The demonstration of gyral abnormalities in patients with cryptogenic partial epilepsy using three-dimensional MRI

S. M. Sisodiya, J. M. Stevens, D. R. Fish, S. L. Free and S. D. Shorvon
Epilepsy Research Group, Institute of Neurology, London, England.

BACKGROUND: Despite the use of high-resolution magnetic resonance imaging (MRI) in the demonstration of structural abnormalities underlying chronic partial epilepsy, a significant proportion of MRI scans in such cases still appear normal when viewed conventionally as two-dimensional images, especially in extratemporal epilepsies. OBJECTIVES: To increase the yield of MRI in patients with extratemporal epilepsies. To examine specific regions of three-dimensional surface renderings of the cerebral hemispheres. DESIGN: Postprocessing of volumetric MRI data was used to detect abnormalities of gyration that may not be seen otherwise. SETTING: Scans were obtained at a hospital clinical imaging facility. PARTICIPANTS: Sixty-four subjects were studied: 33 controls, 15 patients with hippocampal sclerosis (as disease controls), and 16 patients with cryptogenic partial epilepsy that on clinical grounds was extratemporal. MAIN OUTCOME MEASURES: Gyral patterns were evaluated for abnormality by visual comparison between subjects. RESULTS: Inspection of the routine two-dimensional images had failed to demonstrate relevant underlying neocortical abnormality in any of the patients' scans. Three-dimensional reconstruction revealed abnormal gyral patterns in the frontal lobe convexity in seven of the 16 cryptogenic clinically extratemporal cases. Macrogyria was revealed in one case and increased gyral complexity with altered disposition was seen in six cases. Similar gyral patterns were not seen in any subjects from the other groups. CONCLUSION: Three-dimensional analysis of volumetric MRI data can reveal structural abnormality that is not visible when the data are viewed as two-dimensional images only.