Every day, the body makes roughly 600–700 ml of CSF, and about the same amount is reabsorbed into the bloodstream. Hydrocephalus is due to an imbalance between the amount of fluid produced and its absorption rate. Enlarged ventricles put increased<unk>  on the adjacent cortical tissue and cause myriad effects in the patient, including distortion of the fibers in the corona radiata. This leads to an increase in intracranial<unk>  (ICP). The ICP gradually falls, but still remains slightly elevated, and the CSF<unk>  reaches a high<unk>  level of 150 to 200 mm H2O. Measurements of ICP, therefore, are not usually elevated. Because of this, patients do not exhibit the classic signs that accompany increased intracranial<unk>  such as headache, nausea, vomiting, or altered consciousness, although some studies have shown<unk>  elevations to occur intermittently. The exact pathogenesis is unknown, but consensus on some mechanisms include: * An imbalance exists between production and resorption of CSF. * The resistance to CSF outflow is often elevated. * The disease is not caused by overproduction of CSF or obstruction of CSF flow at the ventricles. The syndrome is often divided into two groups, primary (also called idiopathic) and secondary, based on cause. The underlying etiology of primary<unk>  has not yet been identified. Primary<unk>  affects adults age 40 years or older, most commonly affecting the elderly. Secondary<unk>  can affect persons of any age and occurs due to conditions such as subarachnoid hemorrhage, meningitis, brain surgery, brain radiation, or traumatic brain injury.
Normal pressure hydrocephalus
Low pressure hydrocephalus
Lewy body dementias
Early-onset Alzheimer's disease
Multiple system atrophy
Frontotemporal dementia
Vascular dementia
Dementia with Lewy bodies