Language Localization in Multilingual Patients—Evidence From Direct Electrical Stimulation: A Systematic Review and Single Institution Case Series

Abstract

INTRODUCTION: To enable the safe mapping of language function in multilinguals, we need to understand how language organization in multilinguals differ from well-described organizations in monolingual patients. The development and appropriate administration of standardized test batteries intraoperatively is important to ensure accuracy of mapping, as interlanguage differences cannot be accounted by accurate translations alone. Individual or linguistic factors affects language organization. This study aims to review the published literature on language organization in multilinguals and illustrate intraoperative findings from a case series of multilingual patients who underwent language mapping during awake craniotomy at an Asian institution. METHODS: This PRISMA guided review included studies on multilingual patients undergoing awake craniotomy utilizing direct electrical stimulation (DES) to localize language sites during awake craniotomy. Similar details fromcase series ofmultilingual individuals with more than one language mapped at our center, and strategies used to develop intraoperative tasks for non-English languages are also presented. RESULTS: A total of 142 patients in 21 studies were included. These studies included 80.9% bilinguals, 10.5% trilinguals, 6.3% tetralinguals, 2.8% pentalinguals. Most common first languages (L1) are French (26.7%), English (16.9%), Spanish (14.0%), second languages (L2) are English (38%), Spanish (19.7%), Mandarin (7.7%). Our study noted large variation in fluency definition and evaluation methods for language and cognitive evaluation. Stimulation protocols, error definitions were similar. Naming and counting tasks most commonly used. Majority of studies (76.1%) found distinct cortical sites for L1 and L2, and shared sites as well (66.7%). There was no clear relationship between pattern of distribution and age of acquisition, proficiency or nature of language. Sites for specific tasks such as voluntary and involuntary switching, translation, and reading were identified. CONCLUSION: There are distinct differences language organization between multilinguals and monolinguals. It is crucial for understanding of these differences for maximal preservation of each mapped language function to achieve maximal quality of life.