Hyperostosis cranii ex vacuo: a rare complication of shunting for hydrocephalus.

Hyperostosis cranii ex vacuo is a condition that may develop after successful ventricular shunting for hydrocephalus. It is characterized by diffuse thickening of the skull (particularly the inner table) involving the calvarium and the base. It is a diagnosis that distinguishes marked calvarial thickening from thickening of the skull because of other causes. It is an entity that needs to be considered in patients who have diffuse thickening of the skull, have premature closure of sutures, and who have been treated for hydrocephalus in the past.