Abstracts

Rationale: Intracranial electroencephalographic monitoring in the presurgical investigation of drug-refractory epilepsy can be performed using stereotactically implanted depth electrodes, or subdural electrodes and grids. At the London Health Sciences Centre Epilepsy Program, the practice has shifted from using subdural to depth electrodes starting in 2013 (Figure). Only a few studies have compared both techniques with respect to feasibility and complications. Methods: Patient characteristics, periprocedural parameters and complications were acquired from a retrospectively-managed databank to compare depth and subdural electrode cases. Results: A total of N=308 intracranial electroencephalographic monitoring cases were analyzed (n=101 depth and n=207 subdural electrodes). Both groups were of equal age (mean 33.8±11 and 32.6±12.4 years) and gender distribution (49.5% and 50.2% male). Patients undergoing stereoelectroencephalography had a mean duration of epilepsy of 18.7±12.4 years, used 2.4±1 antiepileptic drugs, and had a radiological focus in 69/101 (68.3%) compared with 117/207 (56.5%) in subdural cases. A third of the depth electrode patients had previous cranial surgery. On average, implantation of one depth electrode took 14.8±4.6 min (19±7.7 min for one subdural electrode; p 2 per depth electrode (7.3±6 sec and 19.9±16.5 rad*cm2 for one subdural electrode, repectively; p < 0.01). There was no difference in length of stay (12.4±6.6 and 12.7±6.3 days). Complications were generally low in both groups (hemorrhage 3% and 1%; infection 0% and 1.5%, respectively). A permanent neurological deficit was seen in one percent of the patients irrespective of the kind of electrode implanted. Conclusions: For their equal safety profile, good feasibility and high patient acceptance, we prefer stereotactically implanted depth over subdural electrodes at our institution and aim to improve accuracy with our newly introduced stereotactic robot. Funding: None.