There are two classes of<unk> s: open, which are more common, and closed. Open<unk> s occur when the brain and/or spinal cord are exposed at birth through a defect in the skull or vertebrae (spinal column). Open<unk> s include anencephaly, encephaloceles, hydranencephaly, iniencephaly, schizencephaly, and the most common form, spina bifida. Closed<unk> s occur when the spinal defect is covered by skin. Types of closed<unk> s include lipomeningocele, lipomyelomeningocele, and tethered cord. Anencephaly Anencephaly (without brain) is a severe<unk>  that occurs when the anterior-most end of the<unk> <unk>  fails to close, usually during the 23rd and 26th days of pregnancy. This results in an absence of a major portion of the brain and skull. Infants born with this condition lack the main part of the forebrain and are usually blind, deaf and display major craniofacial anomalies. The lack of a functioning cerebrum will prevent the infant from even gaining consciousness. Infants are either stillborn or usually die within a few hours or days after birth. For example, anencephaly in humans can result from mutations in the NUAK2 kinase. Encephaloceles Encephaloceles are characterized by protrusions of the brain through the skull that are sac-like and covered with membrane. They can be a groove down the middle of the upper part of the skull, between the forehead and nose, or the back of the skull. Due to the range in its location, encephaloceles are classified by the location as well as the type of defect it causes. Subtypes include occipital encephalocele, encephalocele of the carnival vault, and nasal encephaloceles (frontoethmoidal encephaloceles and basal encephaloceles), with approximately 80% of all encephaloceles occurring in the occipital area. Encephaloceles are often obvious and diagnosed immediately. Sometimes small encephaloceles in the nasal and forehead are undetected. Despite the wide range in its implications, encephaloceles are most likely to be caused by improper separation of the surface ectoderm and the neuroectoderm after the closure of the<unk>  folds in the fourth week of gastrulation. Hydranencephaly Hydranencephaly is a condition in which the cerebral hemispheres are missing and instead filled with sacs of cerebrospinal fluid. People are born with hydranencephaly, but most of the time, the symptoms appear in a later stage. Newborns with hydrancephaly can swallow, cry, sleep and their head is in proportion to their body. However, after a few weeks, the infants develop increased muscle tone and irritability. After a few months, the brain start to fill with cerebrospinal fluid (hydrocephalus). This has several consequences. Infants start to develop problems with seeing, hearing, growing, and learning. The missing parts of the brain and the amount of cerebrospinal fluid can also lead to seizures, spasm, problems with regulating their body temperature, and breathing and digestion problems. Besides problems in the brain, hydranencephaly can also be seen on the outside of the body. Hydrocephalus leads to more cerebrospinal fluid in the brain, which can result in an enlarged head. The cause of hydranencephaly is not clear. Hydranencephaly is a result of an injury of the nervous system or an abnormal development of the nervous system. The<unk> <unk>  closes in the 6th week of the pregnancy, so hydranencephaly develops during these weeks of the pregnancy. The cause of these injuries/development is not clear. Theories regarding the causes of hydrancephaly include: * blockage in the carotid artery: some researchers think that a blockage of the carotid artery leads to the under-/no development of the brain. The carotid artery is the most important blood supplier of the brain. With a blockage, the brain barely receives blood. Blood is necessary for development and keeping intact of the brain. * inherited condition. * infections: during the pregnancy, a woman can develop an infection in the uterus what can lead to problems with the<unk> <unk> . * environmental toxins: during the pregnancy, a woman can be exposed to environmental toxins what can have effect on the health of the infant. Iniencephaly Iniencephaly is a rare<unk>  that results in extreme bending of the head to the spine. The diagnosis can usually be made on antenatal ultrasound scanning, but if not will undoubtedly be made immediately after birth because the head is bent backwards and the face looks upwards. Usually the neck is absent. The skin of the face connects directly to the chest and the scalp connects to the upper back. Individuals with iniencephaly generally die within a few hours after birth. Spina bifida Spina bifida is further divided into two subclasses, spina bifida cystica and spina bifida occulta. * Spina bifida cystica includes meningocele and myelomeningocele. Meningocele is less severe and is characterized by herniation of the meninges, but not the spinal cord, through the opening in the spinal canal. Myelomeningocele involves herniation of the meninges as well as the spinal cord through the opening. * Spina bifida occulta means hidden split spine. In this type of<unk> , the meninges do not herniate through the opening in the spinal canal. The most frequently seen form of spina bifida occulta is when parts of the bones of the spine, called the spinous process, and the<unk>  arch appear abnormal on a radiogram, without involvement of the spinal cord and spinal nerves. The risk of recurrence in those who have a first degree relative (a parent or sibling) is 5–10 times greater compared to the general population.
Neural tube defect
Birth defect
Congenital limb deformities
Craniofacial abnormality
Vocal cord dysfunction
Neonatal sepsis
Perinatal asphyxia
Renal hypoplasia