were placed, for a mean duration of 9 days (SD 5). Imaging revealed EFCs in almost 70% of cases. In only 4 cases, were the EFCs neurologically symptomatic. In all cases the craniotomy was re-opened, the hematoma and fluid were evacuated, hemostasis was re-accomplished and electrodes were left in situ for subsequent recordings. All 4 of the patients re-operated for EFC underwent definitive resective surgery based on data collected with the same recording electrodes during the same hospital stay. Of the 60, in 2 cases there were concerns for infection that led to premature electrode removal. Neither of these were patients that had symptomatic EFCs Conclusions: The process of implanting electrodes is time and material intensive. We show here that even in cases where EFCs are large enough to produce neurological compromise, they may be removed with the possibility of carrying forth the original plan of obtaining intracranial recordings.