Normal pressure hydrocephalus is seen in aging adults and has frequently been associated with Alzheimers’s disease, but is currently considered to be a separate and distinct condition of the brain. Interestingly, it has also been associated with Parkinson’s disease (PD) but not as frequently. The difference probably has to do with the way we diagnose PD, which I will explain later.
The term hydrocephalus comes from two greek words: cephalus meaning head and hydros meaning water. Medically speaking hydrocephalus is an abnormal expansion of the ventricles (ventriculomegaly) within the brain that is caused by the accumulation and increase in pressure of cerebrospinal fluid (CSF). Normal pressure hydrocephalus is a specific kind of hydrocephalus in which the ventricles enlarge at the expense of brain tissue while CSF pressure remains within normal ranges. Some researchers now support the idea of referring to NPH as anything that blocks CSF movement and/or causes CSF to accumulate or back up with or without ventriculomegaly.
In addition to Alzheimer’s and Parkinson’s disease, normal pressure hydrocephalus has been associated with many diverse and interesting conditions such as rheumatoid arthritis, lupus erythematosis, schizophrenia and manic depression. These associations beg further investigation. What could possibly be the common denominator in these conditions? I believe it has to do with venous drainage problems in the brain.
To better understand the affect of NPH on the adult brain, it is easier to start by looking at hydrocephalus in infants and children. The reason for this is because the affects of hydrocephalus in children are so easy to see, understand and appreciate as far as what it does to the delicate tissues of the brain. See skull deformation and correction for further information.
In a child, hydrocephalus can cause mental retardation. In an adult, normal pressure hydrocephalus causes dementia the same as in Alzheimer’s disease. Among other things, it can also cause pressure on the belly side of the brainstem and compress structures, such as the substantia nigra which can cause tremors such those seen in Parkinson’s disease.
Hydrocephalus in Children
Hydrocephalus occurs in children for several reasons but is most frequently due to cerebrospinal fluid (CSF) flow becoming blocked.(See arachnoid granulations page.) Other causes are overproduction, which is rare or venous drainage insuffienciency which happens occasionally. Consequently, it causes the volume of CSF in the ventricles of the brain and head to increase in size. It also causes an increase in the size of all the spaces of the brain, such as the fissures and sulci located between the lobes and gyruses that form the folds in the brain’s surface.
Unlike adults, the head can enlarge in children because the special joints of the skull, called sutures, are still open. As the volume of CSF increases the size of the ventricles, the membranous bones that form the cap of the skull expand increasing the size of the head. The ventricles are the dark areas in the pictures below.
The enlargement of the ventricles stretches the inner and outer surfaces of the brain. At the same time the increase in volume and pressure of CSF in the ventricles, fissures and sulci spaces compress the brain. The outcome of hydrocephalus in children is mental retardation and life expectancy is short even though it is much longer now with today’s modern shunts.
Normal Pressure Hydrocepalus or NPH
NPH occurs in aging adults and likewise causes the ventricles, fissures and sulci spaces of the brain to increase in size. As was mentioned, in contrast to children, the special joints of the skull called sutures are closed so the head cannot enlarge and remains normal in size.
NPH also similarly stretches the inner and outer surfaces of the brain as the ventricles enlarge as depicted in the picture below. At the same time the increase in CSF volume compresses the brain, and the outer surface gets further crushed against the inside surface of the cranial vault of the skull.
Rather than the mental retardation seen in children, in adults, NPH causes dementia.
The substantia nigra page may also be of interest to those interested in NPH.