The Swedish shaken baby syndrome report and review: what does the latest knowledge tell us?

It is almost fifty years since Norman Guthkelch first introduced the hypothesis that the whiplash injury produced through shaking a baby causes subdural haematoma (SDH), retinal haemorrhages (RH) and encephalopathy, referred to as ‘the triad’ (1). The topic has never ceased generating heated controversy and acrimonious debates. At the core of the dispute is not whether shaking can cause devastating lethal injury, as it can certainly do (2,3). The main controversy resides in the value of the ‘triad’ as categoric evidence of abusive head trauma (AHT) by shaking when no other credible explanations are found. The mechanism of SBS/AHT as initially proposed involves rotational and acceleration/deceleration movement of the brain within the cranium, producing shearing of the nerve fibres of the brain and tearing of the cortical bridging veins into the potential subdural ‘space’ (1). Geddes et al. (4) showed that the brain pathology in infants thought to have been shaken was due to hypoxia and ischaemia rather than traumatic tearing of axons and that damage to the craniocervical junction could account for apnoea, leading to hypoxia and brain swelling. The debate further increased when Geddes et al. (5) suggested that the cause of the subdural bleeding in some cases of infant head injury is not the traumatic rupture of bridging veins, but a phenomenon of immaturity involving intradural bleeding. What became known as the ‘Geddes hypothesis’ is that thin film SDH and RH could be caused by severe hypoxia in association with brain swelling and raised central venous pressure. Significantly, in cases with no evidence of trauma, the possibility of a natural disease process precipitating the same sequence of events was implied. The Geddes ‘hypothesis’ (5) was heavily criticised by traditionalists who argued that traumatic disruption of bridging cerebral veins and vitreoretinal shearing injury explain RH and SDH. To add to the debate, in 2005, the Court of Appeal found the Geddes Hypothesis ‘not credible’, which greatly influenced the medicolegal community, even though the Courts do not have medical expertise and the courtroom is not a suitable forum in which to debate contentious medical hypotheses. Interestingly, recent studies have shown that (i) there is a rich intradural vascular plexus, (ii) SDH may result from tears in the thin-walled segments of the large bridging veins as they pass through the dural border layer as well as from rupture of the narrow vessels of the dural venous plexuses, leading to thin film bleeding in the subdural ‘compartment’ and that (iii) thin film SDH can also be seen in young infants with hypoxic–ischaemic encephalopathy not related to trauma (6). Therefore, the thin film of SDH in the triad appears to be unreliable as evidence of AHT/SBS. It is fascinating that despite a shift in the paradigm, the debate concerning the power of the ‘triad’ as evidence of AHT remains unchanged. The Swedish Agency for Health Technology Assessment and Assessment of Social Services (SBU) conducted a systematic literature review aiming to determine the diagnostic accuracy of the triad in detecting whether an infant had been shaken (7). Lynøe et al. (7) identified 3773 abstracts, 1064 were considered relevant and read as full texts, and 30 studies were ultimately included. Of these, 28 were assessed as having a high risk of bias related to methodological shortcomings and circular reasoning when classifying shaken baby cases and controls. Only two studies had a moderate risk of bias; both used confessions and convictions when classifying shaken baby cases, but their different designs made a meta-analysis impossible. None of the studies had a low risk of bias, and circular reasoning was a common feature. The conclusions of the review study (7) were that there was insufficient scientific evidence to diagnose isolated shaking using the triad as the diagnostic criterion. In a more recent publication, Lynøe et al. (8) reiterated that the two main conclusions of their previous study (7) were as follows: (i) the insufficient scientific evidence on which to assess the diagnostic accuracy of the triad in identifying traumatic shaking and (ii) the limited scientific evidence that the triad and can be associated with traumatic shaking. Lynøe’s et al. (7) results fuelled the discussion and widened the differences, involving influential medical societies and leading to the publication of numerous responses both in support and in disagreement (9,10). Notably, one of the studies that followed (10) reported a low incidence of AHT in Sweden. In a national study covering a 20-year period, the authors were unable to identify any infant with SDH without perinatal risk factors, significant disease or findings consistent with nonimpact head trauma. Moreover, the authors of this study (10) raised the question that