Cerebral palsy is caused by damage to parts of the brain that occurs before birth, during birth, or shortly after birth.
The exact causes of cerebral palsy may be unclear, but factors include:
- A maternal infection in early pregnancy
- Abnormally high or low blood pressure in the mother during pregnancy
- Premature birth – especially if a baby is born at 32 weeks or earlier because these babies are vulnerable to haemorrhage, infection and oxygen deprivation
- A difficult birth that causes injury to a baby’s head or restricts oxygen supply
- Illness or injury to the baby after birth, such as meningitis, head injury, high fever or restricted oxygen (from choking or suffocating), untreated hypoglycaemia, untreated jaundice
- Inherited genetic disorders.
These factors can lead to:
- Damage of the brain’s white matter or periventricular leukomalacia (PVL)
- Intracranial haemorrhage and stroke
- Abnormal development of the brain.
When you talk to your doctor, paediatrician or specialist legal team about the possible causes of cerebral palsy, they may use complex terms and explanations.
Below we provide more detail about the causes cerebral palsy and of brain injury, and explain the medical terms often used:
What is hypoxic-ischaemic brain injury?
At all stages of life, the brain has enormous energy demands. Most of the energy is produced from a chemical reaction involving glucose and oxygen. Brain cells have poor energy storage facilities and as a result, the brain depends on a second-by-second supply of glucose and oxygen.
Oxygen and glucose are transported to the brain via blood circulating around the body. A drop in blood oxygen (hypoxia); a drop in blood glucose (hypoglycaemia); and/or a disruption in blood flow (ischaemia) can all result in energy deprivation.
Hypoxic-ischaemia describes an insult (injury) caused by any combination of the above.
When the brain is deprived of energy, the result is brain cell injury and brain cell death. The pattern of brain injury in hypoxic-ischaemia will depend on the severity and duration of the insult. In foetuses and babies, the pattern of brain injury will also depend on the maturity of the brain.
What is perinatal hypoxic-ischaemia?
Perinatal refers to the short period before, during and after birth, and this is a risky time for suffering brain damage as a result of hypoxic-ischaemia. For example, if the umbilical cord is compressed during birth, it could disrupt blood flow to the baby’s brain. Or a difficult delivery may put too much strain on the baby’s cardiovascular system.
The pattern of brain injury will depend upon the severity and duration of the disruption, and on the maturity of the brain.
What is acute near total hypoxic-ischaemia?
Acute near total hypoxic-ischaemia describes a situation whereby the energy deprivation is sudden and severe. In babies born at term, the areas of the brain most affected by this type of injury are the deep structures of the brain including the basal ganglia, thalamus and brain stem.
The reason that this area of the brain is vulnerable to energy deprivation is because at this stage of a baby’s life, the brain cells of these deep structures have the highest energy demands in the brain.
The basal ganglia, thalamus and brain stem are involved with the coordination of movement. Children with this pattern of injury are likely to be severely disabled with movement disorders and in particular, athetoid cerebral palsy.
What is chronic partial hypoxic-ischaemia?
Chronic partial hypoxic-ischaemia happens when the energy deprivation is prolonged and only partial in severity. The different arteries of the brain supply blood to different territories of the brain. In mature infants, the brain cells within the border zones between these territories are the most vulnerable to this type of injury, and therefore chronic partial hypoxic-ischaemia results in damage to the outer reaches of the brain or the cortex.
Children with this pattern of injury are likely to demonstrate symptoms of developmental delay and behavioural problems.
What is periventricular leukomalacia and its impact?
Periventricular leukomalacia (PVL) is a form of brain damage affecting the area of the brain either side of two reservoir-like chambers known as the lateral ventricles. It is also known as white matter damage. In premature infants, this area of the brain is particularly vulnerable to the effects of both energy deprivation and infection, because the cells in this part of the brain have not yet developed their main defence mechanisms.
In premature infants, PVL is a pattern of injury seen in both acute near total hypoxic-ischaemia and chronic partial hypoxic-ischaemia.
Children who suffer from PVL may experience a wide range of problems depending on the severity of the injury. While some children may experience only minor disabilities in movement, a more severe injury may result in cerebral palsy and/or epilepsy.
How do maternal infections cause chorioamnionitis and brain injury?
Chorioamnionitis arises when the membranes and amniotic fluid surrounding the fetus become infected. This can arise when bacteria or other infective organisms travel from the vagina up in to the uterus, causing infection within the uterus and subsequent infection of the fetus.
