Abstracts

Rationale: Intracranial electrophysiology is an integral part of the pre-surgical evaluation of patients with epilepsy in whom non-invasive evaluations are insufficient. Subdural electrode (SDE) implantation is associated with a not-insubstantial risk of complications including symptomatic extra-axial fluid/blood collections (sEFC). In this study, we aim to report our single center experience in the management of patients undergoing long-term invasive epilepsy monitoring. Additionally, we sought to devise surgical techniques to allow for the evacuation of sEFCs while preserving the SDEs.Methods: A series of 91 consecutive patients who underwent craniotomies for SDE implantation for medically refractory seizures by a single neurosurgeon from 2004-2012 was prospectively analyzed. Technical innovations in electrode array design, and in surgical techniques were implemented in these patients.Results: 108 craniotomies were performed in 91 patients for SDE placement. Identification of the seizure focus occurred in 87 patients (96%) and all of them underwent resection. 48 patients were females (mean age 35 years). A mean of 108 electrode contacts were placed, (mean duration of 7 days). There were six (5.8%) surgical complications. One patient (1%) had permanent mild neurological impairment (mild dysphasia). There was no morality. Four cases of sEFCs occurred, in these cases the craniotomy was re-opened, the EFCs were evacuated, and the electrodes were left in situ. One infectious complication occurred and one patient developed an intra-parenchymal hemorrhage related to a cortical venous injury. Statistical analysis revealed a trend of a five-fold increase in bleeding risk (95% CI 0.75 35, p = 0.1) in patients with prior craniotomies. Conclusions: The risks of SDE implantation can be minimized using various simple surgical strategies including meticulous implantation technique, prolonged sub-galeal drainage and a single electrode cable exit site. We demonstrate that even in cases where EFCs are symptomatic, they may be removed, with the electrodes left in to continue the intracranial recordings