ARCHIVED - Improving surgery for epilepsy patients
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July 01, 2011— Ottawa, Ontario
Canadian researchers are developing new imaging techniques to help doctors plan surgery for patients with epilepsy.
About 1 in 200 Canadians have epilepsy, of whom some 30 percent have “intractable epilepsy” — a form that does not respond to medication. For these people, surgery may be the only way to gain relief from debilitating seizures, in which brain cells start to “fire” without control. “Depending on the severity of the disorder, seizures may occur in a particular area or involve the entire brain,” says Dr. Einat Liebenthal, a visiting researcher at the NRC Institute for Biodiagnostics (IBD) in Winnipeg.
Led by Dr. Liebenthal, IBD researchers are working with neurosurgeons at the Health Sciences Centre in Winnipeg to apply non-invasive imaging methods toward pre-surgical planning. The goal is to map any brain areas with key functions that lie near areas where seizures originate. Such maps could improve surgical outcomes by helping surgeons balance the removal of potentially diseased tissue with the risk of neurological deficits from removal of healthy tissue.
The random nature of epileptic seizures can greatly reduce a patient’s quality of life, while putting stress on family members or caregivers. “People with epilepsy are not allowed to drive and they may suffer deficits such as short-term memory loss,” says Dr. Einat Liebenthal.
“If the seizure locus can be identified properly and removed, the patient will come out of surgery free of seizures,” says Dr. Liebenthal. “However, the brain area being resected might have important language or memory functions. Depending on the exact location and the extent of surgery, there might be significant losses in these functions.”
She adds that the precise location of language and memory functions vary from person to person, even in healthy individuals. In most people, language is “left lateralized,” which means it mainly resides in the brain’s left hemisphere. But for some — particularly left-handed people — language functions are spread equally between the two hemispheres or primarily reside in the right hemisphere.
“If a patient has an epileptic focus in the left hemisphere, it is useful to know whether their language is left or right lateralized,” says Dr. Liebenthal. “If it’s right lateralized, this means there is less chance of a serious neurological decline following surgery.”
To map language functions, Dr. Liebenthal’s team is using a combination of functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI). Functional MRI shows which “grey matter” or brain cells are activated when a patient performs a particular language task, while DTI highlights which “white matter” or fibre tracts (connecting different brain regions) are activated. “We ultimately hope to follow about 25 patients before and after surgery,” says Dr. Liebenthal.
Pinpointing the source of seizures
Doctors use different methods to identify the focus of epileptic seizures in a patient. The most common procedure is called video EEG monitoring. For several days, patients are continuously videotaped, while electrodes on their scalp record neural activity. When a seizure is observed on the video, it is matched with data from the electrodes. “This is not a very precise technique for localizing a seizure because the measurement is done on the scalp, while the source of the seizure is inside the brain,” says Dr. Liebenthal.
If necessary, another technique called intracranial EEG may be used. Here, electrodes are placed either deep in the brain or on the surface, depending on the suspected location of seizures. “This technique is much more precise, but it has all the risks of real surgery,” she notes.
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National Research Council of Canada
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