Intraoperative motor speech mapping under general anesthesia using long-latency response from laryngeal muscles

The aim of our study was to determine any association between preservation of long latency response evoked by electrophysiological mapping of the caudal part of the pars opercularis (inferior frontal gyrus Broca area) and postoperative speech function after tumour removal in patients under general anesthesia.

Twelve native Turkish-speaking patients with tumors in the dominant left frontal lobe, near the Broca area, were included in a single-center prospective cohort study. Hooked-wire electrodes were placed in both cricothyroid muscles (CTHY) before anesthesia and a monopolar electrode was used to stimulate the caudal portion of the pars opercularis of the inferior frontal gyrus before and after tumor removal. A long latency response (LLR) elicited at the contralateral (CTHY) muscle was interpreted as a positive stimulation of the Broca area. Patients received one pre-op and two post-op cognitive assessments. The Montreal Cognitive Assessment (MoCA) was used to assess global cognition and a "Cookie Theft" picture description task from the Boston Diagnostic Aphasia Examination test was used in assessing the language functions.

Electrical stimulation elicited a long latency response (LLR) in 9 (75 %) out of the 12 patients. The mean latency of the LLR was 50 ± 11 ms. Four (33.3 %) of the 12 patients showed temporary impairment in fluent speech postoperatively and all had full recovery during the 3-month follow-up period.

The use of electrophysiological mapping methods by using EMG recording from laryngeal muscles may help to identify the opercular part of the Broca area under general anesthesia in order to preserve fluent speech functions.