Patterns of presentation of the shaken baby syndrome

Editor—One of the controversies that has recently arisen in cases of alleged shaken baby syndrome concerns the disparity between certain neuropathological findings at necropsy and whether these findings are consistent with the entity regarded as the shaken baby syndrome.

A database was collected for more than five years of documented Scottish cases of suspected non-accidental head injury diagnosed after a multiagency assessment and including cases with uncoerced confessions of perpetrators and criminal convictions. Several patterns of presentation allow delineation of cases into four predominant types.

Hyperacute encephalopathy (cervicomedullary syndrome)

This hyperacute encephalopathy (6% of all cases) results from extreme “whiplashing” forces, the infant suffering the equivalent of a broken neck or, more correctly, a broken brain stem. In infants with a median survival of one day Geddes et al described localised axonal damage at the craniocervical junction, in the corticospinal tracts, and in the cervical cord roots, consistent with hyperflexion and hyperextension movements.¹ These cases, which truly reflect a “whiplash” shaking injury to the stem, are infrequently seen by clinicians because the patients are either dead on admission or die shortly thereafter.

Presentation is at 2-3 months of age, with acute respiratory failure (direct medullary trauma) and cerebral oedema (a “black brain” on imaging). At necropsy these infants have severe brain swelling and hypoxic injury but little axonal shearing and only a thin (trivial) subdural haemorrhage. Such presentations could result from a primary injury to the brain stem, induced by hyperflexion and hyperextension, or, rarely, from traumatic thrombosis of the vertebral arteries in the foramina of the cervical vertebrae.

Acute encephalopathy

An acute encephalopathic presentation (53% of cases) is characterised by a depressed conscious state, raised intracranial pressure, fits, apnoea, hypotonia or decerebration, anaemia, shock, bilateral subdural haematomas, and widespread haemorrhagic retinopathy. Coexistent rib fractures, metaphyseal fractures, or other non-accidental injuries may be found. This is the commonest presentation seen by paediatricians and is referred to as the classic shaken baby syndrome (repetitive rotational injury). Depending on whether additional signs of impact are noted (focal subdural, extradural, or subgaleal haemorrhage; scalp injury; or skull fracture), the syndrome has been referred to as the shaken impact syndrome.

The brain injury is well documented from studies of magnetic resonance imaging,² which show widespread vascular shearing with convexity subdural haemorrhages enlarging over the first week (as well as interhemispheric, subtemporal, suboccipital, and posterior fossa subdural haemorrhages), torn bridging veins, cerebral oedema, haemorrhagic contusions and lacerations, and white matter shearing, with tears and petechial haemorrhages at the junction between grey and white matter and in the corpus callosum. Up to 60% of cases have serious long term morbidity.

Subacute non-encephalopathic presentation

In infants with a non-encephalopathic subacute presentation (19% of cases) the brain injury is less intense, without swelling, diffuse cerebral hypodensities, or clinical encephalopathic features. These children have various combinations of subdural and retinal haemorrhages, rib fractures and other skeletal fractures, bruising, etc. The outcome in this group is better.

Chronic extracerebral presentation

A chronic extracerebral presentation (22% of cases) is seen in children of a few months of age who present with an isolated subdural haemorrhage, which is often chronic (> 3 weeks) and late in presenting. A rapidly expanding head circumference and signs of raised intracranial tension are common: the child may be irritable, vomiting, failing to thrive, hypotonic, fitting but with little encephalopathy.

The primary injury is extracerebral but with potential secondary injury from raised intracranial pressure and reduced cerebral perfusion pressure and hypoperfusion, oedema, and metabolism to flow mismatch in the white matter.³ Any retinal haemorrhages originally present have disappeared by presentation. The injury has occurred weeks earlier, and its force has been sufficient to rupture the weakest bridging vein(s) but insufficient to produce an acute encephalopathy. The prognosis is good with recognition and appropriate treatment.

Clinicians will have difficulty in attributing a causative mechanism and timing to such late presenting (idiopathic) subdural haemorrhages. Only in the presence of residual features of physical abuse (such as fractures), along with identifiable risk factors, would non-accidental injury be considered. Most cases remain aetiologically unexplained, although trauma remains the likely cause, but they are unlikely to be legally pursued beyond medical investigations and social work inquiry.

Conclusions

We postulate that a spectrum of clinical features is related to the intensity and type of injury in babies with inflicted brain injury, reconciling the clinical and neuropathological findings. Infants can be traumatically injured in many ways, and many instances are unwitnessed. Thus the generic term non-accidental head injury or inflicted traumatic brain injury should be used in preference to shaken baby syndrome, which implies a specific mechanism of injury.

After the history, examination, and investigations have been considered the following conclusions about the cause of brain injury can be reached: It is characteristic of, consistent with, possibly due to, or not the result of, non-accidental trauma.