Abstracts

In pre-surgical evaluation of patients with intractable partial epilepsy, ictal SPECT coregistered with MRI has been shown to provide accurate localizing information in search for the epileptogenic region. We report two patients with refractory partial epilepsy from our epilepsy surgery program that had normal MRI scans at primary evaluation. The patients had similar seizure semiology, including peri-oral sensations, impaired speech and tonic posturing of the arms.
The ictal and interictal SPECT image were coregistered using a surface matching technique (Analyze AVW). The images were normalized and the interictal image was subtracted from the ictal image. To measure the statistical deviation from the normal random intensity difference between the images the standard deviation of the difference image was calculated in each cerebral hemisphere (excluding cerebellum), using volumes defined in the MR image and a mass significance (Bonferroni) correction based on a cubic voxel with 7mm side was applied. The SD of the hemisphere with the least variance was used as normal reference.
Patient 1. Subtraction images showed a marked ictal hyperperfusion (5.1 SD) in the left perisylvian region and a mild hyperperfusion in the corresponding region on the right side. Apart from a bilateral hyperperfusion in cerebellum, no other significant hyperperfusion was seen. At a reevaluation of the MR examination after the reconstruction of transaxial MP-RAGE images, areas of cortical dysplasia outlining the Sylvian fissures bilaterally were identified.
Patient 2. Subtraction images showed a hyperperfusion (3.9 SD) in the left perisylvian region and a mild hyperperfusion in the corresponding region on the right side. There was also a hyperperfusion in the left thalamus and a mild hyperperfusion in the cerebellum with right predominance. Reevaluation of the MRI showed mild cerebellar atrophy, but no cerebral pathology.
Our report demonstrates that subtraction ictal SPECT co-registered to 3D MRI improves diagnosis of subtle brain malformations and helps localizing the seizure focus in certain intractable epilepsy patients. The method might help avoiding unnecessary invasive procedures, and thus minimize the risks for complications during pre-surgical evaluation. It can serve as a diagnostic tool for congenital perisylvian syndrome patients with minor perisylvian malformations and mild clinical signs.