Abstracts

To document the clinical, neurophysiological and neuroradiological spectrum of hemimegalencephaly.
Children presenting to Great Ormond Street Hospital with hemimegalencephaly were identified from epilepsy surgery, radiology and neurophysiology databases. A case note review was performed to ascertain clinical details including epilepsy history, neurological deficit, IQ, impact of epilepsy surgery if performed and syndromic diagnosis. Neuroimaging and EEGs, including video telemetry, were analysed and abnormalities categorised.
41 children (16 female; 25 male) were identified with hemimegalencephaly. 17 (41%) had right hemimegalencephaly, 21 (51%) left and 2 had bilateral. 40/41 had epilepsy with a mean age of seizure onset of 0.42 years (range day 1 [ndash] 6.5 years; median 0.06 years). Neonatal seizures occurred in 23 (56%) and convulsive status epilepticus had occurred in 6 (15%). The commonest seizure type was complex partial seizure (78%), though many seizure types occurred (myoclonic, atonic, clonic, tonic, infantile spasms and focal motor). Infantile spasms had occurred in 43%. 3 children had no hemiplegia. The child without epilepsy had normal cognition, 3 (8%)children had mild learning difficulties (2 with seizure onset after the age of 5 years) and the rest had moderate or severe learning difficulties. 17/41 (41%) had a syndrome diagnosis (Proteus, Linear Sebaceous Naevus, Klippel-Trenaunay-Weber, Curry-Jones and Oro-facial-digital). 26/41(63%) underwent 31 epilepsy surgery procedures at the mean age of 3.6 years (range 0.16 [ndash] 18.16 years). Post-operative followup (mean time of 4.76 years post-operatively) revealed an Engel III or better outcome with 10 (38%) seizure free; all had made developmental progress. There were varying degrees of MRI abnormality that generally did not correlate consistently with clinical features. However the child with normal cognition who did not have epilepsy had a normal appearance of cerebral cortex on MRI though had other radiological findings fulfilling criteria for hemimegalencephaly. Major EEG findings were burst suppression, triphasic complexes and an anterior alpha-like pattern and there was a suggestion that these changes are age dependant. There was no clear correlation between contra-lateral hemisphere epileptic discharges and outcome from epilepsy surgery.
There is heterogeneity in the clinical, neuroradiological and neurophysiological features within the spectrum of hemimegalencephaly. The majority of children have significant learning disability, intractable epilepsy and hemiplegia though with no clear cerebral cortical abnormality on neuro-imaging normal cognitive skills and absence of epilepsy can occur. Hemispherectomy is a beneficial treatment for children with hemimegalencephaly both in terms of seizure control and development.