Overview of Congenital Neurologic Anomalies

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 , 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 ), 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.

Amniocentesis Amniocentesis All procedures used to diagnose genetic disorders, except ultrasonography, are invasive and involve slight fetal risk. If testing detects a serious abnormality, the pregnancy can be terminated... read more and ultrasonography Prenatal Ultrasonography All procedures used to diagnose genetic disorders, except ultrasonography, are invasive and involve slight fetal risk. If testing detects a serious abnormality, the pregnancy can be terminated... read more permit accurate in utero detection of many malformations, and newer fetal MRI techniques are increasingly useful. Parents need psychologic support when a malformation is detected and also genetic counseling, because the risk of having a subsequent child with such a malformation is high.