Abstracts

Rationale: In a substantial amount of patients undergoing epilepsy surgery there is a need for invasive monitoring using subdural grids, strips and/or depth electrodes. Such monitoring is typically performed 5-10 days. During this period there is often also a need for reducing the antiepileptic drugs (AEDs). Thus there is a risk of surgical complications following the invasive approach as well as a risk due to reducing the AEDs. In the literature severe complications and deaths have been reported. The rationale of this study is to present the complications in Sweden following invasive electrode implantation during the period of 1996-2010.Methods: Data from the Swedish National Epilepsy Surgery register were analysed regarding invasive diagnostic evaluations during the period of 1996-2010. The register includes data from all surgical procedures within the epilepsy surgery programs in Sweden since 1990, and it is prospective from 1995. Data from all patients undergoing evaluation with subdural strips, grids, intracerebral depth electrodes, foramen ovale electrodes or epidural electrodes were analysed. During this period the procedure of SEEG was not performed in Sweden. Two or more electrode types were often combined, and then the most complication prone electrode type was accounted for. Complications are classified as major (persisting after three months and affecting ADL) or minor (resolved within 3 months).Results: During the studied period 865 patients underwent therapeutic surgical procedures where there was also a two-year follow up. 799 of these were resections, the other callosotomies. 276 of the patients underwent invasive monitoring. Five patients had missing data regarding complications. There was no mortality and no major complications. Minor complications occurred in 13 of the 271 patients, (4.8%), most common hematomas (10 ( 3.7%)), seven were subdural hematomas and three epidural hematomas. Two patients had infections, and there was one electrode dislocation. In the group of subdural grids (108 patients) there were 8 (7.4%) complications, mostly hematomas.Conclusions: Invasive evaluation before epilepsy surgery is a valuable and often necessary tool to localize seizure onset zone and the epileptic network for the decision on the optimal surgical resection. However, as every invasive surgical procedure, there is a risk to be considered, also including a mortality following invasive diagnostic procedures. In this prospective, consecutive, national population based series of the invasive electrode procedures in Sweden 1996-2010 the overall complication rate was 4.8 %, all classified as minor. The rate of hemorrhagic complications (3.6%) is comparable to other published data. The most common type (and most dangerous) is the subdural hematoma associated with the use of subdural grids. The absence of major complications, in spite of the potentially serious hematomas, stresses the importance of the neurosurgical surveillance and immediate action such as removing the hematoma, often in combination with removal of the electrodes.