National Organization for Rare Disorders, Inc.
It is possible that the main title of the report Hemimegalencephaly is not the name you expected.
Hemimegalencephaly (HME) is a rare neurological condition in which one-half of the brain, or one side of the brain, is abnormally larger than the other. The structure of the brain on the affected side may be markedly abnormal or show only subtle changes. In either case, as a consequence of this size and structural differences, the enlarged brain tissue causes frequent seizures, often associated with cognitive or behavioral disabilities. Seizures in association with HME often begin in early infant life including an association with infantile spasms. Hemimegalencephaly may occur as an isolated or sporadic brain malformation or it may be associated with other neurodevelopmental syndromes. Thus, when detected, HME should prompt a search for other syndromic diagnoses.
Anti-seizure medications typically are not effective in controlling seizures in HME and thus, surgery is often recommended to control the seizures. If the affected side is surgically removed (anatomic hemispherectomy) or disconnected from the other brain structures (functional hemispherectomy), the remaining side of the brain may gradually take over the functions normally performed by the affected side.
Any combination of altered mental status, seizures, enlarged head, and /or altered skin pigmentation should prompt consideration of HME. In general, the presence of HME is definitively diagnosed by brain MRI. With the evolution of more widespread fetal imaging including ultrasound and MRI, a number of HME cases are detected prenatally.
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This is an abstract of a report from the National Organization for Rare Disorders (NORD). For a full-text version of this report, go to www.rarediseases.org and click on Rare Disease Database under "Rare Disease Information".
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Last Updated: 2/24/2012
Copyright 2012 National Organization for Rare Disorders, Inc.
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