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Genetic and Rare Diseases Information Center (GARD)

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Other Names for this Disease
  • Macrencephaly
  • Unilateral Megalencephaly
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Hemimegalencephaly is a rare malformation involving one side of the brain. It may occur alone or in association with epidermal nevus syndrome, Proteus syndrome, or Klippel-Trenaunay syndrome. It usually causes partial epilepsy, which may be treated with hemispherectomy. Hemimegalencephaly can also cause intellectual disability and impair normal movement on the side of the body opposite of the malformation. Symptoms range from mild to severe. The cause of this condition is not fully understood, but involves a disturbance of cells early in development and likely involves genes involved in patterning and symmetry.[1]

Last updated: 5/6/2010


  1. Sarnat HB, Flores-Sarnat L. Developmental disorders of the nervous system. In: Bradley WG et al. Neurology in Clinical Practice, 5th ed. Philadelphia, PA: Butterworth-Heinemann; 2008;
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Basic Information

  • MedlinePlus provides more information on head and brain malformations. MedlinePlus is a Web site designed by the National Library of Medicine to help you research your health questions.
  • The Merck Manuals Online Medical Library has an information page on brain anomalies in general. Click on the link above to view the information page.
  • The Johns Hopkins Medicine Web site provides information on hemimegalencephaly. Click on the link above to view this information page.
  • Information on cephalic disorders and megalencephaly can be found on the National Institute of Neurological Disorders and Stroke (NINDS) Web site. To view the information pages click on the links above.
  • The National Organization for Rare Disorders (NORD) is a federation of more than 130 nonprofit voluntary health organizations serving people with rare disorders. Click on the link to view information on this topic.

In Depth Information

  • MeSH® (Medical Subject Headings) is a terminology tool used by the National Library of Medicine. Click on the link to view information on this topic.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Hemimegalencephaly. Click on the link to view a sample search on this topic.