A focal lesion detected by use of magnetic resonance imaging (MRI) is a favorable prognostic
finding for epilepsy surgery. Patients with normal MRI findings and extratemporal lobe epilepsy have
less favorable outcomes. Most studies investigating the outcomes of patients with normal MRI
findings who underwent (nonlesional) extratemporal epilepsy surgery are confined to a highly select
group of patients with limited follow-up.
To evaluate noninvasive diagnostic test results and their association with excellent surgical
outcomes (defined using Engel classes I-IIA of surgical outcomes) in a group of patients with
medically resistant nonlesional extratemporal epilepsy.
A retrospective study.
Mayo Clinic, Rochester, Minnesota.
From 1997 through 2002, we identified 85 patients with medically resistant extratemporal lobe
epilepsy who had normal MRI findings. Based on a standardized presurgical evaluation and review at a
multidisciplinary epilepsy surgery conference, some of these patients were selected for intracranial
electroencephalographic (EEG) monitoring and epilepsy surgery.
Nonlesional extratemporal lobe epilepsy surgery.
Main Outcomes and Measures
The results of noninvasive diagnostic tests and the clinical variables potentially associated
with excellent surgical outcome were examined in patients with a minimum follow-up of 1 year (mean
follow-up, 9 years).
Based on the noninvasive diagnostic test results, a clear hypothesis for seizure origin was
possible for 47 of the 85 patients (55%), and 31 of these 47 patients (66%) proceeded to
intracranial EEG monitoring. For 24 of these 31 patients undergoing long-term intracranial EEG
(77%), a seizure focus was identified and surgically resected. Of these 24 patients, 9 (38%) had an
excellent outcome after resective epilepsy surgery. All patients with an excellent surgical outcome
had at least 10 years of follow-up. Univariate analysis showed that localized interictal
epileptiform discharges on scalp EEGs were associated with an excellent surgical outcome.
Conclusions and Relevance
Scalp EEG was the most useful test for identifying patients with normal MRI findings and
extratemporal lobe epilepsy who were likely to have excellent outcomes after epilepsy surgery.
Extending outcome analysis beyond the resective surgery group to the entire group of patients who
were evaluated further highlights the challenge that these patients pose. Although 9 of 24 patients
undergoing resective surgery (38%) had excellent outcomes, only 9 of 31 patients undergoing
intracranial EEG (29%) and only 9 of 85 patient with nonlesional extratemporal lobe epilepsy (11%)
had long-term excellent outcomes.