Mossy fiber sprouting in pilocarpine-induced status epilepticus rat hippocampus: a correlative study of diffusion spectrum imaging and histology.

Mossy fiber sprouting (MFS) is the main characteristic of temporal lobe epilepsy (TLE), which is highly correlated with the frequencies of recurrent seizures as well as degrees of severity of TLE. A recent MRI technique, referred to as diffusion spectrum imaging (DSI), can resolve crossing fibers and investigate the intravoxel heterogeneity of water molecular diffusion. Being able to achieve higher accuracy in depicting the complex fiber architecture, DSI may help improve localization of the seizure-induced epileptic foci. In this study, two indices of DSI, which represented the mean diffusivity (MSL) and diffusion anisotropy (DA), were proposed. A correlative study between diffusion characteristics and the severity of MFS was investigated in the pilocarpine-induced status epilepticus (SE) rat model. Nine SE rats and five control rats were studied with MRI and histological Timm's staining. For MSL, no significant correlation was found in the dentate gyrus (DG), r=-0.36; p=0.2017, and positive correlation was found in cornu ammonis (CA3), r=0.62; p=0.0174. The correlation between DA and Timm's score showed positive correlation in DG, r=0.71; p=0.0047, and negative correlation in CA3, r=-0.63; p=0.0151. Our results were compatible with the previous reports on fiber architecture alterations in DG and CA3 subregions. In conclusion, the histological correspondence of DSI indices was demonstrated. With DSI indices, longitudinal follow-up of hippocampal fiber architecture can be achieved to elucidate the pathophysiology of TLE, which might be helpful in disease localization.