Abstracts

Objective: From this work, participants should appreciate the extent to which hippocampal damage can result from remote seizure activity.
Hippocampal T2 (HT2) relaxometry has been shown to be useful in pre-surgical assessment of adults with MTS, and is correlated with side of seizure onset and histological severity. A long period of active epilepsy has been negatively correlated with hippocampal volume, generating the hypothesis that ongoing epilepsy causes damage to the hippocampus, possibly including those that are not the primary epileptogenic focus. Histological data suggests that the latter hippocampal abnormalities are subtle. The aim of this study is to examine hippocampi in children with partial epilepsy using HT2 relaxometry, with the aim of comparing the findings from patients in whom the hippocampus is the primary seizure focus with those from patients with seizures arising from elsewhere. This may provide insight into the cause of hippocampal abnormalities in children with active partial epilepsy.
METHODS: 95 consecutive children with partial epilepsy and 22 age-matched controls underwent MR imaging, including HT2 relaxometry using a modified CPMG sequence. Visual analysis of structural scans was carried out to identify lesions associated with partial epilepsy. Abnormal quantitative HT2 was defined as greater than 2SD from the control mean after adjustment for age. Right to left asymmetry was investigated by comparing ratios of higher to lower HT2 using a Mann-Whitney U test. Group abnormalities were investigated with multiple linear regression
RESULTS: HT2 was dependant upon age in the age range investigated (33-233 months, p=0.001). Patients were divided, on the basis of clinical, EEG and visual MRI assessment, into 3 groups; those with TLE and MTS (MTS-TLE), lesional TLE (l-TLE) or extratemporal epilepsy (ETE). Patients with MTS-TLE had asymmetry of HT2 (p[lt]0.001). 29/35 (84%) had abnormal HT2 and in 9% the abnormality was bilateral. On group analysis, HT2 in the sclerotic hippocampus was prolonged by a mean of 19 ms (95% CI = 15-22 ms; p[lt]0.001). In the non-sclerotic hippocampus HT2 was prolonged by a mean of 3.4 ms (95%CI, 1-6ms; p=0.01) when compared with controls. 10/32 (32%) patients with l-TLE and 9/29 (23%) of those with ETE had an abnormal HT2 in at least one hippocampus. On group analysis, patients with l-TLE had prolongation of HT2 by a mean of 4.4 ms (95% CI, 2-7ms; p=0.001) and those with ETE had prolongation of HT2 by a mean of 3.8 ms (95% CI, 1-7 ms; p=0.006) when compared with controls, after adjustment for age.
CONCLUSIONS: As in adults, HT2 is shown to be useful in the pre-surgical assessment of children with MTS. In addition, the extent of prolongation of HT2 in hippocampi that are not primary epileptogenic foci was found to be similar in all 3 patient groups studied. The wide variety of structural associations and varied sites of epileptogenic foci suggest that the abnormalities are likely to be caused by ongoing seizure activity rather than by underlying aetiology or site of epileptogenic focus.
[Supported by: The Wellcome Trust]