Abstracts

Rationale: PFS, the most common cause of childhood convulsive status epilepticus (CSE), is hypothesised to lead to epilepsy. Recent reports of HIMAL in patients with epilepsy and in children with PFS suggest that HIMAL increases susceptibility of the brain to PFS and thus, HIMAL may be more common in PFS compared to the general population. From an ongoing 10-year population-based follow-up cohort study on the outcomes of convulsive status epilepticus, in which children are having detailed neuroimaging and neurological assessments, we report on the prevalence of HIMAL on brain MRI in children with PFS compared to controls.Methods: Brain MRI was performed on a Siemens 1.5T scanner. In addition to conventional sequences, T1-weighted images were acquired using a three-dimensional fast low angle shot (3D FLASH) sequence providing 1mm slices for detailed anatomical definition. Scans of 25 children with PFS and 25 randomly selected age-matched controls were analysed in detail by a trained paediatric neuroradiologist blinded to clinical details. HIMAL was defined as incomplete rotation of the hippocampus with normal size and signal intensity, but abnormally rounded shape and blurred internal architecture (Shinnar et al. Neurology 2012;29:871-77). Other features of HIMAL such as vertical orientation of collateral sulcus angle, abnormal size and position of fornix and configuration of temporal horn of the lateral ventricle were examined. Temporal lobe and extra-temporal abnormalities were also recorded. Prevalence of HIMAL in the two groups was compared using Fisher s exact test in SPSS v21.Results: The demographics of children with PFS (mean age 9.96y, 12 male) and controls (mean age 10.6y, 12 male) were similar. Mean interval between CSE and MRI in the PFS group was 8.15 (range 6.7 to 9.6) years. 2 children who had PFS (8%, 95%CI 2.2-25.0) and 3 controls (12%, 95%CI 4.2-30.0) fulfilled full criteria for HIMAL (p=1.0). HIMAL was observed on the left side in both PFS children. In controls, HIMAL was bilateral in 2 and on the right side in 1. Only the body of the hippocampus was affected in all. The angle of the collateral sulcus on the affected side was >45 in all. The position of the fornix was low in 2 and enlarged temporal horn was seen in 1. Fornix, temporal lobe and corpus callosum sizes were normal in all. All 5 were neurologically normal; neither of the 2 who had PFS experienced subsequent afebrile seizures. In addition, 2 other controls and 1 with PFS had features of HIMAL except blurring of the internal architecture. Isolated unilateral low position of fornix was seen in 8 (32%, 95%CI 17-52%) PFS children and 10 controls (40%, 95%CI 23-59%). 2 children in each group (8%, 95%CI 2.2-25.0) had unilateral enlargement of temporal horn.Conclusions: HIMAL is not uncommon in the general population. In our unique CSE cohort, whether full or partial diagnostic criteria for HIMAL are used, the prevalence of HIMAL is not higher in PFS children compared to controls.