Limited utility of interictal apparent diffusion coefficient in the evaluation of hippocampal sclerosis

Quantitative measurement of diffusion has been studied as an independent parameter for the identification and characterization of abnormal hippocampi and temporal lobes in epileptic patients.

In order to study the diagnostic value of magnetic resonance diffusion weighted imaging (DWI) and the apparent diffusion coefficient (ADC) from the temporal region, interictal DWI and ADC values were prospectively obtained from both hippocampal areas and temporal lobes bilaterally and compared between 19 normal volunteers and 20 medial temporal lobe epilepsy (MTLE) patients.

In all patients, visual assessment of DWI failed to lateralize the lesion. However, the overall correct lateralization rate of interictal ADC was 100% (20/20) if the side with the higher ADC value was considered to be abnormal. Comparison of the MTLE lesion side values with those of the normal volunteers revealed that the ADC values measured from the hippocampal areas and temporal lobes of the MTLE patients were significantly higher than those from the normal volunteers on the lesion side (P < 0.05) and also on the contralateral side although not statistically significant. The absolute differences between the ADC values of the higher and lower side, in both the hippocampus and the temporal lobe, were not significant among the normal volunteers and the MTLE patients.

Although the correct lateralization rate of interictal ADC in the MTLE patients was 100%, the application of elevated ADC value as a diagnostic criteria for MTLE was disappointing because such elevation in ADC values was not limited only to the ipsilateral temporal region but also in the contralateral side in MTLE.