Abstracts

Rationale: The juvenile brain is still developing with age. One developmental hallmark in the central nervous system is the maturation of neuronal fibers. Magnetic resonance imaging (MRI) visualizes age-related processes in cerebral white matter, and diffusion tensor imaging (DTI) has recently enabled more quantitative analysis. These changes are mainly believed to represent the process of neuronal fiber myelination. Myelination is not only a morphological change with formation of a myelin sheath around the fiber, but also contributes to functional development by allowing nerve impulses to propagate more rapidly. However, the relationship between these age-related changes on MRI/DTI and neurofunctional development has yet to be elucidated. Transcallosal response (TCR) is an evoked potential study recorded intraoperatively during epilepsy surgery and these waveforms may provide a window into the electrical conduction function of the corpus callosum. Latency of the first positive wave (P1-TCR) represents the conduction time of callosal fibers. This study investigated age-related changes in DTI of the corpus callosum and TCR in patients with epilepsy who underwent corpus callosotomy, and clarified the potential correlations. Methods: These epilepsy surgery program and studies were approved by the institutional review board. Eighty-five patients (51 males, 34 females) between 10 and 504 months of age were reviewed. All patients underwent corpus callosotomy as a surgical option to treat drug-resistant epilepsy, including infantile spasms, Lennox-Gastaut syndrome and other symptomatic generalized epilepsies, and frontal lobe epilepsy. TCR and high-resolution DTI data were available for 77 and 29 subjects, respectively. Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) from preoperative DTI and latency of P1-TCR were plotted against patient age. Correlations were statistically tested with linear or non-linear regression models. Results: Both ADC and FA changed in an age-dependent manner. In particular, ADC decreased with age and mostly plateaued after 100 months of age (R2 = 0.53). Similarly, latency of P1-TCR continuously decreased before 100 months of age and was significantly correlated with age (non-linear regression, p < 0.001, R2 = 0.64). Finally, ADC and latency of P1-TCR correlated significantly with each other (linear regression, p < 0.01, R2 = 0.54). Conclusions: Age-related changes to the corpus callosum as identified on MRI/DTI suggest both morphological and functional maturation of neuronal fibers and may provide a non-invasive means of estimating the developmental age of the brain.