The developing brain of a preterm infant is also vulnerable to injury. There are several types of problems that affect the developing preemie brain.

The brain and the spinal cord, called the central nervous system, begin to develop very early, around the third week, in pregnancy and continues until way after birth. The surface of the brain develops quickly between weeks 24 and 40, and so there is a big difference between the brain of a preemie born less than 28 weeks gestation and a baby born later than 32 weeks.

Getting an Idea about the Brain

It can be difficult to understand all the terminology and details about the brain at the best of times, but it is especiallyl difficult when your baby has had a bleed of some kind. The following information should give you a bit of an idea about the brain before you try and understand what has happened if your preemie has had a bleed. Go through the information slowly and make note of any questions you may have, so that you can ask your doctor at your next appointment.

The outer layer of the brain called the cerebral cortex, or gray matter, consists of millions of neurons that are responsible for thinking, learning, and storing memories. Underneath the gray matter is white matter, which consists of millions of axons. Axons carry electrical messages between neurons and into the spinal cord. Deep within the brain are a series of chambers that are called ventricles. The brain and spinal cord are protected by a clear fluid, called cerebrospinal fluid, produced within the ventricles. The germinal matrix is near the ventricles and makes new neurons and cells that support them, it is also called the subependymal region. If you have ever seen a picture of a brain, you will notice that it has many wrinkles or grooves that look like folds, these folds increase the surface area of the brain and help it function more powerfully and efficiently. In other words, the folds are very important for learning and intelligence. The process of folding occurs between 24 and 40 weeks gestation so a premature baby born around 24 weeks gestation will have a brain that would look smooth on the surface, whereas a baby born at term would have a brain with grooves and folds. Because a preterm infant is born during a time the brain is undergoing important developmental changes, it is vulnerable to injury.

Brain Haemorrhage: Intraventricular Ventricular Haemorrhage & Germinal Matrix Haemorrhage

A brain hemorrhage, or bleeding within a premature infant’s brain are of 2 types, they are intraventricular and germinal matrix haemorrhages. The preterm infant has a number of physiological features that make it vulnerable to brain injury. Blood vessels in the germinal matrix carry a large amount of blood and are very fragile. These fragile vessels in the inner part of a preemies brain are vulnerable to changes in blood flow. The events leading up to and following preterm birth can affect the blood flow causing the vessels to break and bleed. If these vessels rupture, bleeding occurs in or near the ventricles, the blood initially accumulates in the germinal matrix and may spill into the neighbouring ventricle.

(Perlman, 1998)

Risk Factors

As is similar with other complications of preterm birth, the younger, smaller, and sicker preemie baby is more likely to have an intraventricular or germinal matrix hemorrhage. Another factor that can place a baby at risk for IVH is related to the heart. The persistence of patent ductus arteriosus (PDA) can alter brain blood flow and circulation considerably. Patent ductus arteriosus can cause increased stress on an already immature respiratory system and can lead to a relative reduction in brain blood flow. If the ductus in then closed, either naturally, pharmacologically, or surgically after several days, there can be an increase in cerebral blood flow. These changes or fluctuations in blood flow can result in bleeding within the germinal matrix.

(Evans & Kluckow, 1996))

Diagnosis and grading systems

Bleeding which causes a germinal matrix or intraventricular haemorrhage is most likely to occur on the first day of life and 90% take place during the first 3 days. If a preterm baby does not have a bleed of this kind by the end of the first week it is very unlikely he/she will ever have one.

Preemies that are at risk of bleeding within the brain are routinely given head ultrasounds. (There are a number of grading systems in place describing the severity of IVH. We will describe just one of those here.

• Grade 1 IVH refers to small bleeds in the subependymal germinal matrix
• Grades 2 and 3 IVH refer to extension of blood into the ventricular system, filling either < 50% of the system (grade 2) or more than 50% and usually accompanied by ventricular dilatation (grade 3).
• Grade 4 IVH is not actually intraventricular hemorrhage at all, but rather refers to the periventricular hemorrhagic venous infarction that occurs with obstruction of blood flow through the periventricular terminal vein. This means a haemorrhage outside the ventricles, in the white matter of the brain.

