Seizure Onset Zone and Extent of Resection in Temporal Lobe Epilepsy with Normal MRI
Abstract number :
3.190
Submission category :
Year :
2001
Submission ID :
3099
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
T.S. Walczak, MD, MINCEP Epilepsy Care, Minneapolis, MN; J.R. White, MD, MINCEP Epilepsy Care, Minneapolis, MN; C.M. Cox, MD, Neurosurgical Associates Ltd, Minneapolis, MN; R.E. Maxwell, MD, PhD, Neurosurgery, University of Minnesota, Minneapolis, MN; R.C
RATIONALE: To determine whether resection necessary to remove seizure onset area exceeds resection performed in standard anterior temporal lobectomy (SATL) in patients with temporal lobe epilepsy (TLE) and normal MRI. SATL is an effective treatment for mesiobasal TLE with mesiotemporal sclerosis. SATL is less effective when MRI is normal. In such cases seizure onset zone may extend outside areas resected with SATL. Intracranial ictal EEG may prompt more extensive resction and improve outcome.
METHODS: We identified 13 consecutive patients with normal MRI and scalp EEG evidence of TLE who underwent intracranial EEG monitoring. MRI included 3 mm T1 weighted and fluid attenuated inversion recovery sequences of temporal regions and hippocampus. Electrode arrays included a 32 electrode grid over temporal neocortex and additional subtemporal and orbitofrontal strips. Nine patients with dominant temporal lobe studies underwent language mapping by cortical stimulation. Seizure onset area, anterior margin of language area, and posterior margin of resection were measured from the temporal tip. Seizure onset zone was classified as mesiobasal or neocortical. Extent of SATL was defined as 4.5 cm for left ATL and 5.5 cm for right ATL.
RESULTS: Seizures were recorded in 11/13 patients. Seizure onset area was mesiobasal in 5/11 (46%) of patients, temporal neocortical in 3/11 (27%) both mesio and lateral temporal in 1 (9%), orbitofrontal in 1/11 (13%) and both orbitofrontal and lateral temporal in 1 (9%). Anterior margin of the language area ranged from 7.5 to 9.5 cm from the temporal pole and limited resection in the 1 patient who had the worst seizure outcome. Seizure outcome in first year postoperatively in 10 (3 lost to follow-up) was Engel I - 7 patients, Engel II - 2 patients, Engel III - 1 patient, Engel IV - 1 patient.
CONCLUSIONS: More than half of patients with normal MRI and scalp EEG evidence of temporal lobe epilepsy have a seizure onset area extending beyond the margins of SATL. Intracranial recording defines this area allowing larger resection, and probably leading to improved seizure outcome. Intracranial monitoring should be seriously considered in apparent temporal lobe epilepsy with normal high quality MRI.
Support: MINCEP[reg] Epilepsy Care and NIH-NINDS Grant P50 NS16308