Normally the fetus is protected from infection by a plug of mucus that sits in the cervix and by the membranes that surround it, but once rupture of membranes has occurred, the fetus is much more vulnerable to infection.
Occasionally the infective organisms reach the uterus by travelling across the placenta, or they can enter the uterus during invasive procedures such as amniocentesis.
Once the fetus becomes infected, the bacteria can travel to the brain where it can cause an infection of the membranes surrounding the brain, otherwise known as meningitis (see below).
How does maternal Group B Streptococcus infection go on to cause brain injury?
Group B Streptococcus (GBS) is a type of bacteria that can cause chorioamnionitis. GBS is part of the normal flora of the vagina so most mothers who carry GBS are not aware that they carry it.
Like other types of bacteria, GBS can travel into the uterus from the vagina to cause chorioamnionitis and subsequent infection of the fetus. Alternatively babies can become infected with GBS during delivery.
Once the fetus or baby becomes infected with GBS the bacteria can travel to the brain where it can cause an infection of the membranes surrounding the brain, otherwise known as meningitis (see below).
What is meningitis and how does it cause brain injury?
Meningitis is an infection of the meninges, the three layers of membrane that envelop the brain and the spinal cord.
The outermost layer lies under the skull. It is a thick membrane known as the dura mater, which literally means ‘tough mother’. The next layer is the arachnoid mater, which looks a bit like a spider’s web, hence the reference to ‘arachnoid’. The final layer, which lies over the brain itself, is the pia mater, which can be translated as ‘gentle mother’. Between the arachnoid mater and the pia mater is the arachnoid space. The arachnoid space is full of cerebrospinal fluid (CSF), a watery substance that circulates around the brain.
The lining of blood vessels within the brain is thicker than elsewhere in the body, providing a protective barrier (the blood-brain-barrier) between the circulating blood and the brain itself. It allows essential nutrients to pass through the lining but blocks harmful organisms.
Various types of viruses and bacteria can infect the meninges. In newborn babies, meningitis is commonly caused by streptococcus group B and E coli bacteria.
The bacteria may spread to the meninges from an adjacent infected area, or via the blood stream, penetrating the brain where the blood-brain-barrier is weak.
In some situations, for example where there is a congenital abnormality or where there has been a surgical procedure to the brain, the bacteria can reach the meninges by direct contact between the meninges and the outside world.
Once bacteria enters the cerebrospinal fluid, it can spread and multiply quickly.
Brain damage in bacterial meningitis is caused by the toxins released from the bacteria and also by the body’s own response to infection.
Toxins released from the bacteria damage brain cells but also cause damage to blood vessels, leading to a lack of blood (ischaemia) and energy reaching the brain cells.
When the bacteria are detected by the immune system, the immune system releases chemical messengers called cytokines, which in turn attract white blood cells. The white blood cells ingest the bacteria, but the process of ingesting the bacteria leads to the release of toxins that can damage both brain cells and blood vessels.
So although the immune system serves to protect the brain and body, the system starts a destructive cascade that can cause as much damage to the brain as the bacteria it aims to eliminate.
Children who have suffered from meningitis may experience different types of brain damage, depending on which areas of the brain were affected. This can result in cerebral palsy, epilepsy, hearing loss and intellectual difficulties.
What is hypoglycaemia and what is its impact on the brain?
At all stages of life, the brain has enormous energy demands. Most of the energy is produced from a chemical reaction involving glucose (sugar) and oxygen.
Brain cells have poor energy storage and as a result, the brain depends on a second-by-second supply of glucose and oxygen. Oxygen and glucose are transported to the brain via blood circulating around the body. A drop in blood oxygen (hypoxia); a drop in blood glucose (hypoglycaemia); and/or a disruption in blood flow (ischaemia) can all result in energy deprivation.
Under normal conditions, the body carefully maintains levels of blood glucose. When blood glucose levels rise, glucose is turned into glycogen that can be stored in the body. This reduced the amount of glucose in the blood and blood glucose levels are restored. Conversely, when blood glucose levels drop, glycogen is turned back into glucose, and blood glucose levels are maintained.
Hypoglycaemia is when levels of blood glucose are too low. Premature babies (and newborns) are particularly vulnerable to hypoglycaemia because they have deficient glycogen stores. Other causes of hypoglycaemia include a simple lack of blood glucose due to inadequate feeding or too much insulin. This causes poor regulation of blood glucose levels by turning too much glucose into glycogen.
