Abstracts

RATIONALE: To determine the relationship between an ictal blood flow alteration identified using subtraction ictal SPECT co-registered to MRI (SISCOM) and the ictal onset zone as defined by intracranial EEG in patients with localization-related epilepsy. METHODS: SISCOM images were analyzed in 25 consecutive patients with intractable partial epilepsy who underwent chronic intracranial EEG recordings and epilepsy surgery between 1998-2000. The mean age was 30.5 years(range, 10-73). In 12 patients (48%) MRI revealed one or more pathological substrates. All patients underwent intracranial EEG studies using subdural grid electrodes for interictal and ictal recordings. Temporal lobe depth electrodes were implanted in 6 patients. The ictal onset zone was extratemporal in 19 patients and restricted to the temporal lobe in 6 patients. RESULTS: SISCOM revealed a localized hyperperfusion alteration in 22 patients (88%). In 17 of the 22 patients (77%) the SISCOM findings were concordant with the site of seizure onset. The ictal onset zone was invariably confined to a selected region of the ictal hyperperfusion zone in the concordant group. In 4 of the 5 discordant patients SISCOM correctly lateralized the epileptogenic zone, but did not localize the area of EEG seizure onset. Seventeen of 22 patients with at least a 6 month follow-up experienced a worthwhile reduction in seizures (Engel Class I-III), and 10 patients were rendered seizure-free. The mean duration of follow-up was 12 months (range, 6-20). CONCLUSIONS: SISCOM may be a reliable indicator of the localization of epileptic brain tissue in patients with intractable partial epilepsy. The SISCOM-identified ictal hyperperfusion zone may prove larger than the area of cerebral cortex participating in the initiation of seizure activity. The SISCOM may also provide a "target" for the placement of intracranial electrodes in selected patients.