Diffusion tensor imaging with tractography to predict memory deficits in patient groups with temporal lobe lesions

Diffusion tensor imaging (DTI) and tractography (DTT) are advanced MRI techniques that enhance the evaluation of white matter microstructure and connectivity. However, their ability to predict cognitive outcomes, particularly memory function in temporal lobe epilepsy (TLE), remains uncertain. This study examined the relationship between tract-specific white matter integrity using DTI/DTT, memory performance, and clinical characteristics in patients with mesial temporal sclerosis (MTS), dysembryoplastic neuroepithelial tumors (DNET), and WHO Grade II gliomas, common etiologies of TLE.

Twenty-four patients with left temporal lobe lesions (8 per group) underwent 3T MRI with DTI/DTT analysis. The Wechsler Memory Scale (WMS-IV) was used to assess verbal and visual memory functions. Associations between memory scores and clinical variables (e.g., age, lesion size, disease duration), as well as imaging measures such as fractional anisotropy (FA) in the ipsilateral hemisphere (side of the lesion) and in memory related pathways, specifically the fronto-occipital fasciculus (FOF), arcuate fasciculus (AF), inferior longitudinal fasciculus (ILF), uncinate fasciculus (UNC), fornix (FX), and cingulum (CI), were evaluated.

Patients with MTS and Grade II tumors showed significantly lower memory performance than those with DNET. MTS patients had smaller lesions and relatively preserved tractography, whereas Grade II tumor patients exhibited more pronounced tract disruption. However, no consistent correlation was found between DTI metrics, as measured by FA in the ipsilateral hemisphere, and memory scores across the cohort. A paradoxical link was found between lower FA in the contralateral hemisphere and better learning and memory scores. DTI/DTT metrics distinguished the groups more effectively; Grade II, DNET and MTS patients differed in the number (Grade II > DNET > MTS) of tracts that showed microstructural changes, and differences in FA measured from FOF, AF, UNC, and CI coincided with worse memory, especially immediate verbal memory and/or spontaneous delayed recall. Nonetheless, individual differences in tract integrity (e.g. in UNC), whilst predictive of changes in cognitive function, did not always distinguish between the patient groups.

These findings emphasize that tractography may have some utility in identifying patients with different etiologies of TLE, but that further research is needed to improve its clinical utility, especially in the prediction of cognitive outcomes in TLE.