Normal pressure hydrocephalus (NPH) is a condition in which the brain structures called ventricles are abnormally enlarged. Ventricles are filled with fluid known as cerebrospinal fluid (CSF); CSF flows throughout the brain and spinal cord. Symptoms of NPH include impaired cognition, walking abnormalities, and loss of bladder control. The "normal pressure" refers to the measured pressure when a spinal tap is done, and means the measurement is within the normal range. The mechanism causing NPH is frequently impaired CSF absorption, which causes the ventricles to enlarge. Several underlying causes for this condition should be considered in a person with NPH.
Intraventricular and/or Subarachnoid Hemorrhage
An intraventricular hemorrhage is a bleed within the ventricle of the brain. Similarly, a subarachnoid hemorrhage refers to bleeding under the tissue layer of the brain called the arachnoid. According to medical database UpToDate contributor, Dr. Neill R Graff-Radford of the Mayo College of Medicine, these types of bleeds within the brain are the most common causes of NPH. Hemorrhages may occur because of trauma to the brain--for example, from a car accident or severe blow to the head--or because an aneurysm in the brain has begun leaking. An aneurysm is a widening of one of the arteries in the body; a brain aneurysm refers to a widening of one of the arteries in the brain. This abnormal widening occurs because the wall of the artery is weaker than usual; it may either leak blood or burst completely, leading to a major bleed within the head. Both of these potentially life-threatening conditions are associated with the possibility of developing NPH.
Acute or Chronic Meningitis
Meningitis refers to an infection, either bacterial or viral, of the meninges, which are the layers of tissue surrounding the brain. When infection is due to bacteria, the condition is referred to as bacterial meningitis. Common symptoms include a classic triad of fever, neck stiffness, and change in the level of consciousness or mental status. However, once the acute infection has resolved, NPH may occur as a result of this prior infection. Furthermore, other, non-infectious causes of meningitis, such as an inflammatory disease or cancer, may also result in the development of normal pressure hydrocephalus.
Congenital Hydrocephalus
A 1989 study published in the journal "Neurology" reported an interesting finding: NPH was a more common phenomenon among adults with larger-than-normal heads than among adults with normal-sized heads. The authors of the study suggested the possibility that perhaps, larger head sizes are an indication of having been born with hydrocephalus, but not showing symptoms; when the NPH is diagnosed, this may be the congenital hydrocephalus becoming symptomatic for the first time. A later study, published in the journal "Alzheimer's Disease and Associated Disorders" in 2004, found similar results in a study of 30 patients with NPH, and 459 without NPH. These results do seem to suggest that NPH in some adults is a result of congenital hydrocephalus that does not become symptomatic until later in their lives.
Other Causes for NPH
According to Dr. Graff-Radford, if intraventricular and/or subarachnoid bleeds are not the cause for NPH, and meningitis is also not a concern for the patient with NPH, the patient may have viral meningitis that has yet to become symptomatic. In addition, an old head injury that seems to be resolved may also be a less-common cause for NPH. However, it is extremely important to make sure that the more common reasons for development of NPH have been ruled out before considering these less common reasons for normal pressure hydrocephalus.
References
- "Neurology"; Symptomatic congenital hydrocephalus in the elderly simulating normal pressure hydrocephalus; N. R. Graff-Redford and J.C. Godersky; December 1989
- "Alzheimer's Disease and Associated Disorders "; Normal pressure hydrocephalus and large head size; T.A. Krefft et. al.; January-March 2004
- "UpToDate"; Denise S. Basow; 2010
