What are the different types of hydrocephalus?
Communicating hydrocephalus occurs when the flow of CSF is blocked after it exits the ventricles. The word “communicating” refers to the fact that CSF can still flow between the ventricles, which remain open. Non-communicating hydrocephalus - also called obstructive hydrocephalus - occurs when the flow of CSF is blocked along one or more of the narrow passages connecting the ventricles. One of the most common causes is aqueductal stenosis, a narrowing of the aqueduct of Sylvius, a small passage between the third and fourth ventricles in the middle of the brain. Normal pressure hydrocephalus (NPH) is a form of communicating hydrocephalus that can strike people at any age, but it is most common among the elderly. It may result from a subarachnoid hemorrhage, head trauma, infection, tumor or complications of surgery. However, many people develop normal pressure hydrocephalus even when none of these factors are present for reasons that are unknown. In that case it is called idiopathic normal pressure hydrocephalus. Hydrocephalus may be also be classified as congenital or acquired. Congenital hydrocephalus is present at birth and may be caused by either events or influences that occur during fetal development, or genetic abnormalities. In rare cases, congenital hydrocephalus may not cause symptoms in childhood but only manifest in adulthood and may be associated with aqueductal stenosis. Acquired hydrocephalus develops at the time of birth or at some point afterward. This type of hydrocephalus can affect individuals of all ages and may be caused by injury or disease. Hydrocephalus ex-vacuo is another form of hydrocephalus that does not fit exactly into the categories mentioned above and primarily affects adults. Hydrocephalus ex-vacuo occurs when stroke, degenerative diseases like Alzheimer's disease or other dementias or traumatic injury cause damage to the brain. In these cases, brain tissue may actually shrink.