Abstracts

Subdural grids (SDG) have been increasingly used in the evaluation of some patients with pharmacoresistant epilepsy. In a small number of patients the placement of SDG is not followed by a surgical resection. There is a paucity of data about these patients and the causes behind the lack of success in their invasive evaluation. The purpose of this study is to retrospectively review the data on patients who were evaluated at our center with SDG., Adult and pediatric patients who underwent the placement of SDG, followed by prolonged video-EEG monitoring but did not have resective surgery were identified from the Cleveland Clinic database and their medical records were reviewed.
A total of 233 patients underwent SDG placement between January 1997 and June 2005. The placement of SDG and prolonged invasive recordings did not lead to resective surgery in 29 (12%) patients who were included in this review. Mean age was 25 years (7 were [lt] 18 years old). There were 15 males and 14 females. Average duration of seizures was 15 years. The MRI was interpreted as normal in 12 patients, other MRI findings included malformation of cortical development, schinzencephaly and focal brain atrophy. All patients had PET studies and when indicated a Wada test. The number of electrodes used varied between 56 and 160. Average monitoring duration was 8 days (between 4 and 19)., Reasons for NOT pursuing surgical treatment were: a) Identification of multiregional or non-localizable epileptogenic foci (12 pts), b) presence of epileptogenic foci in eloquent cortex (8 pts), c) lack of adequate coverage of the suspected ictal onset zone (5 pts), or d) the lack of seizure recording after SDG (2 pts). In two patients the evaluation was terminated because of surgical complications. Following the SDG evaluation, 6 patients had VNS implanted and 5 others are considering this option. Three patients are considering another invasive evaluation, one had a resective surgery at a later time, and 7 patients are only considering medical treatment., Approximately 12% of patients were not suitable candidates to undergo surgical resection. The two most common reasons were involvement of eloquent cortex and evidence of diffuse epileptogenic zone. It is important to refine or develop better ways to identify this group of patients prior to implantation, such as the use of fMRI, MEG and sophisticated EEG to avoid costly and risky procedures.,