Hydrocephalus: An Owner’s Manual Part 3 of 6
Types of Hydrocephalus
The Kinds of Hydrocephalus
In theory, there are two major causes of hydrocephalus: over-production and under-absorption. In reality, over-production is rare, probably less than 1% of cases and generally caused by a tumor of the cells producing CSF.
Under-absorption is the culprit in all common forms of hydrocephalus. In general terms, there are two types:
Obstructive hydrocephalus & non-obstructive hydrocephalus.
Let us look at these two groups separately.
Obstructive hydrocephalus (also known as noncommunicating hydrocephalus) relates to the fact that one of the choke points has been obstructed and therefore CSF is building up behind it. Think of a hose attached to a faucet. Turn the faucet on and crimp the hose with a pair of pliers. The hose is the CSF pathway, the water the CSF itself. The crimp is the choke point being occluded or obstructed. Imagine what would happen if the water continues to flow into the hose and can’t get out the other end: it balloons to the point of bursting. That is obstructive hydrocephalus—continued production of CSF in the face of an obstructed flow pathway. The CSF is being made but can’t get out. In this situation, trouble is bound to develop, usually sooner rather than later. These patients can get very sick, very fast. Within hours.
This situation is commonly caused by an obstruction at the level of the cerebral aquaduct between the IIIrd and IVth ventricle. This is called aquaductal stenosis and is a very common form of hydrocephalus. It is more common in young people and children.
Obstructive hydrocephalus is usually caused by a structural lesion, such as a tumor creating a choke point (which eventually obstructs entirely) or a veil of tissue obstructing the aquaduct. If it is a tumor, surgery to remove the tumor may be possible. However, removal of the tumor does not guarantee resolution of the hydrocephalus.
Nonobstructive hydrocephalus (also known as communicating hydrocephalus) is the second common form of hydrocephalus. Not a structural lesion, there is no issue with the choke points. Consider our hose analogy above. In the normal course of events, water will flow out of the hose, where it is reabsorbed—that is re-circulated—back to the beginning. In nonobstructive hydrocephalus, the problem is that the CSF is not re-circulated, that is, it is not properly reabsorbed into the veins of the head. Think of these veins as filters. In this type of hydrocephalus, the filters are clogged with debris.
Usually this occurs after a bad infection, such as some types of meningitis, or a hemorrhage (bleeding) inside the head. Think of these things as muddying the water, or clogging the CSF.
The result is serious, though often nonobstructive hydrocephalus is better tolerated, perhaps because the obstruction in this case is rarely complete. The patient therefore still has some level of CSF reabsorption.
It may take days, or sometimes weeks to get sick when their shunt fails. Other patients just feel persistently lousy and never get acutely ill. These patients may have low grade headaches and mild cognitive problems (trouble thinking). This is sometimes referred to as subacute hydrocephalus, of which there are other causes as well.
Normal Pressure Hydrocephalus
A third type of hydrocephalus is more mysterious than the others. It is called normal pressure hydrocephalus. In this situation, the pressure is normal but the ventricles are still much enlarged. It is as if the set point for the entire system has been moved, but the brain still suffers.
—Most common in the elderly.
—Sometimes misdiagnosed as alzheimer’s disease or senile dementia.
—Not a lethal condition, even when left untreated or a shunt malfunctions.
—Not an urgent matter and requires a careful evaluation since the risks of shunt placement may be higher in these patients (in fact, in certain situations this risk may outweigh the potential benefit of shunting—such a patient should not be shunted).
—Occasionally a similar condition is seen a month or more following aneurysmal subarachnoid hemorrhage (this is another form of subacute hydrocephalus; patients with such a history will very often benefit from shunt placement).
Disclaimer: The information contained in this blog is simply that, information. I am not doling out specific medical advice. Nothing contained herein is meant to replace a complete evaluation by a qualified member of the medical establishment. This page is nonfiction.