Because of this, patients do not exhibit the classic signs that accompany increased intracranial pressure such as headache, nausea, vomiting, or altered consciousness, although some studies have shown pressure 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 NPH has not yet been identified. Primary NPH affects adults age 40 years or older, most commonly affecting the elderly. Secondary NPH can affect persons of any age and occurs due to conditions such as subarachnoid hemorrhage, meningitis, brain surgery, brain radiation, or traumatic brain injury. Diagnosis
Patients with suspected NPH should have typical symptoms in addition to ventricular enlargement on neuroimaging. The international evidenced-based diagnostic criteria for primary NPH are:
Gradual onset after age 40 years, symptoms duration of ≥ 3–6 months, clinical evidence of gait or balance impairment, and impairment of cognition or urinary incontinence
Imaging from magnetic resonance imaging (MRI) or computed tomography (CT) is needed to demonstrate enlarged ventricles and no macroscopic obstruction to cerebrospinal fluid flow.
Among individuals with dementia, the incidence of NPH is thought to be between 2 and 6%. See also
Low pressure hydrocephalus

References
External links
The Normal Pressure Hydrocephalus Center at Johns Hopkins Bayview Medical Center
Normal Pressure Hydrocephalus at Cleveland Clinic
normal_pressure_hydrocephalus at NINDS
When it really is NPH at Likvor
Hydrocephalus in Adults at Spina Bifida Resource Center