Abstracts

Rationale: Diffusion tensor imaging (DTI) provides information about magnitude (diffusivity) and directionality (anisotropy) of water diffusion. The arcuate fasciculus (AF) is an important pathway connecting the anterior (Broca) and posterior (Wernicke) language areas. Patients with temporal lobe epilepsy (TLE) often suffer from difficulties with confrontation naming. The purpose of this study was to explore characteristics of DTI measures of the AF in patients with TLE and their relationship to performance on language measures. Methods: DTI was analyzed in 36 intractable TLE patients (22 left, 14 right) and 10 normal controls. All had seizure free outcome after epilepsy surgery. Using DTI Task Card software (Massachusetts General Hospital), a region of interest (ROI) was outlined on one axial slice of the colorized fractional anisotropy (FA) map encompassing fibers of the AF. Fibers passing through the ROI were reconstructed (FA threshold of 0.2, angular threshold 50°). FA and diffusivity (ADC, apparent diffusion coefficient, in x 10 -4 mm2/s) measures in the entire AF were determined. T-tests were conducted to examine differences between left and right AF values among study groups and FA and ADC differences between groups. In addition, correlations between DTI and language measures in the TLE groups were examined. Results: In the control group, there was a trend for higher anisotropy in the left compared to the right AF; ADC values were comparable. In the left TLE group, FA values were comparable; however ADC values were elevated bilaterally compared to the control group. The right TLE group demonstrated significantly higher ADC values and lower FA values in both the left and right AF compared to controls. To explore the functional significance of these findings, correlations were computed between DTI values and language scores. In left TLE patients, FA was significantly positively correlated with semantic fluency in the left AF (r=0.548, p=0.015). No significant correlations were found between DTI measures and language scores in right TLE patients. Conclusions: Diffusivity measures and visualization of tracts allow for better understanding of the pathological changes accompanying TLE. Diffusion measures involving the AF appear bilateral and may evidence damage secondary to seizure spread. Preliminary data suggest a correlation between DTI measures and reduced semantic fluency scores in patients with left TLE. Future studies with larger sample sizes are needed to confirm these findings. B Diehl has been supported by the Milken Family Foundation (Early Career Clinician Scientist Award)