What the neuropsychologist said to the neuroradiologist : two methods of lateralization of landuage in pre-surgical assessment of children with intractable epilepsy

Abstract

For children with intractable epilepsy, surgery provides significant reduction in seizure frequency, with no significant declines in intellectual or behavioral functioning (Datta, et al., 2011). Prior to surgery, children must undergo a thorough assessment to determine the location of the seizure-focus and to evaluate risks of post-operative impairment (Lee, 2010). Currently, fMRI offers one of the most reliable and least invasive means of localizing language prior to surgery (McDonald, Saykin, William & Assaf, 2006). Dichotic listening, a behavioral task in which subjects are asked to listen to two competing stimuli simultaneously, offers a possible alternative for children who cannot complete fMRI studies. Previous studies have relied on research-based listening tasks and the type of quantitative analysis of the fMRI rarely available in the clinical setting. Instead, this study examined how well dichotic listening results predict language lateralization from fMRI within a clinical setting. Data were gathered through a records review of 13 children with intractable epilepsy referred to Austin Neuropsychology through the epilepsy treatment team at Dell Children’s Medical Center. Overall, children classified as atypical language dominance on the fMRI studies showed lower levels of right ear advantage on the dichotic listening measure. Despite this trend, a discriminant analysis using the dichotic listening results to predict fMRI classification showed no significant improvement over chance classification. A secondary analysis examined factors related to a child’s ability to complete an fMRI language study, comparing 12 children from the original sample with 6 children referred through the same process and over the same time period who could not obtain a successful fMRI determination of language lateralization. Overall, children who successfully completed the fMRI language studies showed a trend of lower levels of difficulty with behavioral regulation and higher levels of intelligence. Although the non-significant results highlight the limitations of dichotic listening as a clinical tool, the failure rate within the total sample, along with the information about the roles of intelligence and behavioral regulation, may help spur the development of alternative methods of language lateralization.