With hydrocephalus, including congenital hydrocephalus, there is an imbalance in how much cerebrospinal fluid (CSF) is made and absorbed, or in how it flows. One way to classify this condition is by how the imbalance occurs. There are two main ways:

• Nonobstructive, or communicating, hydrocephalus occurs when the CSF flows out of the brain ventricles and into the spinal canal, but it is not reabsorbed normally by the tissue surrounding the brain and spinal cord. Sometimes this type of hydrocephalus corrects itself.
• Obstructive, or noncommunicating, hydrocephalus occurs when the CSF does not flow properly between or out of the brain ventricles because of an obstruction, such as from a malformation or narrowing.

Sometimes a child with congenital hydrocephalus has problems from both the nonobstructive and obstructive forms.

In very rare cases, the brain tissue makes too much CSF and the body can't properly absorb or distribute the high amount of fluid. This is called overproduction hydrocephalus.