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MEG was useful for non-invasive diagnosis of two epileptic foci in one hemisphere of the pediatric patient. Other non-invasive tests, e.g. MRI, SPECT, and VEEG, were inconclusive

Multiple Epileptic Foci

CASE STUDY: Multiple Epileptic Foci

Physician: HIroshi Otsubo, M.D.
Hospital for sick children,
Toronto, Ontario, Canada

Case Study: 

A 15 year-old left-handed male with onset of seizure disorder at 6 years of age. 

Partial seizures were charachterized by tingling in the left arm above the elbow, followed by grasping of left arm with the right hand
 and clonic movements of the left arm and leg. There was no loss of conciousness during the partial seizure, but there was a secondarfy generalization. The seizures were uncontrolled by medication and often occured in clusters lasting several hours, several time per week.

Multisequence unenhanced and gadolinium weighted 1.5 Tesla MR images at age 14 years were reported as normal. Interictal SPECT showed decreased cerebral perfusion in the left posterior-temporal region. SEPs were asymetrical with the contralateral right hemisphere response to leftmedian nerve stimulation delayed 1.3 ms compared to the contralateral response for right stimulation.

Multiple interictal scalp EEGs from ages 6-13 years were nonlocalizing, demonstarting inconsistent paroxysms of spikes and slow waves with either right or left predominance.

Scalp VEEG telemetry at age 14 showed right-frontal onset seizures and interictal bilateral independent spikes and slow waves.

A WADA test showed left-hemisphere dominance for speech and memory.

An MEG study was performed using a Magnes II 74 channel 4-D Nueroimaging susyem at Scripps CLinic in La Jolla, California. Interictal MEG spikes were captured in 6 seconds epochs by an observer who monitored the spontaneous MEG and stimultaniousEEG signals. SEPs from pneumatically-driven stimuli were collected from the fingers, thumbs and lower lips. A single-equivalent dipole model was used to analyze the MEG data.

Two MEG interictal epileptic foci were identified over the right frontal cortex, one over the posterior portion of the middle frontal gyrus and one iover the inferior part of the prerolandic region.
Subdural recordings using grid and strips were performed to confirm the seizure localizations predicted by MEG. The predominant seizure were correlated with spike discharges arising from the right inferior-central region. Prior to the clinical onsetrhythmic spikes and slow waves arose from the posterior oart of the right middle-frontal gyrus. Subdural SEP recording and stimulation was performed to localize somatosensory and motor cortices.

The results of subdural recording percisely confirmed the MEG spike source localizations and SEP MEG source localization.

After the removal of the subdural grid, corticalexcision of the two epileptic zones was performed andmuktiplesubpial transection was performedin the motor face region. There was no functional deficit after the surgery and the patient was seizure free on reduced medications for 2 years since the surgery.


MEG was useful for non-invasive diagnosis of two epileptic foci in one hemisphere of the pediatric patient. Other non-invasive tests, e.g. MRI, SPECT, and VEEG, were inconclusive. The MEG data were used to plan an invasive VEEG study, which confirmed the MEG findings and led to a successful surgery procedure.