Abstract
Background: The simplistic approaches to language circuits are continuously challenged by new findings in brain structure and connectivity. The posterior middle frontal gyrus and area 55b (pFMG/area55b), in particular, has gained a renewed interest in the overall language network.Methods: This is a retrospective single-center cohort study of patients who have undergone awake craniotomy for tumor resection. Navigated transcranial magnetic simulation (nTMS), tractography, and intraoperative findings were correlated with language outcomes.Results: Sixty-five awake craniotomies were performed between 2012 and 2020, and 24 patients were included. nTMS elicited 42 positive responses, 76.2% in the inferior frontal gyrus (IFG), and hesitation was the most common error (71.4%). In the pMFG/area55b, there were seven positive errors (five hesitations and two phonemic errors). This area had the highest positive predictive value (43.0%), negative predictive value (98.3%), sensitivity (50.0%), and specificity (99.0%) among all the frontal gyri. Intraoperatively, there were 33 cortical positive responses—two (6.0%) in the superior frontal gyrus (SFG), 15 (45.5%) in the MFG, and 16 (48.5%) in the IFG. A total of 29 subcortical positive responses were elicited−21 in the deep IFG–MFG gyri and eight in the deep SFG–MFG gyri. The most common errors identified were speech arrest at the cortical level (20 responses−13 in the IFG and seven in the MFG) and anomia at the subcortical level (nine patients—eight in the deep IFG–MFG and one in the deep MFG–SFG). Moreover, 83.3% of patients had a transitory deterioration of language after surgery, mainly in the expressive component (p = 0.03). An increased number of gyri with intraoperative positive responses were related with better preoperative (p = 0.037) and worse postoperative (p = 0.029) outcomes. The involvement of the SFG–MFG subcortical area was related with worse language outcomes (p = 0.037). Positive nTMS mapping in the IFG was associated with a better preoperative language outcome (p = 0.017), relating to a better performance in the expressive component, while positive mapping in the MFG was related to a worse preoperative receptive component of language (p = 0.031).Conclusion: This case series suggests that the posterior middle frontal gyrus, including area 55b, is an important integration cortical hub for both dorsal and ventral streams of language.
Highlights
Previous models of parcellation of the cerebral cortex have been proposed based on cytoarchitectonic [1, 2], myeloarchitectonic [3, 4], or functional characteristics of the different cerebral cortical areas [5, 6].More recently, a new mapping of the human cortex has been described, using a multi-modal gradient-based parcellation approach [7]
High-grade gliomas were prevalent in this series [71% World Health Organization (WHO) grade III and IV]
Previous studies have implicated the role of posterior middle frontal gyrus (MFG) and area 55b in language [7, 9, 10]
Summary
Previous models of parcellation of the cerebral cortex have been proposed based on cytoarchitectonic [1, 2], myeloarchitectonic [3, 4], or functional characteristics of the different cerebral cortical areas [5, 6].More recently, a new mapping of the human cortex has been described, using a multi-modal gradient-based parcellation approach [7]. Previous models of parcellation of the cerebral cortex have been proposed based on cytoarchitectonic [1, 2], myeloarchitectonic [3, 4], or functional characteristics of the different cerebral cortical areas [5, 6]. It has been described to be involved in various language production tasks and fluency of speech [7, 9, 10]. These findings are responsible for the renewed interest in the contribution of the posterior MFG to the overall language network. The posterior middle frontal gyrus and area 55b (pFMG/area55b), in particular, has gained a renewed interest in the overall language network
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