Neural tube defects
Simply put, asphyxia is a lack of oxygen to the body. Asphyxia can have negative effects on all of the organs, including the brain. Asphyxia can occur in the womb, during delivery, or immediately after birth. Lack of oxygen, depending on how severe it is and how long it lasts, can have profound consequences to the brain and the rest of the body. At the same time, most babies can withstand a short period without oxygen without negative short or long-term effects. Most commonly, these short periods occur during labour and delivery or immediately following birth.
During pregnancy, some women develop high blood pressure and pre-eclampsia, or high blood pressure accompanied by a rapid swelling of the mother’s face, feet and hands. At times, pre-eclampsia can interfere with oxygen delivery to the fetus. If these types of events are of a short duration, the fetus will not likely face lasting damage. However, if these problems occur over a longer period of time, the baby’s brain may be damaged.
During birth, asphyxia may occur depending on how labour progresses. During labour, particularly a long and difficult one, oxygen flow to the unborn baby can be interrupted due to a squeezed umbilical cord or the placenta may become detached prematurely, cutting off the oxygen supply.
There are two treatments for asphyxia:
- hypothermic therapy, which produces a small deliberate drop in the baby’s temperature
- support, by encouraging improved oxygen delivery and blood circulation
Hypothermic therapy cools a baby’s brain cells by 3.5 degrees centigrade (about 6.5 F). This cooling slows down cell metabolism giving damaged brain cells time to recover.
When cells run out of oxygen, they can switch to a kind of emergency survival mode. The cells keep themselves alive by functioning with an abnormal metabolic process that does not use oxygen. However, this anaerobic metabolism can only be sustained for a short period of time. If the cell does not switch back to metabolizing oxygen to survive, it dies.
The problem is that simply restoring blood circulation and providing the normal amount of oxygen for the newborn at the earliest opportunity, is not enough to get the cells to immediately switch back to processing oxygen. The result is that many of the cells continue to die hours after the trauma is over.
Lowering the newborn’s temperature gives those cells the extra time they need to return to a normal metabolic process. Although the process is not completely understood, it is rather like the cold in the kitchen refrigerator slowing down the decay of perishable foods.
How soon cooling is started and how long the baby is cooled depends on how severe the asphyxia was. Some babies are cooled for 72 hours. There are no known negative short or long-term side effects of cooling. Most babies with asphyxia who are cooled avoid long-term disability.
Support consists of strategies to improve oxygen delivery within the body. Usually, this means delivering oxygen rather than air to the baby, often with mechanical ventilation. Additionally, blood circulation is monitored and, when necessary, improved by giving extra fluids, blood, or drugs to support heart function and blood pressure. A balance must be maintained; if blood pressure is too high, there is a risk of bleeding in the brain.
One of the prime functions of the brain is to send, interpret, and receive information. On the outside of the body, this information comes in the form of sight, sounds, smells, and so on. Within the brain, this information takes the form of electrical signals passed on by specialized cells called neurons. These signals are usually ordered: the body detects something hot, and the brain interprets the signal and sends another signal for the body to pull away. During a seizure, the brain misfires, sending overwhelming amounts of conflicting signals through the brain at the same time.
Seizures may be caused by asphyxia, a low blood sugar level, meningitis, bleeding within the brain, a stroke, a congenital malformation of the brain, or any cause of brain injury. Newborn babies with seizures will usually undergo brain imaging such as MRI or CT scan in order to see if there has been brain injury. It may not be possible to determine the cause of a baby’s seizure.
Treatment of seizures
Treatment of seizures depends on their severity and whether they are recurrent. Many infants may have a seizure or two but never have them again. If the problem is ongoing, there are several treatment options that can control the seizures.
Seizures consume a newborn baby’s energy at a high rate. If a newborn baby’s sugar level is low, glucose may be administered. Oxygen may also be given.
The primary medications given for seizures are a class of drug called anticonvulsants, which are also referred to as anti-epileptic drugs. These include phenobarbital, phenytoin, and lorazepam.
During anticonvulsant treatment, the newborn baby’s level of consciousness will be closely monitored. Generally, phenobarbital is tried first while a seizure is ongoing. If the newborn baby does not respond, phenytoin will be tried. Lorazepam is a relatively fast-acting agent that is generally administered when seizures are interfering with vital functions of the body and need to be stopped quickly.
The newborn baby will be monitored to ensure that the medication is working and to identify the lowest dosage that stops the seizures. Deciding when to stop treatment can be difficult and is in some ways a judgment call. The doctor must try to figure out at what point the seizures will not recur without the medication. Generally, anticonvulsant treatment is stopped before a newborn baby is ready to leave the NICU.
Any infection or metabolic imbalance will also be treated as this may be causing the seizures or making them worse.
Intraventricular hemorrhage or IVH is bleeding into the ventricles of the brain. This is primarily a problem in the premature infant. IVH is generally caused by physical injury, usually during labour, or by blood pressure changes that the immature blood vessels of the baby’s brain cannot cope with. It does not always imply brain injury, and may just mean that the newborn baby had a difficult transition around the time of birth.
Newborn babies with IVH will be handled with extra care. Additionally, close monitoring and perhaps manipulation of blood pressure will also be considered. However, if high blood pressure has caused an IVH or made it worse, blood pressure cannot simply be lowered because there would be a risk of asphyxia with such a treatment. In most cases of IVH, the bleeding gradually stops and the blood vessels heal themselves.
