Dr. Greene’s Answer:
Hydrocephalus is a condition where spinal fluid (CSF), doesn’t circulate normally.
Typically, the brain and spinal cord are cushioned in a bath of CSF. In a baby there is usually about 10 tsp of this fluid (in an adult about 5 oz). It is formed within the brain in the spaces called ventricles. It circulates through the ventricles, exiting from the 4th ventricle and then flowing over the surface of the brain. In the end, it is absorbed and disappears.
In obstructive (noncommunicating or internal) hydrocephalus, there is a blockage in the ventricle system. Fluid builds up in the ventricles and puts pressure on the brain from within. A shunt is often needed to correct the problem.
In communicating hydrocephalus (nonobstructive or external), the CSF flows fine, but it is not absorbed at the end. Fluid builds up outside the brain, and in a baby the pressure makes the skull grow larger.
Communicating hydrocephalus is most common in premature babies who have had a bleed in the tissue that normally absorbs the CSF (a subarachnoid bleed).
Treatment can vary quite a bit (medicines to reduce the amount of CSF formed, surgery to shunt the fluid elsewhere, or wait and see if the situation improves).
As long as the hydrocephalus is present, it will affect the shape of the growing forehead and skull, but this can improve once the hydrocephalus is gone.