hemimegalencephaly

{{short description|Disorder affecting development of one side of the brain}}

{{Infobox medical condition (new)

| name = Hemimegalencephaly

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| image = OJO-7-43-g005.jpg

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| caption = Left-sided hemimegalencephaly in a person with neurofibromatosis{{cite journal |vauthors=Acharya N, Reddy MS, Paulson CT, Prasanna D |title=Cranio-orbital-temporal neurofibromatosis: an uncommon subtype of neurofibromatosis type-1 |journal=Oman Journal of Ophthalmology |volume=7 |issue=1 |pages=43–5 |date=January 2014 |pmid=24799805 |pmc=4008903 |doi=10.4103/0974-620X.127934 |url= |doi-access=free }}

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| symptoms =Frequent seizures often resistant to medicine

| complications =

| onset =Congenital

| duration =Long term

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| prevention =

| treatment =Hemispherectomy

| medication =Anti-epileptic drugs

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}}

Hemimegalencephaly (HME), or unilateral megalencephaly, is a rare congenital disorder affecting all or a part of a cerebral hemisphere.{{cite journal|last1=Sato|first1=N|last2=Yagishita|first2=A|last3=Oba|first3=H|last4=Miki|first4=Y|last5=Nakata|first5=Y|last6=Yamashita|first6=F|last7=Nemoto|first7=K|last8=Sugai|first8=K|last9=Sasaki|first9=M|title=Hemimegalencephaly: a study of abnormalities occurring outside the involved hemisphere.|journal=AJNR. American Journal of Neuroradiology|date=April 2007|volume=28|issue=4|pages=678–82|pmid=17416820|pmc=7977333|url=http://www.ajnr.org/content/28/4/678}} It causes severe seizures, which are often frequent and hard to control. A minority might have seizure control with medicines, but most will need removal or disconnection of the affected hemisphere as the best chance. Uncontrolled, they often cause progressive intellectual disability and brain damage and stop development.{{Cite web|url=https://www.brainrecoveryproject.org/for-parents/when-to-ask-for-a-surgical-evaluation/your-child-has-a-likely-drug-resistant-condition/hemimegalencephaly/|title=Hemimegalencephaly - Why hemispherectomy is usually required|website=www.brainrecoveryproject.org|language=en-US|access-date=2018-04-12}}

Symptoms and signs

Seizures are the main symptom. There can be as many as hundreds of seizures a day.{{Cite web|url=https://health.ucsd.edu/news/releases/Pages/2012-25-hemimegalencephaly.aspx|title=Gene Mutations Cause Massive Brain Asymmetry|website=UC Health - UC San Diego|language=en-US|access-date=2018-04-12}} Seizures tend to begin soon after birth, but may sometimes commence during later infancy or, rarely, during early childhood.{{Cite web|url=http://hemifoundation.homestead.com/hemimegalencephaly.html|title=Hemimegalencephaly & Cortical Dysplasia|website=hemifoundation.homestead.com|access-date=2018-04-14}}

= Other symptoms =

Asymmetrical or enlarged head
Developmental delay
Progressive weakness of half the body
Progressive blindness of half the body

Genetics

Somatic activation of AKT3 causes hemispheric developmental brain malformations.{{cite journal|last1=Poduri|first1=Annapurna|last2=Evrony|first2=Gilad D.|last3=Cai|first3=Xuyu|last4=Elhosary|first4=Princess Christina|last5=Beroukhim|first5=Rameen|last6=Lehtinen|first6=Maria K.|last7=Hills|first7=L. Benjamin|last8=Heinzen|first8=Erin L.|last9=Hill|first9=Anthony|last10=Hill|first10=R. Sean|last11=Barry|first11=Brenda J.|last12=Bourgeois|first12=Blaise F.D.|last13=Riviello|first13=James J.|last14=Barkovich|first14=A. James|last15=Black|first15=Peter M.|last16=Ligon|first16=Keith L.|last17=Walsh|first17=Christopher A.|title=Somatic Activation of AKT3 Causes Hemispheric Developmental Brain Malformations|journal=Neuron|date=April 2012|volume=74|issue=1|pages=41–48|doi=10.1016/j.neuron.2012.03.010|pmid=22500628|pmc=3460551}}

Pathophysiology

It is a disorder related to excessive neuronal proliferation and hamartomatous overgrowth affecting the cortical formation.{{cite journal|last1=Abdel Razek|first1=A.A.K.|last2=Kandell|first2=A.Y.|last3=Elsorogy|first3=L.G.|last4=Elmongy|first4=A.|last5=Basett|first5=A.A.|title=Disorders of Cortical Formation: MR Imaging Features|journal=American Journal of Neuroradiology|date=7 August 2008|volume=30|issue=1|pages=4–11|doi=10.3174/ajnr.A1223|pmid=18687750|pmc=7051699|doi-access=free}} The excessive proliferation is postulated to occur early and to possibly continue beyond the normal proliferative period. Epidermal growth factor is thought to play an important role in the excessive proliferation and the pathogenesis of HME.{{cite book|author1=Harvey B. Sarnat|author2=Paolo Curatolo|title=Malformations of the Nervous System|url=https://books.google.com/books?id=XzwNPUW2ucgC&pg=PA154|date=26 September 2007|publisher=Newnes|isbn=978-0-08-055984-1|pages=154}}

Diagnosis

It should be suspected in infants or children with intractable, frequent seizures. On a CT scan, the affected part is distorted and enlarged.{{Cite web|url=http://www.latimes.com/health/la-me-dylan-html-htmlstory.html|title=Radical surgery offers hope for baby racked by seizures|last=Hennessy-Fiske|first=Molly|website=Los Angeles Times|access-date=2018-04-12|date=2012-06-15}} It can be diagnosed prenatally, but a lot of cases go undiagnosed until seizures begin. Ultrasound can display asymmetrical brain hemispheres.

Treatment

Although there have been a few reports of medical treatment, the main treatment is radical: remove or disconnect the affected side. However, it has a high mortality [recent citations needed], and there have been reports of a vegetative state and seizures resuming, this time in the healthy hemisphere.{{Cite journal|last1=Bonioli|first1=Eugenio|last2=Palmieri|first2=Antonella|last3=Bellini|first3=Carlo|date=1994-03-01|title=Surgical vs. medical treatment of seizures in hemimegalencephaly|url=http://www.brainanddevelopment.com/article/0387-7604(94)90060-4/fulltext|journal=Brain and Development|language=English|volume=16|issue=2|pages=169|doi=10.1016/0387-7604(94)90060-4|pmid=8048711|s2cid=2442788|issn=0387-7604}}

Surgery is usually performed as soon as possible to minimize damage caused by seizures. However, a trial with drugs can be attempted for a few months before surgery, and there is a slim chance of it succeeding. Because brain plasticity decreases with age, the earlier in life the surgery is completed, the more likely it is that the remaining hemisphere will adapt to perform tasks previously completed by the missing hemisphere.

Benzodiazepines might control the seizures.{{Cite journal|title=Hemimegalencephaly: diagnosis and treatment. - Semantic Scholar|year=1991|doi=10.1111/j.1469-8749.1991.tb05116.x|pmid=1902803|s2cid=45836490|last1=Trounce|first1=J. Q.|last2=Rutter|first2=N.|last3=Mellor|first3=D. H.|journal=Developmental Medicine and Child Neurology|volume=33|issue=3|pages=261–6}}