Value of magnetic resonance imaging-based measurements of hippocampal formations in patients with partial epilepsy.

OBJECTIVE

To determine the occurrence of magnetic resonance imaging-detected hippocampal atrophy (HA) in patients with partial epilepsy (temporal and extratemporal, cryptogenic, or symptomatic). Magnetic resonance imaging-detected HA has been demonstrated to be both sensitive and specific for hippocampal sclerosis in cryptogenic temporal lobe epilepsy.

DESIGN

Patients' hippocampal formations were measured on a computerized system using T1-weighted, 5-mm contiguous magnetic resonance coronal images made perpendicular to the hippocampus long axis. Hippocampal atrophy was defined on the basis of a normative asymmetry index and correlated with the epileptogenic focus defined by clinical, electroencephalographic, and magnetic resonance imaging (apart from HA) localizing data.

PATIENTS AND CONTROL SUBJECTS

Seventy patients with intractable complex partial seizures of temporal, extratemporal, or undefined origin and 21 healthy control subjects.

RESULTS

Hippocampal atrophy was present in 70% of patients with cryptogenic temporal lobe epilepsy (TLE) (n = 40), 44% of patients with symptomatic TLE (n = 9), 29% of patients with extratemporal epilepsy (n = 14), and 6% of unclassified patients (n = 16). In the cryptogenic TLE category, HA was marked and usually concordant (93%) with electroencephalographic lateralization. Hippocampal atrophy was often mild in the extratemporal epilepsy category. With the use of a wider confidence interval (+/- 3.1 SD instead of +/- 2.2 SD), HA specificity for TLE increased to 93%, HA specificity for lateralizing cryptogenic TLE reached 96%, and HA sensitivity for cryptogenic TLE stood almost unchanged (68%). We found a link between early convulsions and HA occurrence.

CONCLUSIONS

Hippocampal atrophy is a marker for TLE. Dual pathologic findings are detected in 44% of symptomatic TLE cases. Mild HA is rarely associated with extratemporal epilepsy. Magnetic resonance imaging-based hippocampal volumetric analysis is a useful method to localize the origin of partial complex seizures.