Middle Frontal Gyrus and Area 55b: Perioperative Mapping and Language Outcomes.

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. 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. 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 ( = 0.03). An increased number of gyri with intraoperative positive responses were related with better preoperative ( = 0.037) and worse postoperative ( = 0.029) outcomes. The involvement of the SFG-MFG subcortical area was related with worse language outcomes ( = 0.037). Positive nTMS mapping in the IFG was associated with a better preoperative language outcome ( = 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 ( = 0.031). 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.