Abstracts

RATIONALE: Focal cortical dysplasia (FCD), a neuronal migration disorder, was originally described by Taylor and colleagues. Searching for subtle FCD on magnetic resonance imaging (MRI) is challenging. Patients with a normal MR often need invasive EEG recordings. The intrinsic epileptogenic nature of FCD allows precise localization by magnetoencephalography (MEG) if sufficient epileptic discharges are available. The purpose of the present study is to investigate if MEG increasing the detection of subtle FCD as part of an epilepsy surgery evaluation.
METHODS: Among twenty medically intractable epilepsy patients with migational disordesr and MEG recording, three patients had normal MRIs and histological findings of FCD. Their ages were 6 yrs, 3yrs and 15 yrs. Spontaneous MEG recordings were performed on whole-head MEG system (Magnes WH2500, 4-D Neuroimaging, San Diego, CA). The intracranial locations of electromagnetic events were modeled as equivalent current dipoles (ECD). The dipoles were overlaid on 3D-SPGR MRIs. Their MRIs were evaluated in a standard way and reevaluated with special inspection in limited regions guided by MEG spike localization.
RESULTS: Interictal epileptogenic discharges on EEG and MEG were found in all three patients. Clusters of focal interictal epileptic discharges were localized to frontal (2/3) and central (1/3) areas after overlay on MRIs. In two patients we found tiny focal abnormalities including slightly increased cortical thickness and blurred gray-white matter junction at the locations of interictal events after reevaluation of the MRIs. FCD was confirmed histologically in all patients. All patients are seizure free after surgery.
CONCLUSIONS: MEG can assist in the detection of focal cortical dysplasia. MR images might be reevaluated after MEG recording if they appear normal during standard evaluation
[Supported by: NIH Grant R01 NS37941 to Dr Adrew C. Papanicolaou]