Progressive hemispheric shrinking in hemimegalencephaly: a possible role for seizure-related neuronal loss

Hemimegalencephaly (HME) is a developmental brain lesion consisting of a unilateral enlarged, dysplastic, and often highly epileptogenic cerebral hemisphere. Most patients exhibit early onset intractable seizures, status epilepticus, hemiplegia, hemianopsia, and developmental delay. Major surgical procedures are advocated for limiting the devastating consequences of epilepsy. We studied a female with HME, early onset intractable seizures and recurrent status epilepticus, in whom progressive hemiatrophy of the enlarged hemisphere and normal growth of the contralateral hemisphere, exceeding the size of the dysplastic hemisphere, was demonstrated by magnetic resonance imaging. Histopathology, following functional hemispherectomy at the age of 7 years, demonstrated severe neuronal loss with an elevated number of cells exhibiting the morphological and biochemical features of apoptosis. Eighteen months after surgery the patient was seizure-free (Engel class I) and exhibited improved motor and language skills, alertness and social behaviour. We hypothesize that nearly continuous seizure activity might sustain seizure-induced brain injury in the dysplastic hemisphere but causal heterogeneity and associated anatomical factors may influence differently the individual predisposition to atrophic changes.