Abstracts

Rationale: MRI negative anterior cingulate epilepsy (ACE) is a rare entity. However, this should be considered in the evaluation of refractory, MRI negative frontal lobe epilepsy since successful localization of the seizure onset zone and subsequent surgical resection can result in long term seizure freedom. Methods: Herein, we describe a case of MRI negative intractable frontal lobe epilepsy where both lateralization and localization were challenging because of electroencephalographic (EEG) surface and intracranial secondary bilateral synchrony, non-contributory semiology and functional imaging. Staged invasive stereotactic depth EEG evaluations were carried out to localize the seizure onset zone. Figure 1. (A) Scalp and invasive left and right electrode recordings of secondary bilateral synchronous ictal discharges are shown. (B) EEG dipole source imaging (performed on a Compumedics Neuroscan system Curry 6.0) suggesting exactly synchronized bi-frontal spikes and shows dipole localization in the midline in a saggital cut. Results: Bilateral stereotactic EEG exploration revealed a very focal, putative ictal onset zone in the right anterior cingulate gyrus as evidenced by high frequency oscillations (250 Hz) and 50Hz low intensity cortical stimulation induced seizures from the same electrode contacts. This was subsequently confirmed through an ILAE Class 1 outcome following resection of the ictal onset and irritative zones. Histopathological examination revealed FCD Type 1b as the cause of epilepsy. Figure 1. (C) A 250Hz high frequency oscillation pattern was seen overriding the sharp wave population arising only from the RB1/RB2 electrodes in the right anterior cingulate region, in the inferior bank of the cingulate sulcus anterior to the genu of the corpus callosum. (D) 50Hz stimulation (0.2ms pulsewidth, 2mAmp intensity) of electrode contacts RB1/RB2, produced the patient's habitual seizure within 2 seconds. Conclusions: Our patient's evaluation and outcome suggests that although rare, MRI negative ACE is an entity that exists. Patients with frontal lobe seizure semiology (hypermotor or prominent gestural automatisms, fearful expression, autonomic signs, palilalic vocalizations), exhibiting secondary bilateral synchrony and non-contributory structural, functional or source imaging, may yet have surgically amenable ACE. Careful SEEG evaluation with additional cortical stimulation for seizure induction provides the best opportunity for a successful outcome.