Changes in the subarachnoid space precede ventriculomegaly in idiopathic normal pressure hydrocephalus (iNPH).

We report on an 80-year-old woman who had shunt-responsive idiopathic normal pressure hydrocephalus (iNPH). Her brain MRI showed an initial change in the subarachnoid space (a disproportional narrowing of the subarachnoid space at the cerebral high convexities) at the age of 70 years, followed by enlargement of the ventricles (Evans index: 0.31) at the age of 78. The observation suggests that changes in the subarachnoid space may precede ventricular enlargement in iNPH.