Crossed aphasia elicited by intraoperative cortical and subcortical stimulation in awake patients

Abstract

These original findings highlight the possibility of finding crucial cortico-subcortical language networks in the right hemisphere in a subgroup of atypical right-handed patients. These findings provide new insights into the neural basis of language, by underlining the role of the right inferior occipitofrontal fasciculus in semantics and that of the right arcuate fasciculus in phonology, and by supporting the hypothesis of a mirror organization between the right and left hemispheres. The authors suggest that, in right-handed patients, if language disturbances are detected during seizures or on presurgical neuropsychological assessment, especially when right activations are observed on language functional MR imaging, awake craniotomy with intraoperative language mapping should be considered.

The challenge to remove diffuse low-grade gliomas while preserving brain functions

“…Indeed, although language areas are most often identified in the left hemisphere, language sites can also be detected in the right hemisphere, not only in lefthanded or ambidextrous patients [27] but also in righthanders, thus with a risk of crossed aphasia [5,53]. Presurgical functional MRI can help to predict such atypical distribution of language, beyond the calculation of the lateralisation index.…”

“…Indeed, in a patient with a right-side tumour, even if the lateralisation index shows a majority of language activations in the left hemisphere, it does not mean that the minority of language sites activated in the right hemisphere do not correspond to crucial epicentres. Therefore, because of the doubt, awake language mapping should be performed intraoperatively, since functional MRI is not able to differentiate essential regions from areas which can be functionally compensated (and thus removed) [53]. In the same vein, tractography can be useful for the presurgical planning, but this method is nevertheless not reliable enough and can provide only anatomical (and not functional) information about fibre pathways [37].…”

“…The intraoperative mapping of these pathways must be adapted to each patient, for instance by performing awake surgery to detect possible language fibres in the right "nondominant" hemisphere in left-handers or ambidextrous (and even in some cases in right-handers), according to the results of the presurgical neuropsychological examination-namely, if language disturbances have been identified even in cases of left-lateralisation on functional MRI [27,53]. Of note, this list of tracts is not exhaustive.…”

Selection of intraoperative tasks for awake mapping based on relationships between tumor location and functional networks

“…To this end, identifying patient handedness is not enough because crossed aphasia has been reported. 148 Thus, the most important factor in evaluating cerebral dominance is the existence of a preoperative language deficit, even a subtle one, revealed by an extensive neuropsychological examination. Preoperative neurofunctional imaging may also help to assess hemispheric dominance.…”

“…30 Of note, while these findings have been reported mainly for the left dominant hemisphere in right-handed patients, stimulation of the right frontal lobe can also elicit "mirror symptoms" in left-handed and ambidextrous patients, as well as in a subgroup of right-handed patients. 48,148 These perisylvian networks, including the anterior part of the IFOF, both on the right and left sides, appear to be non- resectable-that is, resection should be avoided in order to prevent permanent postoperative deficits. 79 The anterior part of the IFOF represents the deep limit of resection in patients with intrinsic tumors involving the pars orbitalis of the left inferior frontal gyrus or the dorsolateral prefrontal area.…”