Electrophysiologic identification of Broca’s area during frontal lobe tumour surgeries

Introduction: Intraoperative mapping of language function assumes importance in patients undergoing resection of tumours in proximity to Broca’s area. Optimal stimulation protocol for effecting a speech arrest is challenging because of the risk of seizure due to high frequency, long duration electrical stimulation in awake subjects. We report a case series to present our experience with an improvised protocol for direct cortical electrical stimulation for language mapping. Methods: A total of three cases of language mapping have been carried out since the inception (i.e., about 1 month) of neurophysiological monitoring services in our institute. All the patients (two female and one male) had tumours close to the anatomical Broca’s area as determined by pre-operative magnetic resonance imaging (MRI). In one patient, a functional MRI confirmed the same. All were right-handed. Baseline assessment of language function revealed deficits in all the patients. Awake craniotomy was carried out under neuron avigation guidance. Verbal fluency and object recognition tasks were carried out. Stimulation protocol consisted of 1000 ms duration electrical pulse of biphasic polarity presented at 60 Hz for 7 s, repeated intermittently. Results: All patients had language area in the left cerebral hemisphere. Using this stimulation protocol, a current, as small as 5 mA, caused speech arrest and defined the expressive language area. No patient developed intraoperative seizure or did anyone develop new language deficit post- surgery. Conclusion: Our limited experience suggests that our language mapping stimulation protocol has been effective in causing speech arrest without inducing seizures during awake craniotomy for frontal lobe surgeries. Intraoperative language mapping should be considered as the standard of care in such surgeries.

No conflict of interest has been declared by the author(s).