Hemimegalencephaly and Epilepsy: An Overview

Introduction: Cerebral cortical development is a highly complex process influenced by environmental, genetic and functional abnormalities. Hemimegalencephaly (HME) is a rare brain malformation that involves overgrowth of one hemisphere. Clinically macrocephaly, mental retardation, contralateral hemiparesis, hemianopsia and intractable epilepsy may be present. Diagnosis is mainly done with image and clinical findings. MRI typically reveals an enlarged cerebrum involving at least one lobe, with a thickened cortex; broad gyres; abnormal gray-white matter differentiation with abnormal sign; neuronal heterotopia, ventricle asymmetry, and basal ganglia and internal capsule abnormalities. Electroencephalographic abnormalities usually involve the affected hemisphere, with an asymmetric amplitude of the normal, age-related rhythms; slow, rhythmic or fast activity and multifocal unilateral or bilateral high-amplitude spikes and spike-wave complexes. Histopathologic changes include abnormal gyrification, with loss of cortical lamination, neuronal heterotopia, gliosis, large bizarre neurons and balloon-cells. The presence of highly refractory seizures in patients with HME is an important factor to consider epilepsy surgery in these patients. Methods: Multiple surgical techniques are actually being used for hemispheric disconnection. We discuss here the main surgical techniques that are used for hemispheric disconnection. Conclusions: Postsurgery outcome for HME may be not as good as that for focal lesions with approximately 40% of patients being seizure free, but the main indication for surgery in these patients may be preventing additional cognitive injury and developmental delay. Surgical complications are observed in most of the series of patients with HME submitted to hemispheric surgery. Minimal resections may contribute do diminish surgical complications.