Get Informed

Megalencephaly

Megalencephaly

What is Megalencephaly?

Megalencephaly (MEG), also called macrencephaly, is a condition in which an infant or child has 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.

Classification and known presentations

There are 13 types of megalencephaly:

MEG with normal cortex (or presumably normal cortex)

MEG with PNH—plus other anomalies

Clinically defined with AD or unknown inheritance

MEG with PMG and other cortical dysgenesis

Characteristics

Megalencephaly affects males more often than females. Unilateral megalencephaly or hemimegalencephaly is a rare condition that is characterized by the enlargement of one side of the brain. Megalencephaly is different from macrocephaly (also called megacephaly or megalocephaly), which describes a big head, and which doesn’t necessarily indicate abnormality. Large head size is passed down through the generations in some families.

Symptoms

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

Causes

Megalencephaly is thought to be related to a disturbance in the regulation of cell production in the brain. 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 produced in the proper place at the appropriate time. In a megalencephalic brain, too many cells are produced either during development or progressively as part of another disorder, such as one of the neurofibromatoses or leukodystrophies.

Diagnosis

The evaluation of a patient with suspected megalencephaly will usually consist of questions about medical history and family history, a physical exam that includes head measurements, and a developmental and/or neurological exam.

Treatment

There is no standard treatment for megalencephaly. Treatment will depend upon the disorder with which the megalencephaly is associated and will address individual symptoms and disabilities.

Prognosis

The prognosis for infants and children with megalencephaly depends upon the underlying cause and the associated neurological disorders. The prognosis for children with hemimegalencephaly is poor.

Prevalence

Megalencephaly is a very rare disorder, though the exact prevalence is unknown.

Sources

  1. Barkovich AJ, Guerrini R, Kuzniecky RI, Jackson GD, Dobyns WB. “A developmental and genetic classification for malformations of cortical development:  update 2012. Brain 2012. 10.1093/brain/aws019.
  2. Mirzaa G, Dodge NN, Glass I, Day C, Gripp K, Nicholson L, et al. Megalencephaly and perisylvian polymicrogyria with postaxial polydactyly and hydrocephalus: a rare brain malformation syndrome associated with mental retardation and seizures. Neuropediatrics 2004;35:353-9.