Abstracts

Rationale: Magnetic Source Imaging (MSI) is becoming more widely used for mapping of language cortex in patients being considered for surgical treatment of intractable epilepsy and brain tumors. However, studies investigating the validity of MSI for language mapping typically include data for adults only, and few articles report MSI language data in children 8 years or older (Breier et al. 2001, Papanicolaou et al. 2004). The current study aims to clarify the clinical utility of MSI for language lateralization in children under 8 years of age.Methods: A retrospective record review was conducted of 11 patients ages 4 to 7 years who were referred for MSI at Minnesota Epilepsy Group between 11/04 and 3/07 preliminary to epilepsy or brain tumor surgery. MSI was performed using 148 magnetometers with single equivalent dipole modeling. Intracarotid Amytal Procedure (IAP) and cortical mapping data were reviewed when available.Results: The mean age of children referred for language mapping was 6 years 3 months (range = 4 years 0 months to 7 years 6 months). Two patients were unable to comprehend the task and were not recorded. Of the 9 children who participated in the language mapping task, recordings from 3 (33%) were contaminated by motion artifact and did not yield usable language data. Six children produced clinically relevant data, although one did not follow instructions and the task was modified for another. Four were considered left hemisphere dominant based on MSI activation, while 2 were reported to have bilateral language. Four of the children who completed the language protocol also underwent the IAP. There were no cases in which MSI and IAP were completely discordant. IAP and MSI were in total agreement regarding language laterality in 2 cases (left dominant). One child’s MSI suggested bilateral language, but IAP data indicated left hemisphere language dominance. Subsequent cortical language mapping with a subdural electrode array (SEA) did not identify language functions in the right hemisphere in this patient. The fourth child’s MSI suggested left hemisphere dominance, while bilateral language representation was observed with IAP. Mapping with the SEA confirmed the presence of left hemisphere language. Overall, there was a 75% concordance rate between IAP and MSI in identifying the presence of language in the hemisphere of proposed surgery.Conclusions: In this small sample, 6 of 9 (66%) young children ages 4 – 7 years produced usable language data with MSI. There were no cases in which MSI and IAP language data were completely discordant, and the concordance rate between MSI and IAP for identifying language in the hemisphere of interest was 75%. Results suggest MSI may be a valid method of determining language lateralization in young children. However, IAP and electrical stimulation should continue to play a role in clinical decision making for this population.