It is an important clinical diagnosis, because it is a potentially reversible cause of dementia. NPH differs from other causes of adult hydrocephalus. An increased subarachnoid space volume does not accompany increased ventricular volume. Clinical symptoms result from distortion of the central portion of the corona radiata by the distended ventricles. This includes the sacral motor fibers that innervate the legs and the bladder, thus explaining the abnormal gait and incontinence.
Dementia results from distortion of the periventricular limbic system.
Hakim first described the mechanism by which a normal or high-normal CSF pressure exerts its effects. Pressure X Area, increased CSF pressure over an enlarged ependymal surface applies considerably more force against the brain than the same pressure in normal-sized ventricles. Normal pressure hydrocephalus may begin with a transient high-pressure hydrocephalus with subsequent ventricular enlargement. Intermittent intracranial hypertension has been noted in some patients. Some authors prefer the term extraventricular obstructive hydrocephalus.