HIPPOCAMPAL VOLUMETRICS DIFFERENTIATE PATIENTS WITH TEMPORAL-LOBE EPILEPSY AND EXTRATEMPORAL LOBE EPILEPSY

Objective: To determine whether the occurrence of hippocampal formatio n (HF) volumetric asymmetry can reliably discriminate between complex partial seizures (CPSs) of a temporal lobe origin and CPSs of an extra temporal lobe origin in a prospective study of patients with intractab le CPSs (approximately 70% of patients have electrographic foci in the temporal lobe [HF volumetric asymmetry on magnetic resonance imaging scans has been shown to lateralize such foci reliably]). Design: We ex amined HF volumetrics on magnetic resonance imaging scans that were ac quired with a 1-T magnetic resonance imaging scanner (Siemens Magnetom , Siemens Medical Systems, Iselin, NJ) by using magnetization-prepared rapid gradient echo three-dimensional sequences (producing a gapless series of high-contrast 1.25-mm images). These data were compared with ictal, interictal, invasive, and noninvasive videoelectroencephalogra phic monitoring data, functional imaging data, and outcome data to def ine each patient's type of epilepsy. Setting and Patients: Forty-one p atients were recruited from a tertiary university comprehensive epilep sy program, and 22 control subjects were recruited from the neurologic ally normal university community. Results: Among the control subjects, the difference in HF volumetrics (right-left HF volumetrics) was +0.0 85+/-0.253 cm(3). Of the 41 patients, 25 had temporal lobe epilepsy. W hen we set the upper limit of normal at the mean+/-3 SDs, all patients beyond the upper limit had CPSs of a temporal lobe origin. Of the pat ients with temporal lobe epilepsy, only three fell within normal limit s. No patient with CPSs of an extratemporal lobe origin fell beyond th e upper limit. Conclusion: The presence of significant HF volumetric a symmetry makes it highly unlikely that a patient's CPSs are of an extr atemporal lobe origin.