Comparison of Magnetic Resonance Imaging, Invasive Electroencephalography and Pathologic Findings with Surgical Outcome in Intractable Epilepsy Due to Cortical Dysplasia

Seo, Dae Won; Hong, Seung Bong

Abstract

BACKGROUND: Intractable partial epilepsy is the most frequent manifestation in cortical dysplasia (CD). The surgical removal of the epileptogenic focus in CD is the main therapeutic option for achieving seizure control. However, it is dif-ficult to predict surgical outcome by current diagnostic methods. We investigated 35 subjects with intractable epilepsy due to CD, in order to know the relationship the extent of lesion in a magnetic resonance imaging (MRI), the epilepto-genic foci in invasive electroencephalography (IEEG), pathologic grading, and surgical outcome.
METHODS
We reviewed clinical findings (the seizure history, MRI), IEEG findings (interictal and ictal EEG), pathologic findings and surgical outcomes retrospectively and compared them. All the patients ranged in age from 2 to 45 years (mean: 21.8+10.8years). The time of their seizure onset ranged from 6 months to 31 years (mean:9.4+6.6years). The postopera-tive follow-up period ranged from 7 to 45months (mean:26+14months).
RESULTS
Regarding MRI findings, the lesions were focal (within one lobe) in 10, diffuse (more than one lobe) in 7, and no abnormalities in 18 subjects. The ictal onset zones of ictal IEEG had one focus in 18, two in 7, three in 7, and four in 3 subjects. The area of focus was focal in 15, regional in 14, lobar in 4, and in diffuse areas in 2 subjects. Pathologic grading revealed mild in 18, moderate in 5, and severe changes in 13 subjects. Their surgical outcomes were: Engel's class I in 20, class II in 7, class III in 6, and class IV in 2 subjects. The relationships among clinical features, IEEG, regarding pathology and surgical outcomes, revealed that severe pathologic grading had a significant correlation with earlier ictal onset zones (p=0.003), and diffuse MRI lesions. Diffuse ictal onset zones had poor surgical outcomes (p<0.010).
CONCLUSIONS
Cortical dysplasia may have a diverse pattern of epileptogenic foci in MRI and IEEG. The earlier the seizure onset is, the severe pathologic grading becomes. When the lesions in MRI as well as the ictal onet zones in IEEG were diffuse, the surgical outcome was poor.