Abstracts

Rationale: There is an association between temporal lobe epilepsy due to mesial temporal sclerosis (MTS) and a childhood history of convulsive status epilepticus (CSE), in particular prolonged febrile seizures (PFS). Imaging done within 72 hours of PFS has shown increased hippocampal volumes and T2 signal, and follow-up imaging at 4 months has shown an increase in hippocampal asymmetry. These changes have been interpreted as suggestive of hippocampal injury caused by the PFS. As part of an ongoing longitudinal prospective study of childhood CSE we have conducted hippocampal volume measurements to characterise the time course of any changes. Methods: Children are being enrolled from London hospitals following an episode of CSE and their clinical and demographic data collected. Enrolled patients underwent MRI investigations in a Seimens Avanto 1.5T scanner under sedation a mean of 21 days (range 9 - 64) after their episode of CSE. The investigations included a T1 weighted three-dimensional fast low angle shot (3D FLASH) which was used to derive the hippocampal volumes. Hippocampal volumes were measured by manually tracing consecutive coronal slices with simultaneous reference to a 3 dimensional visualisation in 3 orthogonal planes using a T1 weighted FLASH sequence dataset. An asymmetry index for each patient was calculated by dividing the difference in volume between left and right hippocampi by mean volume. Data was analysed in SPSS 14.0 (Chicago, Illinois) for Windows using independent samples t-test and Moses extreme reactions testing to test for differences in demographic composition and hippocampal asymmetry index between children with PFS and children with CSE from other causes. Results: To date 20 patients (10 male) have been enrolled. Mean age was 2.81 years (range 0.21 - 15.5). Twelve had a PFS and 8 had CFS due to other aetiologies. The two groups did not differ significantly in age, sex, or time to first scan. Hippocampal volume was correlated with intracranial volume (r = 0.93. p < 0.001) and with age (r = 0.546, p < 0.001) across all time points. Patients with PFS had a more extreme hippocampal asymmetry index than those with other types of CSE at baseline (0.052, p = 0.054, Moses extreme reaction test). Follow-up studies at 4 and 8-12 months after the initial episode of CSE to characterise the progression of this asymmetry are underway. Conclusions: PFS is associated with more extreme hippocampal asymmetry within an average of 3 weeks of the event supporting the view that PFS is more likely to be associated with hippocampal injury leading to MTS than other types of CSE.