Internal Structural Changes in the Hippocampus Observed on 3-Tesla MRI in Patients with Mesial Temporal Lobe Epilepsy

Objective Hippocampal sclerosis (HS) is observed in many intractable, mesial temporal lobe epilepsy (MTLE) patients. We aimed to delineate the internal structural changes (ISC) shown as loss of internal architecture in the hippocampus on 3-Tesla magnetic resonance imaging (3T-MRI) due to its higher spatial resolution. Methods We studied 12 MTLE patients who exhibited unilateral HS on conventional 1.5 Tesla-MRI. Using 3T-MRI, high resolution T2-weighted coronal images of the hippocampus were investigated by visual inspection without the use of detailed clinical information. In addition, tissue samples obtained from four patients who underwent epilepsy surgery were analyzed histopathologically. Results In addition to hippocampal atrophy (HA) in the abnormal side, blurring of the low-intensity streak, i.e., ISC, in the hippocampus was seen in 12 patients and atrophy or high signal intensity was observed in Ammon's horn or the dentate gyrus in nine patients. After four patients underwent epilepsy surgery, tissue samples showed astrogliosis and a loss of pyramidal neurons in the hippocampal body, concordant with ISC or HA on MRI examination. Conclusion High-resolution MRI suggests that minute internal structural changes in the hippocampus reflect neuronal cell loss or gliosis, possibly in the early stage, and also show laterality of changes more sensitively. Different internal structural changes could further subclassify HS and may predict the surgical outcomes of seizure control based on the clinicopathological correlation.