It is often difficult to tell whether brain damage has occurred in the premature baby. Many newborn babies with IVH seem to have no evidence of brain damage when they are older, while other newborn babies with relatively minor bleeds may have suffered significant brain injury. Unfortunately, often the only way to tell if there has been brain damage is to wait and see what the baby does when he gets older. Usually by the age of two years an experienced paediatrician or neonatologist can make that judgement.
Treatment of IVH
In more severe cases of IVH, other treatments may be necessary. At times, the bleeding and the pressure within the ventricles can interfere with the flow of cerebrospinal fluid or CSF. This, in turn, may cause a condition called hydrocephalus, where there is a build-up of CSF in the ventricles of the brain. The treatment of hydrocephalus may involve the surgical placement of a shunt, which is a thin tube that drains the CSF from the brain to another part of the body such as the abdomen. Prior to surgery, CSF may be drained off to relieve pressure in the ventricles.
Whenever there is bleeding into the brain or between the brain and the skull, significant damage and brain injury are likely. Further tests such as CT scan and MRI may be required, and subspecialty physicians may be needed to help babies in these rare circumstances.
Neural tube defects
The central nervous system starts to develop in week five of pregnancy. At that time, a thickening of cells called the neural plate forms, which folds in on itself to create what we know as the neural tube. One end of the neural tube will form the brain, and the remainder of the neural tube will form the spinal cord. In week six, openings in the neural tube close. If these openings do not close properly, abnormalities called neural tube defects can form. These defects are rare, but they account for most of the abnormalities of the brain and spinal cord.
Neural tube defects affecting the brain
Encephaloceles are when parts of the brain protrude through openings in the skull. The protruding parts of the brain are encased in a sac. Usually, encephaloceles are dramatic deformities associated with neurological problems. They are often associated with abnormalities of the brain, skull, face, and other problems. Some examples of these abnormalities include:
- an abnormally small head, called microcephaly
- paralysis of the arms and legs
- uncoordinated movements
- a build-up of cerebrospinal fluid within the brain, called hydrocephalus
- developmental delay
- intellectual disability, although some children with encephaloceles have normal intelligence
- vision problems
Encephaloceles are usually treated with surgery to place the tissues back into the skull and correct any facial abnormalities. Hydrocephalus may be treated with a shunt, which is a thin tube that drains out the extra cerebrospinal fluid from within the brain to the abdominal cavity.
Anencephaly is the absence of a major part of the brain, skull, and scalp. A baby born with anencephaly is usually blind, deaf, unconscious, and unable to feel pain. He may still be able to breathe and respond to sound or touch. The prognosis for babies born with anencephaly is extremely poor. If the baby is born alive he will usually die within a few hours or days after birth.
Hydranencephaly is a condition where the cerebral hemispheres of the brain are missing and replaced by sacs of cerebrospinal fluid. A newborn baby with hydranencephaly may appear normal at birth and have spontaneous reflexes such as sucking, crying, and swallowing. He may move his arms and legs normally. His head size may appear normal. However, after a few weeks, the baby usually becomes irritable and his muscles may start to tense more and more. He may develop seizures and hydrocephalus, where there is a build-up of cerebrospinal fluid in the brain. He may be deaf, blind, paralyzed, and have intellectual problems. Some babies with this condition also have respiratory problems. Most children with this condition die before the age of one year. Some children with hydranencephaly may survive for a few years.
Arnold-Chiari malformation is a condition where a part of the brain protrudes into the spinal canal. Arnold-Chiari malformation can cause symptoms of headache, vomiting, difficulty swallowing, and hoarseness. Another symptom is hydrocephalus, which can be corrected with a shunt to drain the cerebrospinal fluid from within the brain. Some babies with this condition have a defect of the spine called myelomeningocele, which is more commonly known as spina bifida.
Neural tube defects affecting the spine
Spina bifida is the most common permanently disabling birth defect. In spina bifida, there are abnormalities of the spinal cord because the neural tube did not close properly during early pregnancy. This abnormality affects every person differently, and varies in its severity. People with spina bifida may have some of the following symptoms:
- weakness or paralysis of the legs
- hydrocephalus: a build-up of cerebrospinal fluid in the brain, which causes the brain to swell
- problems controlling bowel movements
- learning disabilities
There are different types of spina bifida. Spina bifida occulta, a mild condition, is when the spinal cord is normal with no openings to the back. There may be a small gap in some of the small bones that make up the spine. Although there may be no motor and sensory problems at birth, there may be subtle neurological deterioration later in childhood or as the child grows into adulthood.
Spina bifida cystica, on the other hand, is a severe condition where the protective coating of the spinal cord comes through the openings in the spine. This causes a sac filled with cerebrospinal fluid to protrude through the back. In rare cases, spinal nerves may also protrude into the sac outside the back. This can cause nerve damage and severe disabilities, but usually not intellectual disability.
If a baby is born with spina bifida where the spinal cord protrudes through the back, the spinal opening will be surgically closed, usually within the first 24 hours of life. This is done to minimize the risk of infection and preserve the existing function of the spinal cord.
Many people with spina bifida require assistive devices such as wheelchairs, crutches, or braces in order to move around. They may also need additional surgery, medications, and physiotherapy. Other ongoing therapy and medical care may be necessary for the prevention and management of complications that may arise throughout the person’s life.
Preventing, screening, and diagnosing neural tube defects
The risk of neural tube defects can be reduced if the mother takes adequate amounts of folic acid before becoming pregnant and during the first trimester of pregnancy.