Abstracts

Rationale: Stereoelectroencephalography (SEEG) is a relatively newer intracranial technique used for investigation of patients with medically refractory epilepsy. As SEEG is becoming more commonly used for localization of the epileptogenic zone, different rhythms have been recognized. An electrographic rhythm characterized by medium amplitude, 9-11Hz, sharp sinusoidal waves is repeatedly noted in the posterior cingulate electrodes. The aim of this study is to further characterize this rhythm and investigate its significance.  Methods: Between July 2014 and December 2018 at UCI Medical Center, a total of 28 patients underwent implantation of depth electrodes in the posterior cingulate area as part of extensive intracranial coverage to identify seizure onset zone based on presurgical hypothesis. We reviewed their intracranial EEG recordings to characterize a repetitive pattern observed specifically on the posterior cingulate electrodes. Brain MRI studies were used to determine its anatomic location.  Results: A paroxysmal medium amplitude, 9-11Hz, sharp sinusoidal waves rhythm was seen specifically in the lateral contacts of the posterior electrodes in 24 out of 28 patients. It was localized to the pre-central cortex. During the awake state, this pattern was seen intermixed and alternating with beta frequency. The rhythmic pattern was also observed in light sleep, although less frequently and was less well-formed in morphology. Despite standing out from the background, sharply contoured features and paroxysmal nature there was never evolution into a specific ictal pattern. No clinical correlation was seen.  Conclusions: We describe a recurrent rhythm limited to the electrodes in the pre-central cortex. This rhythm does not seem to carry an increased risk of seizures. Recognition of specific patterns in the evolving era of sEEG is helpful for a better understanding of various benign electrographic patterns, and distinction from true epileptiform patterns. Funding: No funding