Magnetoencephalography: A Breakthrough Imaging Technique for Pediatrics

Magnetoencephalography (MEG) is an imaging technique that is currently being used before resective surgery in pediatric epilepsy patients to determine whether or not surgery is necessary and if the surgery will be successful. Before this technique was implemented, doctors had to rely on symptoms caused by seizures and traditional techniques that did not provide sufficient information about the success or possible long-term, adverse effects of resective surgery.

Epilepsy affects 1 in 1,000 children every year. Children who suffer from epilepsy are usually prescribed antiepileptic medication to control frequent seizures and have an increased mortality rate due to factors that include neurological deterioration. When medication is not a sufficient treatment for epilepsy, surgery is often required. In the past, surgery was only considered for severe epilepsy cases, but today pediatricians choose resective surgery to treat epileptic children as a means of avoiding long-term consumption of antiepileptic medication. Surgery is also considered for cases where frequent seizures begin to hinder a child’s development or cause encephalopathy (cerebral inflammation).

MEG is a promising technique for the treatment of uncontrollable epilepsy in pediatric patients because it provides noninvasive analysis of the ictal onset zones (IOZ), which are the regions of seizure onset and the functional cortex (motor, sensory, and language regions). A MEG can be used to detect abnormal interictal (period between seizures) brain activity and is particularly useful for locating anatomic lesions that could not be detected by techniques like thin section magnetic resonance imaging (MRI).

Researchers at the Children’s Hospital of Philadelphia recently evaluated the accuracy at which the IOZ and functional cortex could be located by comparing the MEG technique to traditional techniques such as ictal electroencephalography (EEG), interictal EEG, magnetic resonance imaging (MRI), functional cortical mapping, neuropsychological examinations, nuclear imaging, the Wada procedure, and the analysis of clinical seizure symptoms. The results of their evaluation showed that a MEG plays 4 vital roles in the detection of ictal onset zones and the functional cortex:

• The use of a MEG to accurately detect the zones of interest removes the need for long-term intracranial EEG monitoring during epilepsy surgery.
• From a MEG, a doctor can detect bilateral, multifocal, and diffuse ictal onset zones, showing that the pediatric patient should not undergo resective surgery.
• A MEG provides more accurate localization and therefore allows the doctor to make a concrete decision about resective surgery, compared to traditional methods that normally only suggest multifocal ictal activity.
• A MEG allows doctors to locate the eloquent cortex, which is the region of the brain that if removed, causes a loss of sensory and/or linguistic skills. This is an important factor in determining if surgery is required and can be used to avoid damaging this region during resective surgery.

In the future, a MEG may also be used to make decisions such as whether or not surgical procedures like intracranial grid placement or guiding electrode placement are necessary in addition to the detection of lesions that are normally undetectable.

Currently neuroradiologists, neurologists, neurosurgeons, neuropsychologists, and physicists are among the groups of physicians that are involved in guaranteeing that the implementation of MEG for pediatric epileptics is a safe procedure that will allow physicians to more accurately determine which pediatric patients will benefit from resective surgery.

Reference

Schwartz, E., Dlugos, D., Storm, P., Dell, J., Magee, R., Flynn, T., Zarnow, D., Zimmerman, R., Roberts, T. (2008). Magnetoencephalography for Pediatric Epilepsy: How We Do It. American Journal of Neuroradiology. DOI: 10.3174/ajnr.A1029