Incidence

The incidence of IVH can vary between studies but it related to degree of prematurity, with those infants born earliest being at greatest risk. Overall rates of IVH are 20 to 25%. Low grade IVH is considered benign, in that these infants exhibit similar long-term outcome to those without IVH, however high grade IVH is related to quite poor outcome including motor and cognitive impairment, especially those with white matter infarction.

Of those preterm babies who develop an IVH most will be mild bleeds;

• 40% grade 1,
• 30% grade 2,
• 20% grade 3, and
• 10% grade 4.

Preemies born less than 1,000 g (2 pounds) or less than 28 weeks – 50% to 60% chance of developing IVH

Preemies born less than 1,500 g (3 pounds 3 oz.) – 10% to 20% chance of developing IVH

(Sherlock, Anderson, & Doyle, 2005) (Papile, Burstein, Burstein, & Koffler, 1978)(Horbar, Badger, Carpenter, & Fanaroff, 2002)(Inder & Volpe, 2000; Volpe, 2001b)

Hydrocephalus

Hydrocephalus is also called “water on the brain” which means there is an abnormal amount of cerebrospinal fluid in the brain and brain ventricles. Following an intraventricular haemorrhage the blood clots can block the drainage system of the brain or scar the brain membranes. This can result in increased pressure inside the skull and enlargement of the head.

Incidence

65% to 100% of preterm infants with a grade 4 intraventricular haemorrhage (depending on its location) suffer from hydrocephalus

Approximately 25% of preterm infants with grade 3 intraventricular haemorrhage suffer from hydrocephalus.

(Inder & Volpe, 2000; Inder, Wells, Mogridge, Spencer, & Volpe, 2003; Zaichkin, 2009)

Cystic Periventricular Leukomalacia

Periventricular Leukomalacia is when the white matter of the brain is injured near the ventricles. There are many fibres in the brain that carry messages between the brain and the nerves in the spinal cord. The fibres are prone to injury from lack of blood flow or oxygen, especially during vulnerable times during development.

The injury from PVL may have occurred due to events close to the birth, however PVL may not appear on imaging for several weeks after birth.

Cystic PVL is the most severe form of white matter injury and is thought to occur as a result of hypoxia-ischaemia and/or infection. The lesions can occur on both sides of the brain and in severe cases may extend from the back of the brain (occipital lobe) to frontal regions of the brain. Cystic PVL also runs a high risk for cerebral palsy and other developmental difficulties.

(Inder, et al., 2003; Volpe, 2001a)

Incidence

Cystic PVL is relatively uncommon, affecting approximately 3-5% of surviving very preterm infants.

(Inder, et al., 2003)

 

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Technical Reference List

Evans, N., & Kluckow, M. (1996). Early ductal shunting and intraventricular haemorrhage in ventilated preterm infants. Archives of Disease in Childhood, 75(3), F183-F186.
Inder, T. E., & Volpe, J. J. (2000). Mechanisms of perinatal brain injury. Semin Neonatol, 5(1), 3-16.
Inder, T. E., Wells, S. J., Mogridge, N. B., Spencer, C., & Volpe, J. J. (2003). Defining the nature of the cerebral abnormalities in the premature infant: a qualitative magnetic resonance imaging study. J Pediatr, 143(2), 171-179.
Perlman, J. M. (1998). White matter injury in the preterm infant: an important determination of abnormal neurodevelopment outcome. Early Human Development, 53(2), 99-120.
Volpe, J. J. (2001a). Neurobiology of periventricular leukomalacia in the premature infant. Pediatr Res, 50(5), 553-562.
Volpe, J. J. (2001b). Perinatal brain injury: From pathogenesis to neuroprotection. Mental Retardation and Developmental Disabilities Research Reviews, 7(1), 56-64.
Zaichkin, J. (2009). Newborn Intensive Care: what every parent needs to know (3rd ed.). MI: Sheridan Books.

 

 

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