You are reading a NORD Rare Disease Report Abstract. NORD’s full collection of reports on over 1200 rare diseases is available to subscribers (click here for details). We are now also offering two full rare disease reports per day to visitors on our Web site.
NORD is grateful to Peter Crino, MD, PhD, Director of the PENN Epilepsy Center and Associate Professor of Neurology, Perelman School of Medicine, University of Pennsylvania, for assistance in the preparation of this report.
Synonyms of Hemimegalencephaly
- unilateral megalencephaly
- No subdivisions found.
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.
The information in NORD’s Rare Disease Database is for educational purposes only. It should never be used for diagnostic or treatment purposes. If you have questions regarding a medical condition, always seek the advice of your physician or other qualified health professional. NORD’s reports provide a brief overview of rare diseases. For more specific information, we encourage you to contact your personal physician or the agencies listed as “Resources” on this report.
The National Organization for Rare Disorders (NORD) web site, its databases, and the contents thereof are copyrighted by NORD. No part of the NORD web site, databases, or the contents may be copied in any way, including but not limited to the following: electronically downloading, storing in a retrieval system, or redistributing for any commercial purposes without the express written permission of NORD. Permission is hereby granted to print one hard copy of the information on an individual disease for your personal use, provided that such content is in no way modified, and the credit for the source (NORD) and NORD’s copyright notice are included on the printed copy. Any other electronic reproduction or other printed versions is strictly prohibited.
Copyright 2006, 2012
NORD's Rare Disease Information Database is copyrighted and may not be published without the written consent of NORD.