National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Hemimegalencephaly


Other Names:
Macrencephaly; Unilateral Megalencephaly
Categories:
This disease is grouped under:

Hemimegalencephaly is a rare malformation involving one side of the brain.[1][2] It may occur alone or in association with other syndromes such as Proteus syndrome, tuberous sclerosis, linear sebaceous nevus syndrome, neurofibromatosis, Sturge-Weber syndrome, or Klippel-Trenaunay syndrome.[1] Children with this disorder may have a large, asymmetrical head accompanied by seizures, partial paralysis, and impaired cognitive development.[2][3] Because the seizures associated with hemimegalencephaly are difficult to treat with anticonvulsant medications, a surgery called hemispherectomy is often the most successful treatment.[1][3] The cause of hemimegalencephaly is not fully understood, but involves a disturbance of cells early in development and likely involves genes involved in patterning and symmetry.[1][2]

Last updated: 11/27/2015
Because the seizures associated with hemimegalencephaly are difficult to control with anti-epileptic medications, most patients undergo surgery to separate one hemisphere of the brain from the other (hemispherectomy). There are several surgical options to consider. One is functional hemispherectomy which involves severing the nerves and tissue connecting one side of the brain to the other, leaving the brain within the skull. Another is a complete or anatomic hemispherectomy in which the affected side of the brain is surgically removed. These surgeries are usually performed by a neurosurgeon with experience treating epilepsy syndromes.[1][3] Over time, the remaining side of the brain may take over the functions lost.[3] 
Last updated: 11/27/2015

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • The Christopher A. Walsh Laboratory is interested in the development of the cerebral cortex. Abnormal development of the cerebral cortex in humans results in epilepsy, autism, intellectual disability, dyslexia, and other learning disorders, and perhaps some psychiatric conditions as well. Several of their projects are directed at trying to understand the basic biology of the cortex by studying the mutations that disturb its development. Conditions that they are currently researching include: double cortex syndrome, periventricular heterotopia, schizencephaly, perisylvian polymicrogyria and Walker Warburg syndrome. Click on the link above to access further information about this research.

  • Orphanet lists European clinical trials, research studies, and patient registries enrolling people with this condition. 

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • 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 Johns Hopkins Medicine Web site provides information on hemimegalencephaly. Click on the link above to view this information page.
  • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

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.
  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • 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.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know. Submit a new question

  • My granddaughter has hemimegalencephaly and is suffering with seizures that thus far are not being controlled with any medications. We have been told the next step is to have brain surgery. Can you provide me with information about this? See answer

  • My grandson was recently diagnosed with hemimegalencephaly. He's currently on-track developmentally. Are there degrees of severity with this condition? Where can we find the best information or an expert we could talk to? See answer


  1. Crino P. Hemimegalencephaly. National Organization for Rare Disorders (NORD). 2012; http://rarediseases.org/rare-diseases/hemimegalencephaly/. Accessed 11/27/2015.
  2. NINDS Megalencephaly Information Page. National Institute of Neurological Disorders and Stroke (NINDS). June 30, 2015; http://www.ninds.nih.gov/disorders/megalencephaly/megalencephaly.htm. Accessed 11/27/2015.
  3. Hemimegalencephaly. Johns Hopkins Medicine. http://www.hopkinsmedicine.org/neurology_neurosurgery/centers_clinics/epilepsy/seizures/causes/hemimegalencephaly.html. Accessed 11/27/2015.