RELIABILITY OF VISUAL INSPECTION FOR DETECTION OF VOLUMETRIC HIPPOCAMPAL ASYMMETRY

Volumetric measurement of the hippocampus is of use in localisation of lesions causing focal epilepsy and in lateralisation of epilepsy due to mesial temporal sclerosis. However, it is time consuming and requir es specialised equipment. Hence, we compared volumetric measurement wi th visual detection of hippocampal asymmetry by five trained observers . MRI studies of 19 neurologically normal subjects and of 34 consecuti ve patients with epilepsy and hippocampal volume ratios below the lowe st normal value were employed. Agreement between visual and quantitati ve diagnoses was 59 % for all subjects (kappa = 0.38) and 65 % for tho se with volumetric hippocampal asymmetry, Disagreements in visual and volumetric lateralisation of hippocampal asymmetry were relatively unc ommon. Visual estimates of the extent of hippocampal involvement and t he observers' confidence in the diagnosis influenced the accuracy of v isual inspection. However, discordance in diagnoses occurred even when confidence in the visual diagnosis was high. Reliable visual detectio n occurred for hippocampal volume ratios below 0.7, suggesting that vi sual determination of hippocampal asymmetry is of greatest clinical va lue in the lateralisation of seizure foci in patients already selected for the presence of intractable temporal lobe epilepsy. Volumetric me asurements are particularly important if hippocampal asymmetry is used for seizure localisation in groups of patients with temporal or extra temporal epilepsy.