Hydrocephalus is a condition in which there is an excess volume of cerebrospinal fluid in or around the brain.
Cerebrospinal Fluid Circulation
The fluid is cerebrospinal fluid (CSF) which is produced inside the brain. The fluid is produced inside ventricles of the brain by a structure called the choroid plexus. There are four ventricles. There is a larger lateral ventricle on each side which connect to the smaller third and then fourth ventricle. The ventricles connect through narrow passages. The cerebral aqueduct is particularly narrow and connects the third and fourth ventricles.
CSF circulates through the ventricles of the brain, and out through the bottom of the brain where it enters the subarachnoid space. This space around the brain also extends through the spinal canal and surrounds the spinal cord. The fluid is absorbed back into the blood stream through structures called arachnoid villi.
CSF is produced constantly by the choroid plexus. In adults the rate of CSF production is about 22 mls per hour. Therefore, about 500mls per day is produced and absorbed. The balance between production and absorption is important.
What are the types of hydrocephalus?
Hydrocephalus may be congenital or acquired:
Hydrocephalus may also be communicating or non-communicating:
There are also other ways to classify hydrocephalus based on the type of presentation. For instance, Normal pressure hydrocephalus can happen to people at any age, but it is most common among the elderly. It may result from a subarachnoid haemorrhage, head trauma, infection, tumour, or complications of surgery. NPH is a communicating hydrocephalus and despite the volume of CSF being increased, the pressure of the fluid is not elevated.
What are the symptoms of hydrocephalus?
The symptoms will depend on the age of the patient and cause of the hydrocephalus. In babies, hydrocephalus may cause enlargement of the head or macrocephaly. This occurs because in babies, the bones of the skull are soft and not yet fused together. The head can therefore expand. After about one year of age the bones of the skull fuse and this is then much less likely.
The most common symptoms in patients with hydrocephalus are those of raised intracranial pressure which are headache, nausea and vomiting. In some cases, this can lead to drowsiness, coma or even death if not treated. It may also cause loss of vision.
In normal pressure hydrocephalus the symptoms are not headaches but rather a gait disorder with a short, shuffling gait and imbalance, cognitive decline and urinary incontinence.
How is hydrocephalus diagnosed?
Hydrocephalus is diagnosed on the basis of a scan. In babies an ultrasound may demonstrate hydrocephalus. A CT scan will also show enlargement of the ventricles. However, an MRI scan is the most useful test for determining not only the severity of the hydrocephalus but also the cause.
How is hydrocephalus treated?
The treatment of hydrocephalus will ultimately depend on the cause. A tumour causing obstructive hydrocephalus for instance will require a procedure to remove the tumour and this may well treat the hydrocephalus as well.
Otherwise, hydrocephalus is most commonly treated using a CSF shunt. This allows the CSF to be drained from the ventricles to another part of the body for absorption. The most common shunt is a ventriculoperitoneal shunt.
In some cases, an endoscopic third ventriculostomy may be used to treat hydrocephalus. This is most useful in obstructive hydrocephalus, particularly that of aqueduct stenosis.
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