BILATERAL HIPPOCAMPAL VOLUME LOSS IN PATIENTS WITH A HISTORY OF ENCEPHALITIS OR MENINGITIS

Volumetric analysis of high-quality magnetic resonance imaging (MRI) s cans identifies asymmetric hippocampal atrophy in most patients with t emporal lobe epilepsy. However, bilateral hippocampal atrophy can be m issed by unnormalized volume measures. We considered two patient group s with temporal lobe epilepsy, one with a history of febrile convulsio ns (FC, n = 14) and one with a history of encephalitis or meningitis ( E/M, n = 12), to compare the prevalence of bilateral volume loss betwe en the groups. A volume normalization process defines a normal range o f hippocampal volumes in control subjects (n = 32). Normalized volumes indicated that 11 of 14 subjects with a history of FC had unilateral hippocampal atrophy and 9 of 12 subjects with a history of E/M had bil ateral hippocampal atrophy as compared with the controls. Visual asses sments of unilateral hippocampal atrophy(n = 17) correlated well with measured unilateral volume loss (n = 14), but visual assessment of bil ateral hippocampal atrophy (n = 3) correlated poorly with measured bil ateral volume loss (n = 12). Mean age at seizure onset was lower in th e FC group (7 years) than in the E/M group (13 years), but other clini cal features were similar between the two groups. Hippocampal volume n ormalization is necessary to detect bilateral volume loss, which is co mmon in patients with a history of encephalitis or meningitis.