Normal pressure hydrocephalus (NPH) is a condition that affects the brain. It happens when there is too much of a certain kind of fluid in parts of your brain.
Your brain and spinal cord are surrounded by a clear liquid called cerebrospinal fluid (CSF).  This liquid is made and stored in cavities in your brain called ventricles. It circulates around your brain, moving from ventricle to ventricle. The purpose of this liquid is to cushion and protect the brain and spinal cord, supply them with nutrients, and remove some of their waste products. Extra fluid is usually absorbed by veins at the top of the brain.
But when you have hydrocephalus, the natural system for draining and absorbing extra CSF doesn’t work right. The ventricles in an attempt to accommodate the extra fluid, enlarges and begins to press on different parts of the brain, causing a number of different symptoms. Hydrocephalus is traced to several causes, some people are born with the condition, while others develop it during their lives.
Normal pressure hydrocephalus (NPH) is a type of hydrocephalus that is more common amongst older adults. The average age of a person with NPH is 60. What makes NPH different from other types of hydrocephalus is that it develops slowly over time. The drainage of CSF is blocked gradually, and the extra fluid builds up slowly. It causes the ventricles to enlarge slowly and the fluid pressure in the brain may not be as high as in other types of hydrocephalus. However, the enlarged ventricles still press on the brain and can cause symptoms.
The parts of the brain most often affected in NPH are those that control the legs, the bladder, and the “cognitive” mental processes such as memory, reasoning, problem solving, and speaking. This decline in mental processes, if it is severe enough to interfere with everyday activities, is known as dementia. 
The dementia symptoms of NPH can be similar to those of Alzheimer’s disease.  The walking problems are similar to those of Parkinson’s disease.  Experts say that many cases of NPH are misdiagnosed as one of these diseases. Unlike Alzheimer’s and Parkinson’s, NPH can be reversed in many people with appropriate treatment. But first it must be diagnosed correctly, since treatment measures differ.
Causes of Normal Pressure Hydrocephalus
Because NPH develops slowly, it becomes a little more difficult to trace the cause of it. But several things can lead to it, such as:
- A head injury
- Bleeding around the brain (due to a blow to the head)
- A stroke 
- Meningitis 
- Brain tumor 
- Surgery on the brain
Usually any condition that affects the natural system of draining and absorbing CSF can cause NPH.