When the brain is deprived of energy, the result is brain cell injury and brain cell death. The pattern of brain injury in hypoglycaemia will depend on the severity and duration of the insult. Babies who have suffered from hypoglycaemia may go on to suffer from developmental delay, epilepsy and cerebral palsy.
What is microcephaly and what is its impact on the brain?
Microcephaly describes a head that is smaller than normal because the brain has not developed properly. Most cases of microcephaly have a genetic cause but microcephaly may be caused by brain injury as a result of hypoxic-ischaemia or infection.
Microcephaly is sometimes the first indication that a baby has suffered from an infection or a period of hypoxic-ischaemia (energy deprivation) affecting the brain.
The impact of microcephaly will depend upon the nature of the injury to the brain. Babies and children who have microcephaly may go on to suffer from developmental delay, epilepsy and cerebral palsy.
What is intrauterine growth restriction and its impact?
Intrauterine growth restriction (IUGR) refers to poor growth of a foetus while in the mother’s womb during pregnancy.
Foetuses require energy for development and growth. Most of the energy is produced from a chemical reaction involving glucose (sugar) and oxygen, delivered to the baby from the placenta via the umbilical vein.
A drop in blood oxygen (hypoxia); a drop in blood glucose (hypoglycaemia); and/or a disruption in blood flow (ischaemia) can all result in energy deprivation to the developing foetus and the rate of growth is reduced.
The causes can be many, but most often involve poor maternal nutrition or anaemia. When the energy deprivation occurs in the first and/or second trimester of pregnancy, the development of the brain is particularly affected. When the energy deprivation occurs in the third trimester of pregnancy, by this time most brain cells are already developed and the affects on the brain are less severe. Children who have suffered from IUGR may experience memory and learning difficulties.
What is intraventricular haemorrhage or ‘germinal matrix haemorrhage’, and its impact?
An intraventricular haemorrhage occurs when blood escapes into the ventricles of the brain. The brain is surrounded by cerebrospinal fluid (CSF) that circulates around the brain and through reservoir like structures known as the ventricles.
Once blood escapes into the ventricles, blood clots may prevent the circulation of CSF around the brain. The ventricles may expand, causing damage to the surrounding brain tissue. The accumulation of fluid within the brain leads to a condition known as hydrocephalus. In the worst-case scenario, the build-up of CSF increases intra-cranial pressure to such an extent that the patient dies.
Perinatal intraventricular haemorrhage can occur at any time but usually develops a few hours after birth. Premature babies are most vulnerable to intraventricular haemorrhage because the developing brain still contains a thick layer of immature cells under the lining of the ventricles. This layer of cells is called the germinal matrix.
The germinal matrix is fragile and has an abundant blood supply. When it is damaged as a result of hypoxic ischaemia, infection or occasionally trauma, blood escapes into the ventricles of the brain.
Children who have suffered from intraventricular haemorrhage may experience developmental delay and cerebral palsy.
The terms ‘germinal matrix haemorrhage’ and ‘intraventricular haemorrhage’ are commonly interchangeable in premature babies.
What is kernicterus (bilirubin encephalopathy) and what is its impact on the brain?
Bilirubin is a product of the breakdown of red blood cells. When red blood cells are first broken down, the bilirubin that is produced is insoluble in water and is referred to as ‘unconjugated bilirubin’.
Unconjugated bilirubin then travels to the liver where it is converted into conjugated bilirubin that is soluble in water. This process enables it to be readily excreted from the body in faeces or in urine. The enzyme responsible for converting unconjugated bilirubin into conjugated bilirubin is called glucoronyl transferase.
Bilirubin can build up in the body when either too much of it is being formed (usually due to an increase in red blood cell breakdown) or because the body is having difficulty getting rid of it, e.g. there is a problem with the conversion of unconjugated bilirubin into the water-soluble conjugated bilirubin.
Kernicterus (bilirubin encephalopathy) is caused by the build-up of unconjugated bilirubin and can occur in newborn babies either as a result of a blood disorder leading to the breakdown of too many red blood cells, or because the liver cannot convert bilirubin to its water-soluble state. The latter is more common in premature babies who lack glucoronyl transferase, the enzyme required to conjugate bilirubin.
The unconjugated bilirubin is able to cross from the blood into the brain where it is able to bind to brain cell membranes and exert its toxic effects on the brain cell, resulting in cell death.
Bilirubin has a particular affinity for the deep areas of the brain responsible for voluntary movement and this is why a brain injury due to excess bilirubin can lead to cerebral palsy. Bilirubin-induced brain damage can also result in developmental delay and hearing problems.