Rationale Surgery for refractory temporal lobe epilepsy (TLE) relies on concordant laterality between neuroimaging, electrophysiology and neuropsychology. A third of patients have normal MRI scans. In hippocampal sclerosis (HS), widespread abnormalities seen with diffusion tensor imaging (DTI) are more pronounced in the ipsilateral temporal lobe. Could laterality of DTI data help lateralise non-lesional TLE?

Methods DTI scans were acquired in 78 subjects (36 HS, 27 other temporal lesions, 15 non-lesional TLE). Laterality indices for average fractional anisotropy, mean, axial and perpendicular diffusivity in the temporal lobes were calculated and a logistic regression model was used to classify seizure laterality. The model was validated in a previous cohort of 28 subjects (16 HS, five other, seven non-lesional).

Results Laterality indices for each diffusion measure were significantly different between left and right HS groups (p<0.001 for all). The classifier correctly classified the laterality of 35/36 HS, 26/27 other lesions and 12/15 non-lesional patients (overall 94%). Applying this classifier to the previous cohort correctly classified 16/16 HS, 3/5 other lesions and 6/7 non-lesional patients (overall 89%).

Conclusions Laterality indices have been applied to functional MRI data but only more recently to DTI data. Calculation can be automated and may prove a useful clinical tool for presurgical assessment of patients with non-lesional TLE.