People with refractory epilepsy who are considering epilepsy surgery undergo extensive evaluations to determine the likelihood that any specific surgical procedure will be effective in controlling seizures without unacceptable adverse effects.
Initially, EEG (electroencephalogram) studies are used to determine the origin within the brain of the individual's seizures. The ideal result is for scalp electrode recordings to reveal a consistent origin of the seizures. When this is the case, further tests will determine whether the implicated area (generally the anterior portion of one temporal lobe, or occasionally part of the frontal lobe) can be safely removed without affecting function, such as speech, memory, or fine sensory or motor cortical function.
Neuroimaging tests, including CT, MRI, PET, and SPECT scans, are all extremely valuable in supporting the EEG data, particularly when they provide localizing information that correlates with the EEG findings. However, the information derived from these tests is perhaps most valuable if it points to a possible conflict with the localization of seizure onset suggested by the scalp EEG data. For example, if the ictal EEG shows seizure onset arising from the side opposite a lesion or an area of agenesis or atrophy visible on MRI, that EEG localization may be false.
If the scalp EEG or neuroimaging data leave doubt regarding the side or precise lobe of seizure onset, implanted electrodes may be necessary. Subdural electrodes or stereotaxic depth electrodes may be placed to record more precisely the seizure onset; these special electrodes are physically closer to the cortex, and the origin of the seizure activity, than scalp electrodes.
Surgical intervention may be carried out with a high probability of success if the accumulated data have shown two conditions to be true:
If the person has seizures clearly arising from both sides of the brain, surgical resection is not likely to be of help. In some of these cases, removal of the “most active” or “worst” brain area may lead to increased seizure activity from the remaining site of seizure origin and no overall improvement in seizure incidence. In other, very select cases, this strategy is appropriate. Once again, each case is weighed individually.
Surgical resection of the epileptogenic focus also will not be helpful if the EEG data depict a generalized form of epilepsy onset. Sectioning of the corpus callosum may help patients with generalized seizures, particularly atonic seizures (“drop attacks”).
Reviewed and revised January 2004 by Howard Weiner, MD, New York University.
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