Abstracts

Rationale: To demonstrate how magnetoencephalography (MEG) provides helpful epileptic-focus and functional brain mapping for the presurgical evaluation of patients with frontal tumors and epilepsy, which may obviate the need for invasive Phase II intracranial electrode evaluation. Methods: We report two pediatric cases with frontal tumor-related epilepsy. In case 1, a 16-year-old girl with a nonenhancing left frontal tumor (previously biopsied, with provisional diagnosis dysembryoplastic neuroepithelial tumor (DNET)), electroencephalography (EEG) showed rare focal sharp waves in the left central region during sleep. In case 2, a 12-year-old boy with a well-circumscribed, nonenhancing left frontal cortical tumor, EEG findings showed intermittent focal slowing in the left frontal region. Spontaneous MEG data were collected with a 306-channel Elekta-Neuromag whole-head MEG system, and equivalent current dipoles (ECDs) of interictal spikes were localized. Also, median-nerve somatosensory and auditory evoked responses were localized, and dichotic language hemispheric dominance was determined, using MEG. The spontaneous and evoked ECDs were superimposed on patients brain MRI scans. Results: MEG analysis showed that all interictal spikes were localized to the anterior border of the left frontal tumor in Case 1; and to the posterior-inferior tumor border in Case 2; both with intermittent associated focal left-frontal slowing. Comparing the MEG and EEG results: in case 1, unlike MEG, the EEG could not localize the epileptiform spike activity within the left frontal lobe; and the intraoperative ECoG results were negative for spikes. In case 2, unlike MEG, the EEG did not adequately localize the spikes to the left frontal tumor area. In both cases, MEG showed auditory and somatosensory cortices to be more than one gyrus distant from the tumor; both patients had left-hemisphere language dominance. For both patients, neurosurgery with complete tumor resection was performed after reviewing the MEG results, bypassing phase II EEG. Patient 1 had a final pathologic diagnosis of ganglioglioma WHO Grade 2; and Patient 2 had diagnosis of DNET. The surgical outcomes were good for these two cases, without functional deficits. The patients were seizure-free at postoperative 3 and 6 months, respectively. Conclusions: These case studies show that MEG is a powerful and accurate noninvasive technique which can provide useful information regarding epileptic foci and functional brain mapping for presurgical planning of epilepsy patients with frontal tumors. MEG may be used to bypass invasive phase II EEG for presurgical evaluation of epilepsy patients with frontal brain tumors.