Introduction: Patients with medically intractable focal epilepsy have a variety of underlying pathologies, many of which are surgically amenable. When patients undergo surgical treatment and continue to have seizures, this poses a significant dilemma to the epilepsy management team. There are currently no studies examining the safety and efficacy of subdural grid placement in patients with a history of prior craniotomy.

Methods: We conducted a retrospective review of the medical records of all patients with a prior history of craniotomy for any underlying cause (i.e. trauma, prior epilepsy surgery, vascular pathology, tumor, etc) followed by subdural grid and depth electrode insertion for the evaluation of medically intractable focal epilepsy between 2000 and 2012 at the Cleveland Clinic. In total, 107 patients were included in this study. Information was collected from the medical records regarding patient demographics, medical and surgical history, seizure history, surgical pathology from the index surgery and secondary resection, Engel classification at last follow-up, and complications related to each surgery performed.

Results: The mean age of seizure onset was 15.9 years and mean age for index surgery was 24.2. Three patients began having seizures after the index surgery (two had tumor resections and one had a vascular malformation resected). 100 patients (93%) had no complication associated with the subdural grid placement, and 92 (86%) had no complication after subsequent resection which was equivalent to the index procedure. A total of 48 patients (44%) were Engel Class I (seizure free) at last follow-up.

Conclusions: In patients who have had a prior craniotomy with continuing medically intractable focal epilepsy, further surgical intervention with SDG monitoring does not appear to be associated with increased risk of complications. The seizure free rate in this group appears to be satisfactory and so this may be a viable option in this difficult to treat group.

Patient Care: This research study will aid patients and surgeons in the decision making process regarding whether or not they should undergo repeat craniotomy for insertion of subdural grids and depths. No studies have ever examined this and it is important because reoperation allowed for a 44% rate of seizure freedom in this difficult to treat group.

Learning Objectives: By the conclusion of this session, participants should be able to 1) Describe the difficulties related to Subdural Grid placement in patients with prior craniotomies, 2) Identify patients who are at a higher risk of postoperative complication and 3) Identify patients who are more likely to become seizure free after subdural grid removal.

References: 1) Yuan J, Chen Y, Hirsch E. Intracranial electrodes in the presurgical evaluation of epilepsy. Neurol Sci. 2012 Aug;33(4):723-9. 2) Liubinas SV, Cassidy D, Roten A, et al. Tailored cortical resection following image guided subdural grid implantation for medically refractory epilepsy. J Clin Neurosci. 2009 Nov;16(11):1398-408. 3) Caicoya AG, Macarrón J, Albísua J, et al. Tailored resections in occipital lobe epilepsy surgery guided by monitoring with subdural electrodes: Characteristics and outcome. Epilepsy Res. 2007 Oct;77(1):1-10. 4) Mikuni N, Ikeda A, Takahashi JA, et al. A step-by-step resection guided by electrocorticography for nonmalignant brain tumors associated with long-term intractable epilepsy. Epilepsy Behav. 2006 May;8(3):560-4. 5) Bauman JA, Feoli E, Romanelli P, et al. Multistage epilepsy surgery: safety, efficacy, and utility of a novel approach in pediatric extratemporal epilepsy. Neurosurgery. 2008 Feb;62 Suppl 2:489-505. 6) Kim DW, Kim HK, Lee SK, et al. Extent of neocortical resection and surgical outcome of epilepsy: intracranial EEG analysis. Epilepsia. 2010 Jun;51(6):1010-7. 7) Van Gompel JJ, Worrell GA, Bell ML, et al. Intracranial electroencephalography with subdural grid electrodes: techniques, complications, and outcomes. Neurosurgery. 2008 Sep;63(3):498-505. 8) Vale FL, Pollock G, Dionisio J, et al. Outcome and complications of chronically implanted subdural electrodes for the treatment of medically resistant epilepsy. Clin Neurol Neurosurg. 2012 Nov 3. 9) Wellmer J, von der Groeben F, Klarmann U, et al. Risks and benefits of invasive epilepsy surgery workup with implanted subdural and depth electrodes. Epilepsia. 2012 Aug;53(8):1322-32. 10) Musleh W, Yassari R, Hecox K, et al. Low incidence of subdural grid-related complications in prolonged pediatric EEG monitoring. Pediatr Neurosurg. 2006;42(5):284-7. 11) Blount J, Cormier J, Kim H, et al. Advances in intracranial monitoring. Neurosurg Focus 25 (3):E18, 2008. 12) Johnston JM Jr, Mangano FT, Ojemann JG, et al. Complications of invasive subdural electrode monitoring at St. Louis Children's Hospital, 1994-2005. J Neurosurg. 2006 Nov;105(5 Suppl):343-7. 13) Onal C, Otsubo H, Araki T, et al. Complications of invasive subdural grid monitoring in children with epilepsy. J Neurosurg. 2003 May;98(5):1017-26. 14) Hamer HM, Morris HH, Mascha EJ, et al. Complications of invasive video-EEG monitoring with subdural grid electrodes. Neurology. 2002 Jan 8;58(1):97-103. 15) Vadera S, Mullin J, et al. SEEG Following Subdural Grid Placement for Difficult to Localize Epilepsy. Neurosurgery. 2013 Jan 10.