Although axon damage is known to occur in hydrocephalus, the role that decreased cerebral blood flow (CBF), or cerebral ischemia, plays is still unclear. Reduced CBF has been reported in patients and experimental animals with hydrocephalus, but since the immature brain is less vulnerable to ischemia, these decreases may not be sufficient to produce major damage.

Recently, an interesting phenomenon has been discovered in which brains that have been subjected to mild ischemia develop a resistance to more severe levels of low CBF encountered later. This type of "tolerance" to ischemia seems to be an important form of protection for the brain. Dr. Yuchuan Ding has recently conducted experiments to see if this phenomenon also occurs in hydrocephalus. He compared the amount of axon damage in two groups of animals: one group of normal animals was subjected to 20 minutes of severe cerebral ischemia, and the other had hydrocephalus for 4-8 weeks followed by the same level of severe cerebral ischemia for 20 minutes.

The results showed that there was less axon damage in the group with hydrocephalus, suggesting that tolerance had developed to ischemia during the time the animals were hydrocephalic. Further work in this area is needed, but these preliminary results are encouraging because they suggest that some forms of neural protection may develop naturally in hydrocephalic brains.