Quantitative MRI of mesial temporal structures in temporal lobe epilepsy

Hippocampal sclerosis (HS) is the most common pathology associated with intractable temporal lobe epilepsy (TLE). MRT features of HS include hippocampal atrophy and an increased T2 signal. Hippocampal volume loss can be quantified using MR-based hippocampal volume measurement, and the hippocampal T2 relaxation time can be measured on a hippocampal T2 map. Visual assessment of high quality T2- and thin sliced IR T1-weighted images along the axes of the hippocampus allows reliable detection of unilateral diffuse HS, the most common variant of KS. A combination of quantitative hippocampal MRI techniques may be required to detect some variants of HS, such as bilateral HS, and to better define the range of normality. Examples of unusual findings are presented and clinical correlations are discussed. The combination of AT2 mapping and FLAIR is a sensitive method with which to detect small lesions which are not seen on standard MR images in the amygdalae of patients with intractable TLE. These MRI techniques will detect an abnormality in mesial temporal structures in similar to 80% of patients with intractable TLE not associated with a foreign tissue lesion.