Shaken baby syndrome can occur from as little as 5 seconds of shaking. Injuries are most likely to happen when there is both acceleration (from shaking) and deceleration (from the head hitting something). Even hitting a soft object, such as a mattress or pillow, may be enough to injure newborns and small infants. The result is a type of whiplash, similar to that seen in some auto accidents. A number of factors make infants highly vulnerable to whiplash forces. For example, their brains are softer, their neck muscles and ligaments are weak and not fully developed, and their heads are large and heavy in proportion to their bodies. When an infant or toddler is shaken, the brain rebounds against the skull. This can cause bruising of the brain (cerebral contusion), swelling, pressure, and bleeding in the brain (intracerebral hemorrhage). The large veins along the outside of the brain may tear, leading to further bleeding, swelling, and increased pressure (subdural hematoma). This can easily cause permanent brain damage or death. Shaking an infant or small child may cause other injuries, such as damage to the neck, spine, and eyes. Eye damage is very common and may result in loss of vision (retinal hemorrhage).
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