Shaken baby syndrome: the quest for evidence.

Shaken baby syndrome (SBS), characterized by the triad of subdural haemorrhage, retinal haemorrhage, and encephalopathy, was initially based on the hypothesis that shaking causes tearing of bridging veins and bilateral subdural bleeding. It remains controversial. New evidence since SBS was first defined three decades ago needs to be reviewed. Neuropathology shows that most cases do not have traumatic axonal injury, but hypoxic-ischaemic injury and brain swelling. This may allow a lucid interval, which traumatic axonal injury will not. Further, the thin subdural haemorrhages in SBS are unlike the thick unilateral space-occupying clots of trauma. They may not originate from traumatic rupture of bridging veins but from vessels injured by hypoxia and haemodynamic disturbances, as originally proposed by Cushing in 1905. Biomechanical studies have repeatedly failed to show that shaking alone can generate the triad in the absence of significant neck injury. Impact is needed and, indeed, seems to be the cause of the majority of cases of so-called SBS. Birth-related subdural bleeds are much more frequent than previously thought and their potential to cause chronic subdural collections and mimic SBS remains to be established.