Hippocampal volume and T2 relaxation times were determined in an MRI study of 14 children with prolonged febrile convulsions (PFC) who were investigated, 1) within 5 days of a PFC, and 2) at follow-up 4-8 months after the acute study, at the Institute of Child Health, University College, and Great Ormond Street Hospital, London, UK. The initial study previously published (Scott et al, 2002) showed that children examined by MRI within 48 h of a PFC had large hippocampal volumes and prolongation of T2 relaxation times, whereas those with MRI delayed >48 h but within 5 days of PFC had large hippocampal volumes and normal T2 relaxation time. The data were suggestive of hippocampal edema that is resolving within 5 days of a PFC.

Of 14 patients examined at 4-8 month follow-up, 4 had suffered further seizures: 2 had short FC, 1 had PFC and 1 had non-febrile seizures. Repeat MRI showed a significant reduction in hippocampal volume and T2 relaxation time compared to the first exam, and volumes were not different from a control population. In addition, hippocampal volume asymmetry was significantly increased at follow-up compared to initial data, findings consistent with injury and neuronal loss associated with PC. It is postulated that some selectively vulnerable patients may develop mesial temporal sclerosis after a lag period of several years following the PFC or alternatively, the hippocampal asymmetry may represent a post-acute edema return to a pre-existing hippocampal abnormality that antedates the PFC. [1]

COMMENT. In patients with intractable complex partial seizures, those with mesial temporal sclerosis (MTS) had a history of PFC in 33% whereas those without MTS had PFC in only 7% (Falconer, MA, 1972, 1976; see Nelson and Ellenberg, 1981). A causative association between prolonged or complex FC and hippocampal injury and MTS is suggested by clinical and animal studies, but a pre-existing subtle hippocampal maldevelopment is possible in some cases of complex partial epilepsy.

Magnetic brain source imaging (MSI) of focal epileptic activity is reported in 455 cases of epilepsy examined preoperatively at University of Erlangen-Nuernberg, Germany [2]. The average sensitivity of magnetoencephalography (MEG) for specific epileptic activity was 70%, whereas MSI identified the lobe to be resected in 89% of 131 patients who underwent surgery. Those with extratemporal epilepsies were identified in a higher percentage than temporal lobe cases. In a study of 20 patients with idiopathic generalized epilepsy compared to healthy controls, magnetic resonance spectroscopic imaging showed a progressive thalamic neuronal dysfunction, independent of the amount of spike and wave activity [3]. The complementary use of MEG and EEG was useful in localizing the origin of cortical myoclonus in the right temporo-occipital cortex in a 15 year-old girl with Lafora-body disease. [4]