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Overview of Congenital Neurologic Anomalies

By

Stephen J. Falchek

, MD, Nemours/Alfred I. duPont Hospital for Children

Last full review/revision Dec 2018| Content last modified Dec 2018
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Congenital brain anomalies usually cause severe neurologic deficits; some may be fatal.

Some of the most serious neurologic anomalies (eg, anencephaly Anencephaly Anencephaly is absence of the cerebral hemispheres. The absent brain is sometimes replaced by malformed cystic neural tissue, which may be exposed or covered with skin. Parts of the brain stem... read more , encephalocele Encephalocele An encephalocele is a protrusion of nervous tissue and meninges through a skull defect. An encephalocele is caused by incomplete closure of the cranial vault (cranium bifidum). Encephaloceles... read more , spina bifida Spina Bifida Spina bifida is defective closure of the vertebral column. Although the cause is not known, low folate levels during pregnancy increase risk. Some children are asymptomatic, and others have... read more ) develop in the first 2 mo of gestation and represent defects in neural tube formation (dysraphism). Others, such as lissencephaly Lissencephaly Cerebral hemispheres may be large, small, or asymmetric; the gyri may be absent, unusually large, or multiple and small. In addition to the grossly visible malformations, microscopic sections... read more Lissencephaly , result from problems with neuronal migration (see Malformed Cerebral Hemispheres Malformed Cerebral Hemispheres Cerebral hemispheres may be large, small, or asymmetric; the gyri may be absent, unusually large, or multiple and small. In addition to the grossly visible malformations, microscopic sections... read more Malformed Cerebral Hemispheres ), which occurs between 9 wk and 24 wk of gestation. Hydranencephaly Hydranencephaly Porencephaly is a cavity that may develop prenatally or postnatally in a cerebral hemisphere. Cavities often communicate with a ventricle, but they may also be enclosed (ie, noncommunicating)... read more and porencephaly Porencephaly Porencephaly is a cavity that may develop prenatally or postnatally in a cerebral hemisphere. Cavities often communicate with a ventricle, but they may also be enclosed (ie, noncommunicating)... read more are secondary to destructive processes that occur after the basic architecture of the brain has formed. Some anomalies (eg, meningocele) may be relatively benign.

There are many causes of congenital brain anomalies, including many previously unknown genetic factors.

Prevention of Congenital Neurologic Anomalies

Women who have had a fetus or infant with a neural tube defect are at high risk and should take folate Folate Deficiency Folate deficiency is common. It may result from inadequate intake, malabsorption, or use of various drugs. Deficiency causes megaloblastic anemia (indistinguishable from that due to vitamin... read more (folic acid) supplementation 4 mg (4000 mcg) po once/day beginning 3 mo before conception and continuing through the 1st trimester. Folate supplementation reduces the risk of neural tube defects in future pregnancies by 75%.

All women of childbearing age who have not had a fetus or infant with a neural tube defect should consume at least 400 mcg/day of folate through diet or by taking a supplement (some experts recommend 800 mcg/day to further reduce risk) and continue doing so through the 1st trimester. Although folate supplementation reduces the risk of having a child with a neural tube defect, risk reduction is less than in women who previously had a fetus or infant with a neural tube defect (ie, risk reduction is < 75%).

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