Abstracts

Rationale: Invasive electroencephalography (iEEG) recordings with depth (DE) or subdural electrodes (SDE) are well-established methods to identify the ictogenic area and plan surgical therapy in complex cases of drug-resistant focal epilepsies. Due to their invasiveness, both implantation approaches carry a certain risk of complications, especially bleeding and infection. We aimed to analyze their safety profiles.

Methods: We retrospectively analysed electronical charts of all recordings (n= 452) from patients undergoing invasive presurgical evaluation at the Freiburg Epilepsy Center from 1999 to 2019. Implantation methods included exclusively SDE (n= 156), DE (n= 160) and a combination of both methods (n= 136). The complications were classified as bleeding, infection-associated and other complications and to their clinical manifestation (symptomatic, with transient or persisting sequelae). In addition, possible risk factors (age, duration of iEEG, number of electrode contacts used) for incidence of complications were analyzed.

Results: A total of 18481 SDE and 15439 DE contacts were used for iEEG. The most common complications were hemorrhage related. Symptomatic bleeding with relevant clinically manifestation occurred in a total of 8.2% (11.0% SDE, 1.7% DE, p< 0.0001). Likewise, significantly more SDE explorations required an operative intervention (Evacuation of a hematoma, removal of electrodes or explantation ahead of schedule) due to a bleeding complication (9.9% SDE, 0.3% DE, p< 0.00001). Hemorrhages tended to occur more frequently when using large, 64-contact grids (p= 0.041). In contrast, we found no clear relationship with the number of DE contacts used. Infections occurred in a total of 2.0%. Superficial wound infection occurred in 8 cases (1.9% SDE, 1.9% DE,1.5% combination) and in one case required an electrode removal ahead of schedule. An abscess occurred once (DE), no further intracranial infections were observed. None of the 452 explorations had a lethal consequence. A transient neurological deficit occurred in 8.8% and persisted for at least 3 months in 1.3%. A transient neurological deficit was more common with SDE in conjunction with DE (11.3% SDE, 2.4% DE, p< 0.01). There was no significant difference regarding permanent deficits. Similarly, longer duration of iEEG and age did not significantly affect implantation risks.