Although other conditions can cause hydrocephalus, it many times begins with IVH. Then there is a disturbance in CSF dynamics, which leads to progressive dilation (swelling) of the brain ventricles, which then results in hydrocephalus.
The progression of hydrocephalus is as follows:
- IVH (or other brain insult)
- Disturbance in CSF dynamics
- Swelling of the ventricles
IVH AND OTHER BRAIN INSULTS
Hydrocephalus often begins with an injury to the brain that causes IVH. Premature babies are more susceptible to IVH because blood vessels and other parts of their brains are fragile. Conditions that can cause IVH in a term or preterm baby include the following:
- Hypoxic ischemic encephalopathy (lack of oxygen or blood flow to the brain)
- Abnormal changes in blood pressure
- Trauma from prolonged labor
- Trauma from a difficult birth, which can occur when a baby is large for its gestational age (macrosomic), the mother has a small pelvis or the baby’s head or body cannot easily fit through the birth canal (CPD), or forceps or vacuum extractors are used to facilitate delivery
- Oxygen deprivation or head trauma from use of Pitocin or Cytotec
- Abnormal presentation that causes head trauma, such as a breech or face presentation
*The most common cause of acquired (after birth) hydrocephalus in a baby is a germinal matrix hemorrhage (GMH), also known as a periventricular-intraventricular hemorrhage. GMH occurs primarily in premature infants. This is because activity in the germinal matrix peaks at 8 – 23 weeks of gestation. The germinal matrix helps create the fully-formed brain; cells develop and migrate out of this structure during brain development. Damage to the germinal matrix at weeks 8-23 can cause severe brain damage and death. A GMH occurs when there is bleeding into the part of the germinal matrix that is connected to the lateral ventricles. When this occurs, there may be subsequent rupture into the lateral ventricles. A GMH causes the ventricles to be filled with blood and degradation products, and this, among other things, causes dilation of the ventricles. GMH leads to a lot of stress on the areas around it, as well as congestion of the blood vessels. All of these factors can lead to white matter injury and permanent brain damage.
Other conditions that can lead to hydrocephalus include the following:
- Intrauterine infections, such as syphilis, cytomegalovirus (CMV), rubella and toxoplasmosis
- Brain infections, such as meningitis or viral infections.
- Hemorrhage (severe and sudden bleeding) into the subarachnoid space, which is the space in between the layers that cover the brain.
- Hemorrhage into the ventricles of the brain, which can be caused by ruptured vessels and trauma.
DISTURBANCE IN CSF DYNAMICS, SWELLING OF THE VENTRICLES AND BRAIN DAMAGE
CSF is a liquid that completely surrounds the brain and spinal cord tissue. The liquid circulates throughout the brain before being reabsorbed into the blood through the brain ventricles. In normal conditions, the absorption of CSF generally matches the volume of CSF being formed each day. CSF protects the brain and spinal cord against any jarring forces, acting as a shock absorber. CSF is comprised of a mixture of proteins that supports brain cell development.
Hydrocephalus results from an imbalance between the intracranial CSF inflow and outflow, and is most often caused by inadequate absorption of CSF or obstruction of CSF circulation. When there is severe insult to the brain due to conditions such as oxygen deprivation (hypoxia), trauma or infection, the brain swells. Although the initial swelling may subside, the injury may result in damage to one or more ventricles, causing a blockage or damage to tissue responsible for absorption of CSF. Since the body is constantly making CSF, any delayed absorption or obstruction results in buildup of the fluid, causing the ventricles to swell. This, in turn, leads to pressure on surrounding brain matter, pushing aside the soft tissue of the brain and leading to further brain damage.
More specifically, hydrocephalus and brain damage can occur due to the following events:
- Dilation of the ventricles usually is uneven. The front and back horns of the ventricles typically enlarge first, and to the greatest extent. This enlargement disrupts the lining of the ventricles, which allows CSF to move directly into the brain tissue. This reduces a lot of CSF pressure, but also leads to fluid going into the spaces within the membranes that cover the brain, with progressive involvement and damage of white matter.
- As the hydrocephalus progresses, fluid build up and ischemia (restricted blood flow) develop in the white matter that surrounds the ventricles (the periventricular brain tissue). This leads to destruction of the white matter.
- With further progression of this process, the membrane that covers the brain can become obliterated over the brain hemispheres. (The gray brain matter at the cortex may be reduced, but gray matter is better preserved than white matter.) This eventually leads to the vascular system becoming compressed, and pressure in the veins increasing in certain areas.
- The vessels in the brain become weak, and there is a loss of vessels in the white matter, which leads to white matter destruction. Damage to the white matter also is caused by changes in cells that are part of the central nervous system.