Detection of hippocampal pathology in intractable partial epilepsy

Abnormal T2-weighted signal intensity in the hippocampus may be difficult to detect visually, and T2 mapping provides an objective means of assessing signal abnormality. We investigated 50 adult outpatients suffering from intractable partial epilepsy with MRI optimized to detect hippocampal and cortical gray matter abnormalities, and with MR T2 relaxation mapping. The range of normal hippocampal T2 relaxation times is small (99 to 106 msec), and the measurements are reproducible between observers. There were abnormal hippocampal T2 relaxation times in the hippocampus ipsilateral to the site of seizure origin in 70% of patients studied, with the more severe abnormality in the ipsilateral hippocampus in all cases. All hippocampal T2 measurements greater than 116 msec were associated with temporal lobe epilepsy and pathologic or MRI evidence of hippocampal sclerosis, or both. Bilateral abnormalities were present in 29% of cases with hippocampal sclerosis.