Hyperostosis cranii ex vacuo in adults: a consequence of brain atrophy from diverse causes.

Hyperostosis cranii ex vacuo is diffuse thickening of the bones of the cranium occurring after successful ventricular shunting in hydrocephalic children, presumably as a compensatory phenomenon. We present three adults with severe brain atrophy and correspondingly severe skull thickening. In each, the cause of cerebral atrophy was well defined, and none had undergone ventricular shunting. In two, brain atrophy resulted from different temporally discrete insults sustained in adult life, ischemic in one and traumatic in the other. In the third case. progressive brain atrophy resulted from a primary neurodegenerative disorder, Hallervordan Spatz disease. Our observations suggest that hyperostosis cranii ex vacuo is a more general phenomenon than has been previously recognized, and point to a relationship between dynamic changes in brain size and skull thickness. We suggest that such relationships should be taken into account in anthropometric evaluation of the skull.