Megalencephaly (or macrencephaly) is a condition in which the brain is abnormally large.

Unilateral megalencephaly or hemimegalencephaly is a rare condition characterized by the enlargement of one-half of the brain.

Symptoms of megalencephaly may include delayed development, convulsive disorders, corticospinal (brain cortex and spinal cord) dysfunction, and seizures.

Unilateral Megalencephaly Macrencephaly None Hemimegalencephaly is a rare neurological condition in which one-half of the brain, or one side of the brain, is abnormally larger than the other.

Mutations in the LYK5/STRADα gene are associated with polyhydramnios, megalencephaly and symptomatic epilepsy (collectively known as the PMSE syndrome).