What is the medical definition of hydrocephalus?The brain and spinal cord are surrounded by a clear fluid called cerebrospinal fluid (CSF). This fluid is produced and stored in cavities in the brain called ventricles. It circulates around the brain, moving from ventricle to ventricle. The purposes of the fluid are to cushion and protect the brain and spinal cord, to supply them with nutrients, and to remove some of their waste products. Any excess fluid drains away from the brain and is absorbed by other tissues.Hydrocephalus is a condition in which there is too much CSF in the ventricles. This occurs when the natural system for draining and absorbing extra CSF does not work right. The ventricles enlarge to accommodate the extra fluid and then press on different parts of the brain, causing a number of different symptoms. Hydrocephalus has many different 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 occurs in adults, usually older adults. The average age of people with NPH is older than 60 years. NPH is different than other types of hydrocephalus in that it develops slowly over time. The drainage of CSF is blocked gradually, and the excess fluid builds up slowly. The slow enlargement of the ventricles means that 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 term "normal pressure" is somewhat misleading.)Is fluid on the brain serious?The parts of the brain most often affected in NPH are those that affect 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. Other symptoms include abnormal gait (difficulty walking), inability to hold urine (urinary incontinence), and, occasionally, inability to control the bowels.What are the long term effects of hydrocephalus?The dementia symptoms of NPH can be similar to those of Alzheimer disease. The walking problems are similar to those of Parkinson disease. Experts believe that many cases of NPH are misdiagnosed as one of these diseases. The good news is that, unlike Alzheimer disease and Parkinson disease, NPH can be reversed in many people with appropriate treatment. But first, it must be correctly diagnosed. What does normal pressure hydrocephalus look like? T2-weighted MRI showing dilatation of ventricles out of proportion to sulcal atrophy in a patient with normal pressure hydrocephalus. The arrow points to transependymal flow. CT head scan of a patient with normal pressure hydrocephalus showing dilated ventricles. The arrow points to a rounded frontal horn.