Abstracts

RATIONALE: For localization of epileptic foci in evaluation for surgical resection, ictal single photon emission computed tomography (SPECT) is an established tool and is one of the few noninvasive studies able to localize the Ictal Onset Zone, which has a higher correlation to the Epileptogenic Region. Intracranial EEG recording, the gold standard in seizure localization, is associated with high rates of morbidity and mortality. Therefore, our objective is to determine if ictal SPECT scanning may provide sufficient localizing value to allow patients to avoid the risks of intracranial EEG and proceed directly to resective surgery. After reviewing this presentation, meeting attendees should have a better understanding of the role of ictal SPECT scans in the epilepsy localization process.
METHODS: Ictal SPECT scanning was performed utilizing a standard protocol with injection of 20mCi of 99mTc-HMPA tracer immediately after seizure onset noted clinically or by EEG monitoring. We performed a retrospective review of patients[ssquote] results from their ictal SPECT scans, and where applicable, their intracranial EEG recording, as well as the operative records for those patients who have undergone resective surgery. Post-surgical outcomes after surgery were directly verified by clinic visits and telephone interviews. Our population of 138 patients who were insufficiently localized (by video telemetry, magnetic resonance imaging, FDG-PET scanning, and neurocognitive testing) and were still considered to be surgical candidates underwent ictal SPECT scanning. Of these, 86 had seizures during the recording period, and 79 of these yielded focal results. Twenty-five patients have undergone intracranial EEG monitoring, and results are available for 23.
RESULTS: Lateralization by ictal SPECT correlated with that of intracranial EEG in 17 (74%). Twenty-seven patients have gone on to resective surgery, of which outcomes are known in 22. The lateralization of the SPECT focus and the site resected correlated in 19. Follow up information is available for 15 of those patients. Ten are seizure-free (Engel Class I), and three have had a significant reduction in their seizure frequency (Engel Class II and III), yielding a sensitivity of 77% and a specificity of 60%. Conversely, results are available for 22 of the 24 patients who underwent both ictal SPECT and intracranial EEG. Surgical outcomes are available for 10 of those patients who underwent resection based on the results of intracranial EEG; six are seizure free, and one is Class II/III (Sensitivity 79%, Specificity 70%). Finally, six patients proceeded to surgery without intracranial monitoring; in five of the patients, the SPECT localization was that of resection. Of those five patients, four (80%) are seizure-free, and the fifth has noted a marked reduction in the frequency of her seizures.
CONCLUSIONS: Ictal SPECT displays comparable sensitivity and specificity to intracranial EEG and can accurately predict the ictal onset zone in some patients and may have obviated intracranial EEG. Further studies are necessary to determine which subsets of patients can proceed to surgery based on ictal SPECT findings.