High‐resolution hippocampal diffusion tensor imaging of mesial temporal sclerosis in refractory epilepsy

Abstract

We explore the possibility of using diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) to discern microstructural abnormalities in the hippocampus indicative of mesial temporal sclerosis (MTS) at the subfield level. Methods:We analyzed data from 57 patients with refractory epilepsy who previously underwent 3.0-T magnetic resonance imaging (MRI) including DTI as a standard part of presurgical workup. We collected information about each subject's seizure semiology, conventional electroencephalography (EEG), highdensity EEG, positron emission tomography reports, surgical outcome, and available histopathological findings to assign a final diagnostic category. We also reviewed the radiology MRI report to determine the radiographic category. DTIand NODDI-based metrics were obtained in the hippocampal subfields.Results: By examining diffusion characteristics among subfields in the final diagnostic categories, we found lower orientation dispersion indices and elevated axial diffusivity in the dentate gyrus in MTS compared to no MTS. By similarly examining among subfields in the different radiographic categories, we found all diffusion metrics were abnormal in the dentate gyrus and CA1. We finally examined whether diffusion imaging would better inform a radiographic diagnosis with respect to the final diagnosis, and found that dentate diffusivity suggested subtle changes that may help confirm a positive radiologic diagnosis. Significance:The results suggest that diffusion metric analysis at the subfield level, especially in dentate gyrus and CA1, maybe useful for clinical confirmation of MTS.

Morphometric and microstructural characteristics of hippocampal subfields in mesial temporal lobe epilepsy and their correlates with mnemonic discrimination

“…This damage would be greatest in the DG, which is postulated to be the most affected structure in MTLE-HS ( 58 ). A recent study reported similar results ( 35 ).…”

“…On the contrary, in the part of the MST task assessing general recognition memory (i.e., discrimination between studied and novel items), their performance did not differ from controls ( 33 ). The aim of our study was to characterize microstructural abnormalities in each of the hippocampal subfields in these patients ( 35 ) and, for the first time, to determine the relation of these metrics with their mnemonic performance on a behavioral pattern separation task.…”

“…In the current study, our objective was to test the hypothesis that the integrity of certain hippocampal subfields, DG and CA3, would be more associated with mnemonic discrimination performance. With this aim, we sought to characterize not only the atrophy (volume loss) but also the microstructural organization of the hippocampus at the subfield level by using multimodal MRI data from patients with MTLE-HS to reveal novel features of the hippocampal anomalies ( 35 ). Microstructural features will be described using four diffusion MRI-derived metrics obtained from the spherical mean technique (SMT), and hippocampus subfield volumes will be automatically computed from T1-weighted images.…”

“…To our knowledge, there are no studies describing how changes in the hippocampal subfield microstructure are related to patients with memory functioning MTLE. The novel use of diffusion analysis by tissue compartment could help deepen our knowledge of the pathophysiology of the disease to a neuronal level ( 35 ) and to better understand how the damage in these structures is contributing to the mnemonic problems in these patients. Moreover, analyzing the volumetric and microstructural changes in the subfields of patients with left and right MTLE-HS using MRI could help us to confirm the different susceptibility patterns of the two groups.…”

Neurological update: structural and functional imaging in epilepsy surgery

“…DTI can also better inform us about radiographic diagnoses such as mesial temporal sclerosis (MTS), the most common cause of TLE [ 18 ]. MTS patients show lower orientation dispersion indices and elevated axial diffusivity in the dentate gyrus on DTI compared to no MTS [ 18 ].…”