Mesial temporal sclerosis (MTS), also commonly referred to as hippocampal sclerosis, is the most common association with intractable temporal lobe epilepsy (TLE), seen in up to 65% of autospy studies (significantly less on imaging). There is controversy as to which is causative: is MTS the result of, or the cause of TLE? The dentate gyrus and the CA1, CA3, and CA4 sections of the hippocampus are primarily involved, with cell loss and gliosis seen histologically.
On MRI it is recognized by:
– reduced hippocampal volume
– increased signal on T2WI
– abnormal morphology
Other causes of temporal lobe epilepsy (TLE) should be considered, especially as small temproal lobe cortical tumours can have similar appearances.
Read more about MTS at Radiopaedia.org here.
University of Rochester medical center 
Credit: Dr Frank Gaillard