In Hydrocephalus ex vacuo, the compensatory enlargement of ventricles and an increase in CSF volume due to brain atrophy is seen in-

Hydrocephalus ex vacuo Insignificant cortical atrophy, there is compensatory ventricular enlargement secondary to loss of parenchyma → Hydrocephalus ex vacuo. This can be seen in Alzheimer disease and Pick disease. - Anderson 10th/ep. 2740.