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Ribenis, Aksels (2009): Epilepsy surgery around language cortex: A study with indepth discussion of cortical stimulation mapping as a gold standard for detecting language cortex and a comparison of two different cortical mapping techniques to ensure postoperative language function and seizure control in this group of epilepsy surgery patients. Dissertation, LMU München: Faculty of Medicine
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Abstract

Background. Both epilepsy surgery and surgery close to functionally significant cortical areas have challenged neurosurgeons in the last two decades. With this work we wanted to illustrate the current status of epilepsy surgery close to language cortex in our clinic (Neurosurgery Clinic, University of Munich) and to evaluate our tactic of repeated intra-operative language mapping after initial extra-operative language mapping in cases, where language areas lie very close to or overlaps with the epileptogenic zone. First part of this work describes the process of decision making in epilepsy surgery – patient admission criteria, gradual investigational process from non-invasive to invasive. The main emphasis is put to the analysis of invasive language mapping (extra- and intra-operative) as this is the current gold standard of language localization in neurosurgery. Here the historical development of language mapping, together with its physical and physiological concerns is discussed. The next part of this work is devoted to the analysis of two different invasive language mapping tactics – extra-operative versus combined extra- and intra-operative mapping. Methods. Group of retrospective (19) and prospective (3) patients, operated in our clinic in time period from 1997 to 2007, was gathered. Among these 22 patients were 11 male and 11 women with a mean age of 31,9 years and mean epilepsy duration of 16,3 years. Only those patients, by whom either by extra-, intra-operative or both stimulation methods a language cortex close to or overlapping with epileptogenic zone was found, were included in our study. The patients were divided in 2 groups, basing on the language mapping tactic, used during the investigation. Only extra-operative language mapping was used in cases, where rather safe distance (more than 10 mm) between language sites and epileptogenic zone was seen (Ex-M group). The necessity for additional intra-operative language mapping was seen in cases, where rather small (less than 10 mm) distance between language sites and epileptogene cortex or overlapping of both zones was seen (Co-M group). Results. Only extra-operative language mapping was used for 8 patients and the combination of both language mapping techniques was used in 12 cases. In 1 case language was mapped by functional magnetic resonance and in 1 case – only intra-operatively. All patients underwent resective operations. Immediate post-operative language deterioration was seen only in 10 (45,4 %) cases (6 (75%) cases in Ex-M sub-group and 4 (33,3%) in Co-M sub-group) out of the whole group. In 2 cases (1 in each group) the language deterioration was permanent (detectable also 6 months after surgery). The patient in the Co-M sub-group had permanent language deterioration already pre-operatively. Thus the only new permanent post-operative language deterioration was seen in 1 case of Ex-M sub-group, where rather safe distance between language and epileptogenic zone was thought pre-operatively. Regarding seizure outcome, patients were evaluated for at least 2 years (mean follow up 46,6 months). The results were gathered from 18 patients (only retrospective patients) and were as follows: Engel I – 9 cases (50%), Engel II – none, Engel III – 2 (11,1%) cases, Engel IV – 7 (38,9%) cases. In 9 unfavourable seizure outcome cases (combination of Engel class III and IV cases) apparently no full resection of the epileptogene zone was achieved. In 5 cases this was known already intra-operatively, in the remaining 4 cases it was noted during the follow up period. In 8 of these cases the reason for incomplete resection of the epileptogene zone was its close relationship or overlapping with speech cortex and/or difficult localization of the epileptogenic zone. In 1 case complete resection could not be done due to intra-operative complications. In the Co-M sub-group (n=9) the results were following: Engel I – 3 (33,3%) cases, Engel II – none, Engel III – 1 (11,1,%) case and Engel IV – 5 (55,6%) cases. In the Ex-M sub-group (n=7), the results were following: Engel I – 4 (57,1%), Engel II-none, Engel III – 1 (14,2%), Engel IV – 2 (28,7%) cases. No statistically significant differences were observed between both groups regarding immediate post-operative language deterioration, new persistent language deterioration and Engel class I outcome.

Abstract

Conclusions. Apart from casual neocortical epilepsy surgery, neocortical surgery close to speech areas identifies the need for language mapping in order to state safe resection borders. The long term post-operative results regarding language outcome in our study are satisfying and justify the use of invasive language mapping as the best language localization method. As no statistically significant differences regarding language outcome are seen in comparison of both groups, we can conclude that both invasive language mapping tactics can be successfully used in epilepsy surgery. However, the use of combined extra-intra operative language mapping is associated with better post-operative language outcome. Here we can appraise our indications for combined language mapping to be considerable at least for cases where significant tradeoff (distance of less than 10 mm) between epileptogenic and language areas is seen. Also seizure outcome is found not to be significantly influenced by use of one or another language mapping technique. Better post-operative results are seen in cases, where less significant conflict between both cortical areas is seen and thus somewhat more aggressive resections of the epileptogenic zone are possible. The post-operative results regarding seizure control in the whole group of epilepsy surgery close to speech areas can be seen as satisfactory, taking into account the complex pathology of these patients. A complete seizure freedom is seen in 50% of cases. The main reasons for unfavourable seizure outcome were significant conflict between full resection of the epileptogene zone and preservation of safe distance from speech cortex together with difficult localization of the epileptogene zone. Finally, we can conclude that epilepsy surgery close to speech cortex is a very complex treatment method. The complexity is based on the diversity of patient characteristics, localization of the epileptogenic zone and language sites. However, with the use of vast investigational techniques and gathered experience, it is possible to achieve good post-surgical results. We would also like to advocate a need for similar study with larger number of patients. This could provide more significant analysis of both language mapping tactics in epilepsy surgery close to speech areas.