The tadpole sign, also known as the lollipop sign, refers to a characteristic morphology of post-traumatic bridging vein thrombosis with a rounded "head" and a tapering "tail". The finding demonstrates a high specificity for abusive head trauma, a sub-type of non-accidental injury, and should warrant further investigation into possible non-accidental etiology of injury.
This sign is particularly suggestive of injury secondary to a shaking mechanism (as opposed to axial loading via "slamming"). The characteristic morphology occurs because the combination of the high relative weight of the infant head and weak neck musculature allows for increased torque and thus predisposition to shearing and rupture of small bridging veins in the subdural space and subarachnoid space.
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