Intraoperative mapping of the subcortical language pathways using direct stimulations

Abstract

Functional neuroimaging has improved pre-planning of surgery in eloquent cortical areas, but remains unable to map white matter. Thus, tumour resection in functional subcortical regions still presents a high risk of sequelae. The authors successfully used intraoperative electrical stimulations to perform subcortical language pathway mapping in order to avoid postoperative definitive deficit, and correlated these functional findings with the anatomical location of the eloquent bundles detected using postoperative MRI. At the same time, this also improved knowledge of fibre connectivity. Thirty patients harbouring a cortico-subcortical low-grade glioma in the left dominant hemisphere were operated on whilst awake using intraoperative electrical functional mapping during surgical resection. Language cortical sites and subcortical pathways were clearly identified and preserved in the 30 cases. The anatomo-functional correlations between data obtained using intraoperative subcortical mapping and postoperative MRI revealed the existence in all patients of common pathways which seem essential to language. This was shown by inducing reproducible speech disturbances during stimulations as follows: the subcallosal fasciculus (initiation disorders), the periventricular white matter (dysarthria), the arcuate fasciculus and the insular connections (anomia). Clinically, all patients except three presented a transient postoperative dysphasia, which resolved within 3 months. On control MRI, 14 resections were total and 16 subtotal due to infiltration of functional bundles described above. It is recommended that the combination of the techniques as described could prove ideal for future non-invasive reliable subcortical mapping both in healthy volunteers and in patients harbouring a (cortico)subcortical lesion in order to optimize surgical pre-planning.

Dissociation of subtraction and multiplication in the right parietal cortex: Evidence from intraoperative cortical electrostimulation

“…The large number of stimulation sites was used so that we could study the roles of all the available regions (the inferior parietal lobule, right angular gyrus and superior temporal gyrus) in simple arithmetic. The stimulation-site density was based on previous studies (e.g., Duffau, 2007;Duffau et al, 2002). After locating the tumor boundaries, sterilized paper with printed numbers were placed on the cortical surface to mark the 47 stimulation sites.…”

“…To our knowledge, no study has used the intraoperative cortical stimulation approach to investigate the role of the right parietal cortex in numerical processing. Previous studies only examined the left parietal cortex (e.g., Duffau et al, 2002;Roux et al, 2009;Whalen et al, 1997). Given previous imaging findings of a neural dissociation in the right parietal region mentioned above (Prado et al, in press;Zhou et al, 2007), we expected that subtraction, but not multiplication, would be affected when the right parietal lobe was stimulated.…”

“…Third, intraoperative cortical electrical stimulation (IES) studies also confirmed the importance of the left parietal lobe in number processing (e.g., Duffau et al, 2002;Roux, Boukhatem, Draper, Sacko, & Demonet, 2009;Whalen, McCloskey, Lesser, & Gordon, 1997). The intraoperative cortical electrical stimulation approach is used before the removal of glioma to help doctors avoid dissecting key functional brain regions (e.g., motor, language).…”

“…For example, placing a single electrode on a site in the left inferior parietal region near the angular gyrus, Whalen et al (1997) found that multiplication performance was disrupted much more than was addition performance when stimulation was delivered to the site (27% vs. 87%) (Whalen et al, 1997). Duffau et al (2002) also used intraoperative cortical electrical stimulation and found a dissociation of simple subtraction and multiplication in the left parietal cortex. They found a functional site for multiplication in the inferior part of the AG, a functional site for subtraction in the superior part immediately below the intraparietal sulcus, and a functional intermediary area (overlapping of the two previous sites) for both multiplication and subtraction.…”

Primary progressive aphasia patients evaluated using diffusion tensor imaging and voxel based volumetry-preliminary results

“…The arcuate fasciculus is classically linked to language, and it has been demonstrated that stimulation in different parts of this structure generates different expressions including phonemic paraphasias, and disorders that affect the formation of phonological words 5 . Currently it is recognized that the arcuate fasciculus that connects the parietal and temporal regions of the frontal lobe is composed of various subcomponents.…”