The brain has two circulations.
- Blood which carries oxygen, glucose, nutrients and proteins which brain cells need to survive comes to the brain through arteries from the heart and returns waste to the heart through veins.
- A second circulation consists of cerebrospinal fluid (CSF) that collects in a series of larger cavities called ventricles which are connected by much narrower pathways. Fluid first collects in the the two lateral ventricles deep in the top portion of the brain called the cerebral hemispheres, then progresses to the third and then fourth ventricle in the midportion of the brain. After this point the CSF exits from the center of the brain to pass external to the brain surface and moves up along the brain to be reabsorbed into the blood stream over the top of the brain through a filtering system called the arachnoid villi. Every 24 hours about 500cc of CSF is produced and reabsorbed. Unlike blood which has a lot proteins and complex chemicals, the CSF is normally clear without much protein.
Functions of CSF
- The CSF not only plays a role helping to deliver nutrients and take away waste from brain cells but also some other more unique functions critical to the brain's well being.
- As the brain is contained in a closed container of fixed size, the skull, it is very suspectible to changes in pressure. Pressure in the brain space is critical, allowing proper blood flow to the brain. If the pressure goes higher than the blood pressure then blood cannot enter the brain and brain cells will die within a few minutes. Some CSF in the space helps provide a medium to support brain cells floating in liquid to maintain their function.
- lt also acts as a sort of shock absorber.
However if CSF collects in excess and is not reabsorbed, then pressure inside the skull can increase to damage brain cells or even kill them by depriving them of oxygen and glucose.
Causes of Hydrocephalus
- An excess of CSF collecting in the ventricles causes hydrocephalus which comes from the Greek words for water, “hydro”, and head, “cephalus”.
- Until the age of 2 years, the skull is not yet a solid container but instead consists of bone plates with seams for expansion.
- Thus hydrocephalus in infants and young children often presents with an abnormally large head which continues to grow to abnormal sizes.
Two Main Forms of Hydrocephalus
- An abnormal collection of CSF in the brain basically occurs in two main forms.
- If there is an obstruction of the flow of the fluid anywhere from the lateral ventricles to the fourth ventricle, then it is called obstructive hydrocephalus. This may be caused by birth defects occuring during development before birth, tumours, injury, hemorrhage, or infection.
- Alternatively, there may be no obstruction but instead the arachnoid villi may be dysfunctional and not allowing reabsorption which is called communicating hydrocephalus. Communicating hydrocephalus may have no discernible cause or may happen following hemorrhages, infections, or trauma to the brain.
After the age of 2 years, the skull bone plates join together so that the head can no longer enlarge in response to CSF accumulation. Subsequently, the pressure inside the skull, called intracranial pressure (ICP), increases and thus reduces the blood flow to the brain as well as causing physical changes to the brain. Deformity of the nerves from increased pressure causes loss of vision, difficulty in thinking, difficulty with coordination and loss of memory. If unchecked it can lead to shifts of brain structures, called herniations, which can result in permanent coma or death.
If the pressure remains above that which allows blood flow into the brain for even a few minutes, then a condition where the brain essentially dies, called brain death, will occur.
Treatment for Hydrocephalus
- For the past several decades the mainstay of treatment for hydrocephalus has been surgery, to divert the abnormal collection of CSF from the brain to another cavity in the body where the fluid could be absorbed.
- In the past this diversion was usually to the heart or cavity holding the lungs.
- But now, most commonly what is done is to place tubing with a pressure or flow control device from the brain to the abdomen.
- The fluid goes into the space, the peritoneal cavity, between the abdominal organs where it is usually absorbed without any problem.
- This diversion may sometimes only need to be temporary if the main cause such as tumour, bleeding, or infection can be successfully treated.
- If the main cause cannot be treated directly or has been severe, then often the diversion will need to be permanent.
- Recently surgery has been developed which involves opening a channel to treat obstructions between the ventricles by using scope systems in narrow instrument tubes (Ventricular endoscopic fenestration).
- For some patients this procedure can avoid the need for placement of a permanent ventricular peritoneal shunt device.
- Early treatment of hydrocephalus can often avoid death or severe neurologic dysfunction in many patients, while some patients will have a burden of diminished capacity.
There are thousands of people around the world living independent and useful lives following successful surgery for hydrocephalus.
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