SBS 101

"Shaken Baby Syndrome"
A Tutorial and Review of the Literature

The standard diagnosis/charge of "Shaken Baby Syndrome" (SBS) occurs when a child is admitted to an emergency room with 1) subdural hematomas, 2) retinal hemorrhages, and 3) a history other than that of a motor vehicle accident or a fall from an appreciable height. Some have referred to this as the "Shaken Baby Triad." The original theory of the American Academy of Pediatrics and most Children's Hospitals across the nation was that these signs and symptoms were exclusively found in nonaccidental trauma. However, evidence based research on childhood subdurals has shown that there are multiple disorders or accidental injuries which mimic the symptoms once thought to be exclusively those of "Shaken Baby Syndrome." This tutorial looks at the research surrounding childhood head trauma and our ability to differentiate between nonaccidental trauma and alternate explanations.

Subdural Hematoma: is a collection of blood that pools under the dura. The dura is a relatively tough connective tissue (collagenous) membrane, about the thickness of parchment paper. It is firmly attached to the under surface of the skull, and in the spinal canal, it is separated from the bony structure by a layer of fatty tissue. The inner underside of the dura is applied to a much thinner, transparent membrane, the arachnoid, which overlies the brain and subarachnoid space. This interface is easily separated, forming the subdural space. The subdural space is referred to as a "potential space" because a space is not generally created unless a subdural hematoma or another space occupying mass is formed.

When a subdural hematoma forms, it is generally an indicator of a broken vein on the underlying surface of the brain. Veins draining the surface of the brain pass through the subarachnoid space and then the dura on their way into the sagittal sinus and other intradural venous sinuses that carry the venous blood eventually to the jugular system. If one or more of these veins that "bridge" the dura are injured, bleeding occurs into the subdural "space," causing a subdural hematoma (clot). For whatever reason, most subdural hematomas in "Shaken Baby" cases, as well as nonaccidental trauma cases in infants, are bilateral. An early study by Gulthkelch found that subdural hematomas were bilateral in children 78% of the time. This differs from the rates found in adults. A study by Nashelsky found bilateral subdural hematomas in only 50% of adult cases.

Contra Coup Injuries: Contra Coup injuries occur when there is an injury to the opposite side of the head from the impact site. Contra coup injuries are generally thought to be an indicator of a moving head hitting a stationary, unyielding force or object (Spitz and Fisher III ed.).

Retinal Hemorrhages: are small hemorrhages on the back of the eye. The presence or absence of retinal hemorrhages and/or its characteristics is often used by prosecution doctors to determine whether or not the case is nonaccidental trauma. This is not an accurate mechanism. The pattern, number, location or type of retinal hemorrhages that "point to a diagnosis of SBS" or other nonaccidental trauma has changed many times. The mechanism(s) behind retinal hemorrhages in infancy were never fully explained by proponents of "SBS." Current research now points to a mechanism involving rapid increases in intracranial pressure, cerebral venous spasm or increased venous pressure, and possibly hypoxia. Most studies do not support a mechanical etiology. Sometimes, the retinal hemorrhages are accompanied by nerve sheath damage or bleeding in the subdural space of the optic nerve. This finding has been considered an indicator of a greater degree of damage. 

Skull Fractures

The classic interpretation of infantile skull fractures is that anything other than a non-widely spaced simple linear fracture of the parietal bone is the result of nonaccidental injury (Kravitz, et. al.). Such fractures would include depressed, stellate, comminuted or other complex types of skull fractures. Many believe that falls of less than 3 feet only rarely produce any kind of skull fracture, and that skull fractures only occur when extremely violent forces are brought to bear on the infant. Others (Weber, Plunkett) have demonstrated that simple as well as complex fractures of the skull can occur from "short" falls. Skull fractures do not necessarily cause signs or symptoms, and may not be associated with underlying dural or brain injury (Shutzman and Greenes). Very young infants (<6 months) may have major cranial deformation due to an impact but no skull fracture, because their skulls are malleable and elastic, whereas older children have more rigid adult-like ossified skulls and are more vulnerable to skull fractures. The fracture threshold for an infant is approximately 10% that of a child or adult (Goldsmith - personal communication, Marguiles and Thibault). A special pattern of bilateral skull fracture can occur when there are crushing forces applied against the infant skull. Skull fractures cannot occur without impact of the head against a rigid object. They cannot occur with shaking.

Skull fractures are caused by a deformation of the skull due to impact of some kind. The likelihood that a child will suffer a skull fracture depends on the force, location of the impact, age of the child and biologic/mechanic characteristics/properties of the skull at the point of impact. Children with open sutures and more flexible skulls are not as likely to fracture in short falls as are older children with fully developed enclosed skulls.

Simple Linear Fractures: These are fractures that follow one linear pattern.

Multiple Fractures, Complex Fractures or Fractures: These fractures are said to require a greater degree of force. Skull Fractures from a fall to a flat surface generally show an impact site with one or several fracture lines radiating from the point of impact, whereas falls to raised surfaces, or blunt impact with an object can show depressed fractures.

Depressed Fractures or Fractures with a "Punch Out": These are fractures in which bone fragments are pushed inward (looks like a hole punched out) and are generally thought to be seen when a person falls on a sharp corner or on a flat surface with a raised object on it (rock on a tile floor or barrette on a child's head). These types of fractures are also seen with blunt force trauma (hammer to the head) or missile trauma (gunshot wound). However, a depressed fracture may also be found with an impact to a flat surface.

Compound Depressed Fractures: These are fractures with multiple lines and a larger bone fragments depressed inward from the skull cavity. They are generally seen with blunt force trauma and falls to surfaces with raised edges or objects. These types of fractures generally require medical intervention and/or surgery to prevent serious brain damage or disorder.

Temporal Bone Fractures

Longitudinal: These are front to back skull fractures of the skull thought to be caused by blunt force trauma to the head around the face, frontal or occipital regions. They can also be caused by compression of the head from front to back.

Transverse Fracture: These are side to side fractures of the skull caused by impact or compression to the sides of the head.

Skeletal Fractures

Rib Fractures: Rib fractures in children are generally thought to be the result of some mechanism of compression to the chest cavity. Rib fractures are said to be "classic indicators" of Shaken Baby Syndrome. However, less than 10% of the cases charged as SBS show evidence of rib fractures. The issue of rib fractures in infants who have received CPR (especially by untrained hands) has not been thoroughly explored.

Metaphaseal Fractures: These are fractures of the long bones (arms and legs) caused by twisting, pulling, jerking or wringing of a child's arms or legs. These types of fractures are most often found in children under 1 year old. These fractures are said to be suspicious of child abuse.

Osteogenisis Imperfecta or "Brittle Bone Disease": This is a genetic disease seen mostly in newborn babies and children caused by a collagen disorder which causes kids to have increased susceptibility to fractures. True OI is a permanent condition and is based on a faulty type or lack of collagen in the bones. However, fractures generally decrease after hormonal changes in adulthood.

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