All premature babies with a suspected brain problem will receive a head ultrasound, as well as several other assessments such as further imaging, electroencephalograms and evoked potentials.
Measuring the brain and brain function
All premature babies will have their head circumference measured. Head circumference can be significant for premature babies for several reasons. First, an abnormally enlarged head could be an indication for intraventricular hemorrhage — bleeding into cavities called ventricles in the brain - or other problems with the brain. Quickly knowing whether this is the case or not is important in that, if detected early, the possible damage that comes as a result of some of these conditions might be minimized. Second, immediately measuring the head will give a base measurement that will give an indication of how quickly the premature baby’s brain is growing. This may become important in the coming months; head circumference can often give an indication of whether the premature baby has some type of neurological impairment.
That being said, an abnormal head circumference is not sufficient to diagnose brain problems. All premature babies with a suspected brain problem will receive a head ultrasound.
Despite all the tests that may be done on a premature baby’s brain and behaviour, it is often months before any impairment can be detected. For example, Extremely and moderately premature babies are often given head ultrasounds. Soon after birth, this imaging test may show nothing; however, months later, impairments may emerge.
Premature babies are also tested for mobility and flexibility problems, which can be signs of brain impairments. However, like a head ultrasound, these tests often do not indicate anything until they are repeated months later.
Brain imaging and evoked potentials
All premature babies with suspected or confirmed brain injuries will undergo some form of imaging to assess the amount of damage. Additionally, assessments of brain activity will also be performed. These tests are done to assess and monitor the amount of actual damage to the brain at a particular site, and to assess the impact that damage has made on brain activity as a whole. With this information, staff in the Neonatal Intensive Care Unit (NICU) will attempt to determine if there are immediate treatment options, and predict the long-term result of such an injury. These assessments may be performed on a regular and ongoing basis.
For example, a premature baby with white matter damage, a type of injury to the brain tissue, will be imaged to determine the size and location of the damage. they will also be assessed to determine how the damage may be affecting the organization of electrical activity in the brain as a whole. Using all this knowledge, the doctors may be able to give an indication of how the baby will be affected as they grow older. They may be able to estimate how much cognitive functioning and body movement will be affected by the injury in the long run. This information will also give an indication as to the types and frequency of therapy that will maximize the baby’s future abilities.
Imaging
There are three main types of brain imaging that are currently available. These are:
- head ultrasound (HUS), which uses sound waves to create a visual image of the brain
- computed tomography (CT) scan, which uses an X-ray and a computer to take cross-sectional pictures of the head
- magnetic resonance imaging (MRI), which uses the signature vibrations of hydrogen atoms within each cell to create cross-sectional pictures of the head. A magnet, radio signals, and computer are used to create the pictures.
The use of imaging as a predictor for future motor and cognitive abilities is fairly imprecise and MRI in premature babies is a relatively new diagnostic tool. It is a picture only and there is much about the brain function that is not well understood as it relates to the structure, site, and extent of injury. It is known that, under certain circumstances regarding the location and extent of the injury, the brain can adapt to the point where satisfactory brain function returns; however, it is difficult to determine the cases in which this will occur. More frequently, brain injury will have occurred but is not recognized on routine scanning. Some effect on the body, mind, or both is seen in later assessments; again, determining what type of effect, and to what extent, early on in the NICU course, can only be estimated at this point. Studies are underway in an effort to make more precise predictions of future abilities based on better imaging of brain injury and better assessments of brain function.
Electroencephalograms and brain activity
There are several ways to assess brain activity, some of which may be familiar to parents since these tests are also conducted on adults. In general, these tests measure the amount of electrical activity in the brain or in specific parts of the brain.
An amplitude-integrated electroencephalogram (αEEG), also called a cerebral function monitor (CFM), provides quick, general information about a baby’s brain activity by measuring background electrical activity in the brain. Using three small wires, called leads, attached to the head, the aEEG indicates the generalized level of electrical activity occurring across the brain. Electrical activity is recorded and then represented on printed paper as wavy lines which doctors can interpret. An αEEG is also a valuable detection tool for newborn babies experiencing certain types of seizures as well as brain injury.
Doctors use the aEEG to see where the premature baby has problems with the electricity made in the brain cells. The wavy lines that the electricity patterns make change when there is a problem, such as a seizure. The pattern of wavy lines helps the doctor see what and where the problem is, and how to best treat the problem.
It should be noted that accurate readings from an aEEG can be compromised by mechanical ventilation and by a baby’s inability to remain still during the test.
Evoked potentials
Evoked potentials can be a predictor for body and/or cognitive disabilities stemming from brain injury. Evoked potentials differ from EEGs in that they measure brain activity when specific stimuli are given to the premature baby. Typically, these stimulations can be visual, auditory, or tactile. To put it another way, the baby’s brain activity is measured while they are subjected to sights, sounds, or touch. More specifically, evoked potentials measure if the brain responds to the stimulus and the time it takes for the brain to respond to the stimulus. In a way, this is a measurement of how long electrical signals take to go from one part of the brain to another. Science has a very good idea of how long this response takes in an uninjured brain; therefore, response times of the injured brain can be compared with the known response times for the healthy brain. The difference in the time the response takes can give an idea of how much a brain injury is affecting brain function. These tests last about 45 minutes and are usually easy to perform, though they may require mild sedation of some kind.
Visual evoked potentials (VEPs) measure the brain’s response to light. Using three small electrodes with wires attached to a computer, we can pick up the brain’s response to a flashing red light stimulus from a light emitting diode goggle placed gently over the baby’s eyes. The light causes large amplitude simple wave electrical impulses to be generated by the cells in the occipital cortex at the back of the brain. When these impulses are absent in the occipital cortex, it implies that very important damage to this part of the brain has occurred.
Auditory evoked potentials (AEPs) measure the brain’s response to sound. These tests are different from hearing tests or brain stem evoked response audiometry (BERAs) in that they demonstrate the presence or absence of the pathway in response to a very loud 90-decibel click or noise. A wave form consisting of five major peaks is generated by different cells along the path at different points in the inner ear, the brain stem, and sensory cortex of the temporal lobe. Some or all of the waves may be missing in brain damage. The impulses are again picked up by three simple wires applied to the scalp and using a computer to amplify and integrate the waves so that the random activity is cancelled out and the wave resulting from the sound may be seen.
Somatosensory evoked potentials (SEPs) measure the brain’s response to touch. The stimulus is experienced in the premotor sensory cortex of the brain and an intact response implies that that part of the brain has been spared when an insult occurred. Using a similar set of three electrodes, we capture the electrical waves generated by the stimulus, amplify them, average out all the background noise and display them on the computer screen. These waves are very sensitive to insult and so, if they remain intact, it suggests that the injury has been very mild and localized, probably with no long-term motor or cognitive impact.