Application of magnetic source imaging in localizing the epileptic foci in patients with grey matter heterotopia

Abstract

Objective To evaluate the value of magnetic source imaging(MSI) in localizing the epileptic foci of patients with histologically proved grey matter heterotopia(GMH) and seizure. Methods MSI examinations were performed on 8 patients with GMH and seizure. The location of the epileptic foci defined by MSI was compared with the results of the ECoG. After imaging examinations, all patients received operation with 13-48 months follow up to observe the effectiveness of the operation. Results Among the 8 patients, 1 had hippocampal sclerosis,2 had focal cortical dysplasiaof type Ⅰ B and 1 had focal cortical dysplasia of type Ⅱ B. MRI showed normal findings in 2 cases, subcortical heterotopia in 4 cases, and nodulor heterotopia in 2 cases with one having schizencephaly. The epileptic foci defined by MSI were at right temporal lobe in 2 cases, left frontal lobe in 2 cases, biparietal lobe in1 case, left parietal lobe in 1 case, left temporal lobe in 1 case, and left frontal-parietal lobe in 1 case. The epileptic foci defined by MSI were completely overlaid with area of GMH in 4 cases, closely behind the area of GMH in case, and partly overlaid with area of GMH in 1 cases with size larger than that of the latter. One patient showed two epileptic foci with one located within the area of GMH and the other one 2 centimeters anterior to the area of GMH.One case's epileptic focus located 2 centimeters posteolateral to the area of GMH . The locations of the epileptic foci defined by MSI showed no difference with those defined by ECoG in all patients. According to Engel classification of treatment effect of epilepsy, 6 patients achieved Engle class Ⅰ ( seizure free after operation ), and 2 patients Engel class Ⅳ ( no changes in the frequcenty of occurrence of seizures before and after operation ). Conclusion MSI can noninvasively and precisely localize the epileptic foci before operation in patients with GMH and seizure. Key words: Epilepsy; Magnetoencephalography; Magnetic resonance imging