Hemimegalencephaly: prenatal diagnosis and outcome

Hemimegalencephaly (HME) is a developmental abnormality of the central nervous system (CNS) which may present as either a syndromic or isolated case. Here, we present two cases of early prenatal diagnosis of HME. Prenatal CNS ultrasound and MRI in the first case revealed ventricular asymmetry, midline shift with displacement of the occipital lobe across the midline, large dilatation mainly at the posterior horn of the left lateral ventricle, and a head circumference in the 90th percentile without involvement of the brain stem and cerebellum, as well as abdominal lymphangioma. Right hemispherectomy was performed at 3 months of age due to intractable seizures. The pathological specimen showed findings characteristic of HME, including a disorganized cytoarchitecture with lack of neuronal lamination, focal areas of polymicrogyria, and neuronal heterotopias with dysplastic cells. In the second case, 2D and 3D neurosonography demonstrated similar findings (asymmetry of cerebral hemispheres, midline shift, and dilation of the posterior horn of the left lateral cerebral ventricle). Posterior fossa structures were unremarkable. HME was diagnosed and the pregnancy was terminated. Autopsy findings confirmed the diagnosis of HME.