Abstracts

Rationale: Ictal onset demonstrated on surface EEG does not always correlate with the neuroimaging picture. However, in many Epilepsy Centers these patients are frequently regarded as non-surgical candidates due to the neurologists inability to determine which hemisphere contains the primary focus. We hypothesize that some of these patients who have failed AED therapies are still entitled to surgical intervention, in order to achieve the level of critical EEG recording analysis required, prior to reaching such conclusion. Methods: We report the case of 46 year-old right-handed female who suffered from chronic intractable temporal lobe seizures occurring more than 5 times a day for over 20 years. SPECT showed right temporal hypoperfusion, while language and memory localized to the left posterior temporal region on fMRI. Video EEG monitoring suggested ictal onset in the right temporal region, associated with contralateral rhythmic sharp theta activity at the seizure onset. We questioned whether the left sided theta activity represented the primary seizure focus, although, the rest of the clinical information agreed with the primary focus originating from the right side. To achieve enhanced resolution of the EEG recording, bilateral stereotactic intracranial depth electrodes were placed into the anterior and posterior temporal lobes and the hippocampus.Results: EEG findings are seen in Image 2. Based on these findings, we hypothesized that the right side was likely the primary epileptogenic focus and that both left temporal seizure foci were produced by dispersion, through trans-hemispheric axonal transmission. Stereotactic right frontotemporal craniotomy with anterior amygdalohippocampectomy was performed and the patient experienced significant seizure reduction (x1/months).Conclusions: Secondary epileptogenesis is the progressive process of extension of epileptogenic cortex that occurs through transmission of epileptic bombardment by polysynaptic transmission. Persistently active seizure foci may create a new epileptogenic focus in the contralateral mirror image location. The secondary epileptogenic region is usually broader than the primary epileptogenic region, due to axonal dispersion. Our case supports this theory and demonstrated that clinically useful distinction of the primary seizure focus from the secondary seizure focus can be accomplished using invasive long-term EEG monitoring, but not always through surface long-term video EEG monitoring. Invasive long-term EEG monitoring would likely be useful in cases on unclear laterality. We conclude that invasive, long-term EEG monitoring provides a clearer picture of laterality by offering enhanced analysis of the EEG recording, which should be completed prior to determining non-surgical candidacy , but this requires validation with more cases.