Reduced structural connectivity between sensorimotor and language areas in rolandic epilepsy

Abstract

Introduction: Rolandic epilepsy (RE) is a childhood epilepsy with centrotemporal (rolandic) spikes, that is increasingly associated with language impairment. In this study, we tested for a white matter (connectivity) correlate, employing diffusion weighted MRI and language testing.

Methods: Twenty-three children with RE and 23 matched controls (age: 8-14 years) underwent structural (T1-weighted) and diffusion-weighted MRI (b = 1200 s/mm(2), 66 gradient directions) at 3T, as well as neuropsychological language testing. Combining tractography and a cortical segmentation derived from the T1-scan, the rolandic tract were reconstructed (pre- and postcentral gyri), and tract fractional anisotropy (FA) values were compared between patients and controls. Aberrant tracts were tested for correlations with language performance.

Results: Several reductions of tract FA were found in patients compared to controls, mostly in the left hemisphere; the most significant effects involved the left inferior frontal (p = 0.005) and supramarginal (p = 0.004) gyrus. In the patient group, lower tract FA values were correlated with lower language performance, among others for the connection between the left postcentral and inferior frontal gyrus (p = 0.043, R = 0.43).

Conclusion: In RE, structural connectivity is reduced for several connections involving the rolandic regions, from which the epileptiform activity originates. Most of these aberrant tracts involve the left (typically language mediating) hemisphere, notably the pars opercularis of the inferior frontal gyrus (Broca's area) and the supramarginal gyrus (Wernicke's area). For the former, reduced language performance for lower tract FA was found in the patients. These findings provide a first microstructural white matter correlate for language impairment in RE.

Figure 1. Rolandic connectivity profiles.

The 10% most robust rolandic connections, for which the number of streamlines/voxel >5. Averaged over all subjects, all 4 rolandic regions show high perisylvian connectivity, connecting strongly to the supramarginal and superior temporal gyri. Furthermore, the precentral gyri also strongly connect to prefrontal regions (A, B), whereas the postcentral gyri show strong connectivity with the superior parietal cortex. For the precentral gyri, the interhemispheric difference lies in the transverse temporal gyrus (arrowhead in A); for the postcentral gyri, the differences in connectivity lies in the pars opercularis of the inferior frontal gyrus (arrowhead in C).

Figure 2. Abnormalities in rolandic connectivit.

Only reductions in tract FA were found for patients compared to controls, the most extensive and significant of which were located in the left hemisphere. Especially notice the FA reduction for the rolandic connections with the pars opercularis of the inferior frontal gyrus (white arrowheads in A and C), and the postcentral connection with the supramarginal gyrus (black arrowhead in C).

Figure 3. Association between reduced rolandic connectivity and lower language performance.

In the children with RE, lower tract FA values were significantly correlated with lower core language scores for the connection between the left postcentral gyrus and the pars opercularis of the left inferior frontal gyrus (p = 0.043, Pearson’s R = 0.43). Regression line (solid) and 95% confidence interval (dashed) in black; norm core language score (100) indicated by vertical gray line. FA values were age-corrected.