Abstract
Anterior temporal lobe resection (ATLR) is an effective treatment for refractory temporal lobe epilepsy (TLE). Widespread abnormalities in diffusion parameters involving the ipsilateral temporal lobe white matter and extending into extratemporal white matter have been shown in cross-sectional studies in TLE. However longitudinal changes following surgery have been less well addressed. We systematically assess diffusion changes in white matter in patients with TLE in comparison to controls before surgery and look at the longitudinal changes following ATLR at two timepoints (3–4 months, 12 months) using a whole brain approach.We find predominantly unilateral baseline changes in temporal and extratemporal structures compatible with altered myelination (reduced fractional anisotropy, increased mean and radial diffusivity). Following surgery, these changes progress in efferent tracts from the resected temporal lobe compatible with Wallerian degeneration. However more superiorly in the corona radiata, internal and external capsules and nearby tracts, changes compatible with plasticity are observed (increased fractional anisotropy and axial diffusivity, reduced radial diffusivity).There is little progression between 3–4 months and 12 months following surgery in patients with left TLE, but the changes become more widespread in patients with right TLE suggesting that plasticity occurs more slowly in this population. The neuropsychological correlates of such plasticity should be explored further.
Highlights
Temporal lobe epilepsy (TLE)1 is the most common cause of refractory focal epilepsy with up to 40% of patients refractory to medication (Semah and Ryvlin, 2005)
More limited increases in mean diffusivity (MD) were observed in the left hemisphere including the fornix, internal and external capsules, uncinate fasciculus (UF), inferior longitudinal fasciculus (ILF), inferior frontooccipital fasciculus (IFOF) and corpus callosum (Supplementary Fig. 2, Supplementary Table 1)
In patients with right TLE, there were widespread reductions in fractional anisotropy (FA) compared in controls
Summary
Temporal lobe epilepsy (TLE) is the most common cause of refractory focal epilepsy with up to 40% of patients refractory to medication (Semah and Ryvlin, 2005). Anterior temporal lobe resection (ATLR) is an established and effective treatment (Wiebe et al, 2001). Crosssectional white matter changes in TLE have been extensively studied but longitudinal changes following surgery have been less well addressed. Diffusion tensor imaging (DTI) enables the non-invasive assessment of white matter structure (Basser, 1995) and is ideally suited for both cross-sectional and longitudinal studies. Widespread abnormalities in diffusion parameters have been demonstrated in patients with TLE not.
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