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Abusive head trauma (AHT) or shaken baby syndrome is a type of inflicted traumatic brain injury that is a preventable and severe form of physical child abuse (CDC, nda). The child has inflicted upon her or him, severe repetitive acceleration-deceleration forces with or without blunt impact to the head that result in a characteristic pattern of injuries (Case & NCSBS, nde). This typically occurs through the violent shaking an infant by the shoulders, arms, or legs (CDC,nda; NINDS, 2010). AHT can occur from as little as 5 seconds of shaking (NIH, 2009). AHT leads to a brain injury, which is much like an adult may sustain in repeated car crashes (CDC,ndb).
Infants are believed to be particularly susceptible to AHT because of their relatively large and heavy head, making up about 25% of their total body weight, undeveloped neck muscles, and small size (NCSBS, nd). The infant’s neck muscles are too weak to support such a disproportionately large head. Shaking the child while holding the child about the chest allows for substantial rotational shearing forces to be generated, as well as the bouncing back and forth of the brain against the skull causing a range of brain injuries (NINDS, 2010; Salehi-Had, et al., 2006). This can cause bruising of the brain (cerebral contusion), swelling, pressure, and bleeding in the brain. The large veins along the outside of the brain may tear, leading to further bleeding, swelling, and increased pressure. This can easily cause permanent brain damage or death (NIH, 2009).
The actual injury that occurs in the brain is traumatic diffuse axonal injury. This is caused by the movement of the brain within the skull in response to the acceleration-deceleration movement of the head that occurs in shaking. This abrupt rotational movement of skull results in tears of the axonal processes of nerve cells and tears to small blood vessels. Rarely are there actual tissue tears in the brain. The portions of the brain that are impacted are those beginning from the brain’s surface and then moving deeper within the brain. Axonal tears are difficult to see in young children due to the small size of the axonal processes (Case, NCSBS, nde).
Reece (NCSBS, ndf) describes the trauma:
“During such assaults, the bridging veins running from the surface of the brain to the superior sagittal sinus, rupture and bleed into the subdural and/or subarachnoid spaces. Direct traumatic damage occurs to the brain; hypoxia during and after the assault causes further irreversible damage to brain tissue; and the cascade of injury continues as there is breakdown of dying brain cells that release intra-cellular enzymes, injuring adjacent neurons. The combined effect is destruction of brain tissue, leading to cerebral edema, raised intra-cranial pressure within the closed skull of the infant, decreased blood flow to the brain and a vicious circle of anoxia, cerebral edema, and death of brain tissue. These insults to the brain cause the signs, symptoms, radiologic and laboratory findings that characterize the course of this form of inflicted brain injury.”
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