Discrepancies between Preoperative Stereoencephalography Language Stimulation Mapping and Intraoperative Awake Mapping during Resection of Focal Cortical Dysplasia in Eloquent Areas

Abstract

Background/Aims: To compare the reliability of preoperative stereoencephalography (SEEG) and intraoperative electrostimulation regarding functional mapping, and to select the indication for surgery for focal cortical dysplasia (FCD) in language areas. Methods: The authors present the case of a 21-year-old, right-handed female, suffering from chronic pharmacologically resistant epilepsy since the age of 8. MRI showed a subcortical hypersignal on FLAIR and T₂ sequences at the posterior end of the left superior temporal sulcus compatible with an FCD. SEEG invasive monitoring was performed to precisely identify the epileptogenic zone (EZ) and for functional language mapping. Results: The stimulation of the contacts implicated in the EZ through SEEG leads induced language disturbances, which were not reproducible. Surgery was performed under local anesthesia with awake corticosubcortical mapping. Direct intraoperative stimulation in the EZ, including FCD, did not induce language disturbances. Thus, EZ could be removed completely without any postoperative language deficit. Conclusions: The present case suggests that when language disturbances which occur during invasive SEEG functional mapping, in eloquent areas, are not reproducible, resection can be considered using intraoperative electrical mapping, without inducing permanent language impairment. This may be explained by a certain degree of plasticity and reshaping of functional areas associated with a congenital lesion and chronic epilepsy.

Similarities and differences in neuroplasticity mechanisms between brain gliomas and nonlesional epilepsy

“…A new approach could be, for a limited “eloquent” cortical area merging the ictal‐onset zone, to perform a resection leading to an expected neurologic impairment. Then, if the cortical resection is sufficiently limited, and the connectomes preserved, this neurologic impairment, thanks to neuroplasticity, should recover within few weeks or months, as usually seen after low‐grade glioma surgery . However, before adopting such an approach for a purely functional neurosurgery, it is necessary to develop exhaustive knowledge on the probability of recovery based on prelesional investigation, as has recently started to be done in neurooncology …”

Brain mapping in tumors: Intraoperative or extraoperative?

“…Of interest, intraoperative direct electrostimulation is actually the sole technique allowing functional mapping of white matter tracts (in addition to cortical hubs), converse to extraoperative mapping by strip/grid, which in essence is able to investigate only cortex. Furthermore, whereas depth electrodes could arguably provide some functional information concerning subcortical fascicles, a comparison of this technique with intraoperative mapping in awake patient has shown that stereoencephalographic language stimulation mapping was unreliable (Gil Robles et al., ). In addition, in voluminous tumors, the implantation of numerous deep electrodes all around the lesion before resective surgery in order to investigate subcortical connectivity underlying multiple networks surrounding the glioma, seems difficult and impractical.…”

Language mapping using electrocorticography versus stereoelectroencephalography: A case series

“…Extensive case series of the performance of language mapping have been published for ECOG [3], but only single cases [4,5] or case series [6,7] have described the use of language mapping in the setting of SEEG. While these confirm that language deficits can be elicited by DES using SEEG, there exist no comparisons of ECOG and SEEG to determine the relative safety and yield of these modalities.…”