Definition of Megalencephaly

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Megalencephaly: Also called macrencephaly, 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 gender of the child. Head enlargement may be evident at birth or the head may become abnormally large in the early years of life.

Megalencephaly is thought to be related to a disturbance in the regulation of cell reproduction or proliferation. In normal development, neuron proliferation -- the process in which nerve cells divide to form new generations of cells -- is regulated so that the correct number of cells is formed in the proper place at the appropriate time.

Children with megalencephaly may have 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.