Objective:

To enhance the understanding of resting electrocorticography (ECoG) by identifying and categorizing benign variants observed on intracranial electroencephalogram (icEEG)

Background:

Approximately 30% of epilepsy patients have drug-resistant epilepsy, often requiring surgical intervention. Accurate interpretation of icEEG is essential for the success of epilepsy surgery, as benign patterns can mimic epileptiform activity, potentially leading to misidentification of epileptogenic foci. Correctly distinguishing benign variants from pathological patterns is crucial for optimizing resection planning and preserving eloquent cortex.

Design/Methods:

A systematic search of PubMed was conducted to identify human studies reporting benign icEEG patterns published up to August 2021. A total of 5,191 articles were screened using 48 keyword combinations. Exclusion criteria included animal studies (5%), non-EEG modalities (7.4%), purely pathological studies (9.6%), and others (78%). NVivo was used to code and categorize common themes such as high-frequency oscillations (HFOs) and background rhythms.

Results:

A total of 64 studies were reviewed, comprising retrospective (21.3%), prospective (70.3%), and case reports/other designs (6.3%). Data were collected using subdural electrodes/ECoG (40%), SEEG (20%), or a combination of SEEG/ECoG (30%). The studies focused on unique icEEG variants (40%), HFOs (20%), and differentiation of epileptic from physiological patterns. Sleep-related patterns were analyzed in 34% of studies, with physiological findings such as HFOs (40%), ripple activity, and sharp wave ripples. Awake-state benign variants (20%) included mu-rhythms and alpha posterior dominant rhythms (PDRs). Other physiological patterns reported included high voltage 14 & 6 Hz, small sharp spikes, and rhythmic temporal theta bursts of drowsiness. Functional connectivity studies (15.6%) and comparisons with fMRI and MEG (7.8%) emphasized the distinction between benign and epileptiform discharges, aiding in clinical decisions during epilepsy surgery.

Conclusions:

This systematic review provides an atlas of normal icEEG variants that could minimize misinterpretation during epilepsy surgery, reducing unnecessary resections of non-epileptogenic tissue and improving surgical outcomes.