Health Dictionary
Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.
Hemimegalencephaly
Introduction
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Overview
Overview
Megalencephaly is a type of cephalic disorder. Also called macrencephaly, this is a condition in which there is an abnormally large, heavy, and usually malfunctioning brain. By definition, the brain weight is greater than average for the age and sex of the infant or child. Head enlargement may be evident at birth or the head may become abnormally large in the early years of life.
Symptoms of megalencephaly may include delayed development, convulsive disorders, corticospinal (brain cortex and spinal cord) dysfunction, and seizures. Megalencephaly affects males more often than females.
The prognosis for individuals with megalencephaly largely depends on the underlying cause and the associated neurological disorders. Treatment is symptomatic. Megalencephaly may lead to a condition called macrocephaly. Unilateral megalencephaly or hemimegalencephaly is a rare condition characterized by the enlargement of one-half of the brain. Children with this disorder may have a large, sometimes asymmetrical head. Often they suffer from intractable seizures and mental retardation. The prognosis for those with hemimegalencephaly is poor.
The prognosis for hemimegalencephaly ranges from poor to highly functioning. In some cases, children with hemimegalencephaly are severely mentally retarded and must undergo a hemispherectomy to stop seizure activity. In others, seizure activity can be controlled by medication; and the affected child develops mentally and physically trailing normal development by 1-2 years.