A mild head injury is defined by a hospital emergency department, as a head injury not severe enough to need admission for observation. 78 children were compared with 86 controls that had a minor injury in other areas. Children with mild head injury, at six months and one year were found to have scored less on a visual puzzle test and were more likely to have another mild head injury. At 6.5 years, they still scored less than controls.
Wrightson P. McGinnV, Gronwall D. J Neurol Neurosurg Psychiatry. 1995 (Oct);59 (4): 375-380