Abstracts

RATIONALE: The prognosis for seizure freedom following temporal lobe resection is influenced by multiple variables, including seizure localization, MRI findings, results of Wada testing, and possibly the extent of hippocampal resection. There is no clear consensus as to how much of the mesial temporal structures must be resected in order to optimize surgical outcomes. Intraoperative depth electrode recording (IDER) is an electrocorticographic technique that may improve the ability to tailor hippocampal resection and prognosticate seizure freedom following resection.
At the end of this activity, participants should be able to discuss the use of IDER in tailored hippocampectomy and prognosis following epilepsy surgery.
METHODS: All temporal lobectomy patients from 1997 to 2002 were reviewed and patients with IDER were selected. In these patients, following resection of the appropriate temporal neocortex, a depth electrode was placed freehand into the hippocampal region parallel to its long axis. Following a brief recording, it was removed and tissue was resected. The depth electrode was then replaced and recorded from with additional resection performed until no further spikes were seen or no additional resection was possible. Patient outcomes were correlated with the presence or absence of spike activity by IDER at the conclusion of the resection.
RESULTS: 37 patients were identified as having undergone temporal lobe resections with IDER, with one patient lost to follow up. Of the remaining 36 patients, 21 resections were on the right and 15 on the left. There were 14 men and 22 women with an age range of 8-54 years and a mean age of 30 years. The duration of follow up ranges from 3 to 63 months with a mean follow up of 35 months.
24 patients out of the 36 that had IDER had their resections extended beyond the planned resection based upon the result of the IDER. Of these 24 patients, 18 (75%) have a Class I or II outcome (Engel criteria). Of the 12 patients without further extension of the resection, 10 (83%) are Class I or II.
32 (89%) patients had no spike activity at the conclusion of the resection and, of these, 26 (81%) have a Class I or II outcome. Of the 4 patients with continued spikes following the resection, 2 (50%) have a Class I or II outcome.
CONCLUSIONS: Intraoperative depth electrode recording may be a valuable technique for determining the optimal extent of hippocampal resection and the prognosis of seizure outcome in patients undergoing temporal lobe resection for epilepsy. Regardless of the extent of hippocampal resection, these data suggest that it is important to eliminate residual spike activity in the remaining hippocampus for optimum surgical outcome. Further studies of IDER are warranted for better comparison with alternative electrocorticography tehniques.[table1]
[Supported by: The Rosen Fund]