Safety profile of subdural and depth electrode implantations in invasive EEG exploration of drug-resistant focal epilepsy.

Purpose: To analyze the safety profile of subdural and depth electrode implantation in a large monocentric cohort of patients of all ages undergoing intracranial EEG exploration because of drug resistant focal epilepsy diagnosed and implanted by a constant team of epileptologists and neurosurgeons.

Methods: We retrospectively analyzed data from 452 implantations in 420 patients undergoing invasive presurgical evaluation at the Freiburg Epilepsy Center from 1999 to 2019 (n = 160 subdural electrodes, n = 156 depth electrodes and n = 136 combination of both approaches). Complications were classified as hemorrhage with or without clinical manifestations, infection-associated and other complications. Furthermore, possible risk factors (age, duration of invasive monitoring, number of electrode contacts used) and changes in complication rates during the study period were analyzed.

Results: The most frequent complications in both implantation groups were hemorrhages. Subdural electrode explorations caused significantly more symptomatic hemorrhages and required more operative interventions (SDE 9.9%, DE 0.3%, p < 0.05). Hemorrhage risk was higher for grids with 64 contacts than for smaller grids (p < 0.05). The infection rate was very low (0,2%). A transient neurological deficit occurred in 8.8% of all implantations and persisted for at least 3 months in 1.3%. Transient, but not persistent neurological deficits were more common in patients with implanted subdural electrodes than in the depth electrode group.

Conclusion: The use of subdural electrodes was associated with a higher risk of hemorrhage and transient neurological symptoms. However persistent deficits were rare with either approach, demonstrating that intracranial investigations using either subdural electrodes or depth electrodes carry acceptable risks in patients with drug-resistant focal epilepsy.