Bridging surface and depth: A systematic review of seizure patterns in simultaneous scalp and stereo-EEG

Drug-resistant epilepsy often requires invasive monitoring. Although simultaneous scalp EEG and stereo EEG are increasingly used together, their added value for preoperative evaluation and surgical planning remains uncertain and warrants systematic investigation.

We systematically searched PubMed, Scopus and Web of Science for English- or Portuguese-language studies in which patients with drug-resistant epilepsy were simultaneously monitored with scEEG and SEEG. Reports lacking primary data, systematic reviews, conference abstracts, case reports and studies limited to scEEG with electrocorticography were excluded. Two reviewers independently screened all records, extracted data and assessed methodological quality. The protocol was registered in PROSPERO (CRD42024590432) and conducted in accordance with PRISMA-P guidelines.

From 9750 records, 16 articles underwent full-text analysis, and eight retrospective observational studies met the inclusion criteria. These eight studies - evenly split between the United States and Europe - included 250 patients. Data on diagnostic yield and postoperative outcomes were inconsistent. Key findings included (i) detailed mapping of seizure onset and propagation across cortical and subcortical regions, (ii) typical latency intervals between scEEG and SEEG detection, and (iii) concordance rates in localizing the epileptogenic zone.

Simultaneous scEEG-SEEG provides complementary cortical and mesial findings that sharpen the delineation of the epileptogenic zone and allow for targeted surgery. SEEG captures the deep generators, while scEEG provides the broader context for electrode placement. Current evidence is limited to small, methodologically heterogeneous series. Standardized protocols, larger multicenter cohorts and multimodal co-registration are needed to confirm the diagnostic gain and anchor this two-layered approach in routine clinical care.