In the early sixties, a young neurosurgeon by the name of Hakim observed that certain patients who were suffering from incontinence, problems walking and mild dementia had something in common. They appeared to have excess amounts of fluid (hydro-) in the brain (-cephalus).The amount of fluid in the brain can rise in several diseases including stroke and brain injury. However in these conditions, because the brain sits inside the skull (a closed, solid, structure), the pressure in the head usually rises. The condition observed by Hakim is special in that the measured pressure in the head is nearly normal. These features led to the name "Normal Pressure Hydrocephalus"

In this article, the authors described the success of surgical intervention in relieving the symptoms of their patients. Simply put they placed a "shunt", or tube into the excess fluid, which allows it to drain away elsewhere in the body. They found that their patients showed a dramatic improvement in both walking, continence and thought processes.

Since these early descriptions, approximately 800 scientific articles have been written about the condition. However, the exact cause of the problem has evaded researchers. The most likely theory to be put forward is one concerning a deficient absorption of the fluid which normally bathes the brain, the "cerebrospinal fluid" or CSF.

CSF is a salt solution produced by the coverings of the brain to help protect it. Without CSF the brain would be constantly hitting the inside of the skull - the fluid acts as a shock-absorber. There is a constant turnover of this fluid, i.e. CSF is constantly being made, and constantly being reabsorbed. If anything were to block the reabsorption of the fluid, and yet production continues at the same rate, then clearly the amount of CSF would increase. This is a possible cause of NPH. Sometimes NPH follows a known problem where these processes are clearly disturbed - including subarachnoid hemorrhage, infection, trauma and brain tumors. However a large number of patients have no identifiable cause, and these cases are called "Idiopathic NPH".

One of the big questions is why, if the amount of CSF is increasing, does the pressure in the head not rise? Again, the answer to this is not known. However, it might be because the process is happening gradually, and therefore increasing amounts of fluid begin to wear away at the brain tissue, slowly replacing it. It is this loss of brain tissue which is believed to cause the symptoms associated with NPH.

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Maintained by: Andrew Beaumont MD

Department of Neurosurgery
Updated August 2003, Rev 3.0