Wed, May 07, 2014 - Page 9 News List

‘Shaken baby syndrome’ prosecutions uncertain, ‘speculation’

By Waney Squier

The most tragic event that can befall new parents is the sudden, unexpected death of their baby. Perhaps the only thing worse is the parents being wrongly accused of causing the death and prosecuted for it, owing to the medical community’s misinterpretation of the findings.

A small number of babies who collapse and die unexpectedly in their first year are found to have one or more of the following three symptoms in common: bleeding just outside the brain (subdural hemorrhage), bleeding at the back of the eye (retinal hemorrhage) and brain swelling.

These same features are also seen in some babies who have suffered trauma, such as falls or motor vehicle accidents. Yet many babies with these symptoms have no history or medical evidence of trauma (such as fractures, abrasions or bruises) physical abuse or neglect.

Pediatricians wrestled with this conundrum until the 1970s, when it was proposed that shaking might induce rotational forces and cause the “triad” of symptoms without bruises or fractures. Over the years, these findings evolved into “shaken baby syndrome” (SBS), a medico-legal hypothesis that remains contentious and scientifically unproved to this day.

The SBS hypothesis attributed the triad of symptoms to the physical rupture of blood vessels on the brain’s surface and in the retina, as well as the tearing of nerve fibers within the brain. It was suggested that these outcomes required a force equivalent to a multistory fall or major motor vehicle accident, causing immediate symptoms or collapse. Because violent shaking cannot be accidental, the hypothesis simultaneously established a criminal act and identified the perpetrator, typically the person with the baby at the time of collapse.

Although the SBS hypothesis was incorporated into medical training and judicial decisions worldwide, it remained untested for almost two decades.

In 1987, the first biomechanical experiments found that the force of shaking is much less than that of impact and concluded that shaking alone was unlikely to cause the triad of symptoms.

Subsequent research in my specialty, pediatric neuropathology, established that the medical basis for the SBS hypothesis is also flawed. We learned that the brain damage in these children did not reflect trauma to nerve fibers, but rather a failure of blood supply. We also learned that the typical subdural hemorrhages in these cases are too thin to result from the rupture of the large bridging veins on the brain’s surface and that the same findings are seen in natural deaths. In the past decade, the list of other causes — including accidental trauma, congenital causes and natural illness — has continued to grow.

Perhaps the most compelling observation in recent years is that subdural hemorrhages are present in nearly half of normal, healthy newborns with no evidence of birth trauma. These findings, combined with the immature anatomy of the infant dura, suggest that dural bleeding in young babies may be a natural protective device; a reservoir to prevent backflow into the brain’s blood vessels during the pressure fluctuations of normal labor and delivery.

Because these anatomical features persist into early childhood, the dura may remain similarly vulnerable to bleeding beyond the newborn period. Birth-related bleeds and those attributed to shaking are most often located in the folds of membranes covering the brain, which have more and larger blood vessels at that age than later in life.

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