Abstracts

Subtraction Ictal SPECT Co-registered to MRI (SISCOM) improves the determination of the epileptogenic zone in patients with neocortical epilepsy. However, there are very few studies that have compared SISCOM with intracranial ictal EEG localization. In this study, we compared the relationship of the SISCOM focus with that of intracranial EEG localization by utilizing 3-dimensional (3D) volumetric brain maps with co-registered SISCOM and intracranial electrode images. Postsurgical outcome in these intractable neocortical epilepsy patients was also assessed.
Patients with neocortical epilepsy who underwent SISCOM studies and intracranial EEG monitoring were retrospectively reviewed. The 3-D volumetric brain maps with co-registered SISCOM and intracranial electrode images were constructed utilizing the Analyze software (Mayo Foundation). The images were reviewed in a blinded fashion separate from the clinical history, video-EEG findings, and post surgery outcome. The Seizure Frequency Scoring System was used to quantify pre-surgical and postsurgical seizures. Excellent outcome was defined as postsurgical score of [le]4 (seizure-free, auras only, or less than 3 nocturnal seizures per year); whereas favorable outcome was defined as an improvement of [ge]2 points ([gt]75% reduction in seizure frequency).
Eighteen patients were identified (8 males, 10 females), with a mean age of 27.9[plusmn] 14.7 ([plusmn] 1 SD) years. Mean duration of epilepsy at presentation was 18.7[plusmn] 11.4 years. No lesion was found in the MRI of 10 patients. The intracranial EEG seizure started from electrodes overlying the SISCOM focus in 10 (56%) patients, and in the vicinity (within 3 cm) of the SISCOM focus in another 3 patients. Amongst 5 patients with discordant findings, the intracranial EEG seizure commenced in the same lobe as the SISCOM focus in 4 patients. Concordance between the SISCOM focus and the intracranial EEG did not vary according to the timing of the ictal SPECT injection or the presence of MRI lesion. Resective epilepsy surgery was performed in 15/18 patients. The SISCOM focus was resected in all but two patients. Ten patients had one year or longer post-operative follow-up. Outcome was excellent in 5, favorable in 3, and poor in 2 patients.
The SISCOM focus and the intracranial EEG seizure focus are generally concordant in majority (72%) of intractable neocortical epilepsy patients. Further study is needed to assess the effect of the concordance vs. the extent of surgical resection on the outcome of resective epilepsy surgery.