Abstracts

RATIONALE: Few centers implant intracranial (IC) grids bilaterally in suspected nonlesional extratemporal epilepsy patients (PTs). We reviewed our 8 year experience with this to investigate the utility of this monitoring. METHODS: The pictorial representations of IC electrode placement of all PTs undergoing IC monitoring at Henry Ford Hospital since 1992 were reviewed. Those with overall symmetrical (?20% asymmetry) coverage of at least 2 lobes of each hemisphere and no MRI lesion were selected. Ictal and interictal EEG from noninvasive monitoring (NIM) and intracranial monitoring (ICM) admissions, MRI, surgical status, and postoperative seizure (Sz) outcome were reviewed. For those with hundreds of recorded Sz, representative Sz only were reviewed in detail. Poor Sz outcome was defined as less than 90% reduction of Sz. EEG was reviewed by an individual blinded to surgical status, procedure and outcome. Statistics used were Fisher exact test. RESULTS: 21 PTs met inclusion criteria for this study. A mean of 120.5 electrodes (range 64-162) were placed in each PT. An average of 27 Sz were reviewed for each PT. 12 underwent resective surgery and 9 did not. Of those who underwent surgery, 6 localized to mesial temporal regions and underwent temporal lobectomy (TL). 7 had good postoperative Sz outcomes. Features correlating with undergoing resective surgery and having a good Sz outcome were: unilateral focal spike discharges (DC) on NIM (p=.006), and an IC ictal propagation pattern of slow contiguous spread (p=.003). Features predicting no resective surgery or having a poor Sz outcome were: a NIM ictal pattern of generalized paroxysmal fast or spike DC at onset (p=.02), NIM interictal generalized or bisynchronous epileptiform DC (p=.05), and an IC ictal propagation pattern of noncontiguous spread (p=.003). A trend to better outcome was seen in those who underwent TL (p=.07). CONCLUSIONS: Even with the ability to implant bilateral subdural grid electrodes, nonlesional PTs with generalized or bisynchronous ictal or interictal DC on NIM should be dissuaded from pursuing ICM. Those with focal interictal epileptiform DC from NIM may be encouraged.