Overview of Congenital Neurologic Anomalies

Congenital brain anomalies cause a spectrum of neurologic deficits; although some may be barely noticeable, others may be fatal.

Some of the most serious neurologic anomalies (eg, anencephaly Anencephaly Anencephaly is absence of the cerebral hemispheres. It is usually accompanied by a defect in the formation of the skull posteriorly, leaving the back of the head without skeletal protection... read more , encephalocele Encephalocele An encephalocele is a protrusion of nervous tissue and meninges through a skull defect. Many can be repaired surgically. An encephalocele is caused by incomplete closure of the cranial vault... read more , spina bifida Spina Bifida Spina bifida is defective closure of the vertebral column. Although the cause is often unknown, low folate levels during pregnancy increase risk. Some children are asymptomatic, and others have... read more ) develop in the first 2 months 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 weeks and 24 weeks of gestation. Hydranencephaly Hydranencephaly Porencephaly is a cavity that develops prenatally or postnatally in a cerebral hemisphere. Cavities often communicate with a ventricle, but they may also be enclosed (ie, noncommunicating) fluid-filled... read more and porencephaly Porencephaly Porencephaly is a cavity that develops prenatally or postnatally in a cerebral hemisphere. Cavities often communicate with a ventricle, but they may also be enclosed (ie, noncommunicating) fluid-filled... 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. Next-generation sequencing techniques Genetic Diagnostic Technologies , such as genetic panels and whole exome sequencing, have revealed a large number of genetic causes of these anomalies.

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 can be used to accurately screen for many malformations in utero. Newer fetal MRI techniques are increasingly useful, mainly when ultrasound findings are of concern. Amniocentesis can be used to find larger chromosomal rearrangements and breakage but often misses more subtle genetic causes of congenital anomalies.

Parents often need psychologic support when a malformation is detected and also genetic counseling Prenatal Genetic Counseling Prenatal genetic counseling is provided for all prospective parents, ideally before conception, to assess risk factors for congenital disorders. Precautions to help prevent birth defects (eg... read more , because the risk of having a subsequent child with such a malformation may be high.