Abusive head trauma, also known as shaken baby syndrome or shaken impact syndrome, is a form of trauma that arises when a baby (or small child) is shaken and/or struck so violently that it leads to cerebral injury. Inconsolable crying is usually the trigger for such actions on the part of the caregiver. Victims are typically between 2 and 8 months of age, although this type of injury has been seen in children up to 4 years old. The National Center on Shaken Baby Syndrome has estimated that in the US, 600 to 1,400 children annually are injured or killed by shaking. The actual figure may be greater. All races/ethnicities and levels of socioeconomic status are affected, but physicians are less likely to recognize abusive head injury when the caregivers are white and from a higher socioeconomic class, and when the child comes from an intact family.
It is thought that the primary injury arises as a result of the multidirectional forces from shaking, leading to a form of whiplash injury associated with diffuse axonal injury, tearing of bridging veins, and subsequent intracranial bleeding. The secondary brain injury is due to a combination of hypoxia, ischemia, and brain edema. The end result is destruction of brain cells, a reduced supply of oxygen to brain cells, and brain swelling leading to varying degrees of neurological deterioration and occasionally death. Anatomically, the combination of a not-yet myelinated brain, a heavy-set head upon weak neck muscles, and lack of control of the head and neck are factors that predispose babies to this form of injury.
Often no history of trauma is offered, or there is a history of a short fall or a history that a sibling injured the infant. The degree of injury is not compatible with the history given.
Shaken baby syndrome is characterized by a triad of clinical features: subdural hemorrhage, retinal hemorrhage, and encephalopathy. Retinal hemorrhages are present in approximately 85% of cases and may be unilateral, but the diagnosis of abusive head trauma should not be excluded if they are absent.
The degree of damage inflicted depends on the force of shaking and the length of time the baby was shaken. On presentation, the baby may appear to be lethargic, irritable, or in a comatose state; have bulging fontanels; be bradycardic and hypothermic; and seem to have difficulty breathing.
Symptoms of shaken baby syndrome may be nonspecific and include:
Brief resolved unexplained event (BRUE)
Difficulty breathing / apnea, which may be severe enough to require intubation
Loss of consciousness / comatose state
Rigidity / hypertonia
Inability to lift the head / hypotonia
Size of head appears larger than usual if there have been prior episodes
In many instances, no external injuries are apparent, but a thorough head-to-toe physical exam should be carried out. Eye examination by an ophthalmologist is important if this diagnosis is suspected. Bilateral retinal hemorrhages (and sometimes unilateral) are a classic finding. Skeletal survey (series of 20 radiographs) may reveal the presence of rib or classic metaphyseal lesions. However, fractures in the acute phase may not be visible until 2 weeks later.
Following episodes of infant shaking, the consequences can vary from no detectable adverse effects to death. The fatality rate following this type of trauma is high, at approximately 20%, and the prognosis for those that survive is variable. Even when infants survive, there remains the possibility of lifelong disabilities that include cerebral palsy, intellectual disability, blindness, paralysis, epilepsy, speech delay, hearing impairment, and learning disabilities.
Notably, this pattern of injury characterized by retinal hemorrhage, subdural hemorrhage, and encephalopathy has not been shown to arise from accidental falls from short heights (<5 meters). Neither has it been associated with playfully throwing a baby into the air and catching the baby.