Abstracts

RATIONALE: It has been suggested that an optimal seizure outcome depends upon an extensive hippocampal resection. However, large hippocampal resections are not without potential consequences in terms of memory deficits. The aims of this study were: 1) compare seizure outcome following a small medial temporal resection with that following a large medial temporal resection; 2) examine the relationship between extent of medial temporal resection and post-operative changes in measures of material specific memory.
METHODS: 46 patients who underwent temporal lobe resection for medically refractory epilepsy at the University of Washington Medical Center with [gt]1 year follow-up and detailed pre- and post-operative neuropsychological testing were selected for analysis. Tailored temporal lobe resections were performed using intra-operative ECoG, with extent of hippocampal resection determined by the extent of epileptiform discharges recorded directly from the hippocampus. For comparison of seizure outcome, patients were divided into [dsquote]small[dsquote] ([lte]65mm) and [dsquote]large[dsquote] ([gt]65mm) medial resections. For assessment of change in material specific memory, the Weschler Memory Scale-Form I was utilized. Seizure outcome was graded as follows: Class I, seizure free or only a single post-operative seizure; Class II, [gte]75% reduction in seizure frequency; and Class III, [lt]75% reduction in seizure frequency.
RESULTS: There were 24 females and 22 males. Patients[scquote] age at operation ranged from 15 to 54 years, with a mean of 31 years. 26 resections were in the language dominant and 20 resections in language non-dominant temporal lobe. 30 patients had a Class I outcome, with no difference between small vs. large medial resections. Following dominant resection, decline in measures of verbal memory were significantly associated with extent of medial resection (p[lt]0.05). This was particularly the case for patients thought to be most at risk of memory loss i.e. those with normal pre-operative MRI or mild mesial temporal sclerosis. No correlation was seen between extent of resection and visiospatial measures following non-dominant resection.
CONCLUSIONS: Maximal hippocampal resections are not required for a good seizure outcome provided extent of hippocampal resection is tailored to the location of epileptiform discharges recorded from the hippocampus intra-operatively. Smaller resections are associated with less memory loss following dominant resections, particularly in patients most at risk for a post-operative decline in memory.