The persistent crucial role of the left hemisphere for language in left-handers with a left low grade glioma: A stimulation mapping study

Background: Left-handers have a more bilateral language representation than right-handers. Therefore, in left-handers with a low-grade glioma (LGG) in the left hemisphere (LH), one could hypothesize that the right hemisphere (RH) might allow language compensation, at least partly, with no or only a minor persistent role of the LH in speech. However, although LGG induces language reorganization in right-handed patients, little is known in left-handers. Here, we report the first series of left-handers who underwent awake surgery for a left LGG using intraoperative mapping, in order to investigate whether there was still an involvement of LH in language. Method: Ten consecutive left-handed patients were operated for a left LGG (three frontal, four paralimbic, one parietal, one temporal, one parieto-temporal tumor) using an awake procedure with intraoperative electrical language mapping. Results: Intraoperative language disorders were elicited in all cases but one by electrostimulation in the LH. Cortical language sites were detected in nine cases. Subcortical stimulation also demonstrated the crucial role of left white matter pathways in language, including the inferior occipital-frontal fascicle, arcuate fascicle, lateral segment of the superior longitudinal fascicle and fibers from the ventral premotor cortex. Moreover, stimulation of deep gray nuclei generated language disturbances in four patients. These nine patients experienced transient postoperative language worsening, supporting the persistent critical role of LH in speech. In only one patient, no language deficit was evoked intraoperatively and postoperatively. The ten patients returned to a normal life. Total or subtotal resection was achieved in all cases but one. Conclusions: Our results suggest that, even though the RH may participate in language compensation, the LH in left-handers still plays a crucial role, despite a left slow-growing LGG. Thus, we propose to routinely consider awake surgery for left LGG removal in left-handers patients, to optimize the extent of resection while preserving language.