Coronal high resolution T2 and FLAIR are best to diagnose MTS.
Findings include reduced hippocampal volume that is hippocampal atrophy, increased T2 signal, abnormal morphology that is loss of internal architecture and interdigitations of hippocampus.
Although comparing with opposite is easiest, it must be remembered that up to 10% of cases are bilateral, and thus if symmetry is the only feature being evaluated, many cases may be misinterpreted as normal.
Often mentioned, but probably one of the least specific findings, is enlargement of the temporal horn of the lateral ventricle. If anything, care must be taken to not allow an enlarged horn to trick you to over diagnosis as hippocampal atrophy.