the fontanelles (otherwise known as “soft spots”). The skull does not fully fuse and harden until around two years of age. One problem of the pliable infant skull is that it lacks protection from impact. A hard hit can more easily transmit harmful forces deeper within the brain than an adult skull.
The next layer of the brain is the dural membrane—a tough, durable membrane that covers the entire brain. It is formally called the dura mater and is attached to the skull. It moves separately from the brain and can tear underlying veins and nerves. Any bleeding underneath is called subdural (below the dura). Any bleeding above it is called epidural (outside the dura). These terms are important in the upcoming discussions on falls and head injuries.
Deeper within the brain’s layers is the arachnoid membrane, which is a thin, web-like layer that loosely attaches to the layer below it. There is a space underneath the arachnoid, which is called the subarachnoid space. This space allows cerebrospinal fluid to flow within the spinal column and the brain. Brain injury can cause bleeding within this space and is called a subarachnoid hemorrhage.
The final layer, the pia mater, adheres to the convexities (ridges) of the brain and is impermeable to fluid. It protects and cushions the brain.
The brain itself is made of gray and white matter, each serving its own function for movement and autonomic processes. The color difference arises mainly from the whiteness of myelin in white matter and the grayness of capillaries and neurons in gray matter. These matters are separate entities and shear off each other during violent shaking. Gray and white matter can also be torn more easily in infants and young children due to the softness of the brain. On a normal CT/MRI scan, the infant brain is clearly defined and symmetrical, with a clear differentiation of gray matter and white matter. Brain swelling from trauma (edema) diminishes or obliterates this difference and on a diagnostic scan appears as a patchy covering over the brain (hypodensity). Cohen and associates coined the term “reversal sign” to describe a state in which severe edema and tissue destruction makes the white matter of the brainstem, thalamus and cerebellum appear more dense than the surrounding gray matter portions of the brain.2 This irreversible brain damage has also been termed “the black brain.”3
Throughout the layers of the brain, blood vessels weave and are loosely attached. During a shaking event, these immature blood vessels can stretch and tear, causing bleeding within the membranes of the brain—most typically subdural bleeding. Multiple broken blood vessels seep fresh (or acute) blood into localized areas or spread over a wide area of the brain. Over a period of hours or days a clot will form, which is congealed subdural blood. The clot is called a hematoma. This clot expands and presses on the brain and physical symptoms will appear in an infant or child such as vomiting, lethargy, poor sucking ability, chirping cries, etc.
DIFFUSE AXONAL INJURY
The billions of nerve fibers that are within the brain can also be dramatically affected. These nerves are rapidly growing in infants and young children and violent shaking can stretch and tear these fibers, similar to how this motion affects blood vessels. Specific neurons, called axonal nerves, communicate with each other, sending messages that “teach” developmental information within the brain. Research has found that rotational forces and sudden deceleration movements (like in a motor vehicle accident or a shaking episode) cause axonal nerves throughout a large section of the brain (typically where the grey and white matter of the brain intersect) to be disrupted and break. This is known as diffuse axonal injury (DAI). Unfortunately, there is no cure when DAI occurs. Once an axon is broken, it remains broken. Most often, it is diagnosed microscopically—especially during an autopsy. DAI is the reason many infants fail to develop normally. The nerves that are in place to learn an activity are broken and stay that way. Mental handicaps and cerebral palsy are two examples of the aftereffects of shaking. These conditions in a baby are permanent lifetime consequences. They are also signs of brain damage, with a wasteland of previously healthy axons that can never be repaired. DAI is a very rare cause of death; instead, other consequences of brain trauma are the cause—oxygen deprivation, edema, etc.
When an infant is shaken to the point of causing physical harm, he or she will lose consciousness immediately. The brain is overwhelmed by the traumatic event and, like any head injury, shuts down quickly. Since infants and young children are unable to communicate their symptoms, parents and other caregivers may mistake excessive sleeping or irritability for normal behavior. Even when an infant is taken to a doctor, symptoms may be mistaken as the flu or another type of illness. Head injuries may not be suspected, so the infant is allowed to go home, where further complications may occur (or even further abuse).4
SUBDURAL BLEEDING
A subdural hematoma is a blood clot formed from an accidental, natural or abusive cause. Subdurals are the foundation for a diagnosis of Shaken Baby Syndrome and are typically bilateral (both sides). Subdurals are formed from rotational forces that occur when a child is shaken. In terms of physics, research has shown that the types of subdural hemorrhages that are seen in SBS involve a rotation of the brain that pulls and snaps the fragile bridging veins that cross the young child’s brain. This is the action that causes the blood to spread and pool on the brain’s surface. A rotational subdural is more likely to occur during severe shaking than a contact subdural, which will be described next.
CT and MRI scans can identify blood and injury with accuracy. Blood shows as a white highlight on scans, which is also called acute blood (also known as hyperdense). There may be older blood present which sometimes is called hypodense—appearing more grayish. Once doctors identify the location and size of subdural bleeding or bleeding in other locations of the brain, then surgery is typically performed to clear the blood. If the size of the subdural is small, surgery may not be necessary, since the subdural blood will naturally be resorbed by the brain.
Another way that a subdural hemorrhage can occur is from a blow to the head or a direct impact. In this instance, it is known as a “contact subdural.” The mechanism for this to occur is often a fall onto a hard surface. Physics is brought into play here as well. The type of motion for a contact subdural is called a translational fall—from point A to point B in a straight line. When an infant or young child falls from an elevated surface and his or her head impacts a hard surface, a fracture may or may not occur. Beneath that fracture, a contact subdural may develop. The bleeding, especially in accidental falls, is typically epidural and necessitates immediate removal of the blood. Subdural bleeding in translational falls can be mass-occupying, meaning the hematoma expands and presses downward on the brain. Such bleeding needs surgical evacuation.
When an infant falls from an elevated surface down to a carpeted or hard floor, the chance of significant damage to the head is small. The greater the height (i.e. from a parent’s arms), the greater the potential for head injury.
If an infant was playing in a walker and happened to roll downstairs while he or she was still inside, then that would be a rotational event, where possible subdural bleeding occurs. There is the physical manifestation of acceleration/deceleration in rotational falls (similar to motor vehicle accidents) and bleeding in any rotational fall can be bilateral.
An interhemispheric subdural hemorrhage is very specific to shaken baby cases, as the blood actually cleaves between the hemispheres. Because of the whipping motion during shaking, blood goes right up the middle—between the left and right hemisphere of the brain. Interhemispheric bleeding is seen in the posterior (or back) section of the brain. In 1978, Dr. Robert A. Zimmerman first correlated interhemispheric subdurals with violent shaking.5 It is also not a good finding prognosis-wise, since subsequent CT scans of Zimmerman’s patients found that 100 percent had cerebral atrophy (brain shrinking).
EYE INJURIES
According to Dr. Alex Levin, “The overwhelming body of literature supports a conclusion that severe hemorrhagic retinopathy in otherwise previously well children without obvious history to the contrary (e.g. fatal head crush) suggests that the child has been submitted