[Head injuries in patients with pre-existing skull defects].

The mechanism of impact head injuries has generally been discussed on the basis of the cranium is a rigid box completely filled with incompressible contents. In this paper, two cases of head injuries in patients with severe craniectomized skull defects are reported and their conditions are discussed. The 1st case was a 46 year-old female with a large frontoparietal skull defect following surgery on a brain tumor. While hospitalized, she fell down from her bed (50 cm in height) and suffered strong impact on the craniectomized area. From immediately after the injury, there was flaccid hemiparesis, but CT scans showed no morphological changes. The 2nd case was a 12 year-old female with a major frontal craniectomized skull defect following surgery. She fell down in a corridor at school and suffered an impact injury in the defect area. For several days after the fall, she had a headache and nausea, but there were no other neurological deficits. In CT scans, there were findings of a cortical contusional hemorrhage. Wounds of the skull with a partial defect, i.e. "a semiclosed box" in the narrow sense, cause conditions which are difficult to explain by conventional dynamic traumatology. In this paper, these rare head injuries are discussed on the basis of these two cases experienced by the authors and the literature.