Megalencephaly and Hemimegalencephaly

Megalencephaly is a developmental disorder characterized by an abnormal increase in the number or size of brain neurons and glia, leading to parenchymal overgrowth. The underlying etiologies allow the classification of megalencephaly into anatomic, related to mutations in signaling pathways governing neuronal growth and migration, and metabolic, caused by abnormal cellular metabolism. Patients can present with abnormal head circumference, mental and psychomotor retardation, seizures, and other features associated with the underlying pathology. Diagnosis relies on neuroimaging and clinical and laboratory assessment, which is improving with progress in the understanding of the molecular underpinnings of this disorder. The prognosis of megalencephaly is determined by the etiology and the extent of neurological involvement. Management includes using the antiepileptic drug carbamazepine, known for its neuroprotective role, mTOR inhibitors, and surgery as a final resort.