Arachnoid Cysts

There are three membranes that cover the brain and spinal cord, one of them is the arachnoid membrane. Sometimes little fluid filled sacs form between the brain or spinal cord and the arachnoid membrane, these are called arachnoid cysts. Typically, the fluid in the sacs is cerebrospinal fluid, which is the fluid that surrounds the spinal cord and brain to protect and nourish them.

Most arachnoid cysts form in the head between the brain and the skull. They can also develop in the brain, usually in the spaces called ventricles, areas that circulate cerebrospinal fluid through the brain. Though rare, cysts can also form on or around the spinal cord.

There are two types of arachnoid cysts, primary and secondary. Primary arachnoid cysts develop in the early weeks of pregnancy so they are present when the baby is born; this is what we call a congenital condition. They are also the most common form of arachnoid cysts. Secondary arachnoid cysts occur after a child is born and are often the result of a head injury, meningitis, tumors or a complication of certain types of brain surgery.

Males are four times more likely to be born with an arachnoid cyst than females. The most common type of arachnoid cyst is congenital, meaning the child develops the cyst before birth. There doesn't seem to be a socio-economic or geographic link.

Many people with arachnoid cysts never develop symptoms. For those who do, the symptoms will depend on whether the cyst is around the brain or around the spinal cord.

The most common symptoms for arachnoid symptoms around the brain are caused if a cyst grows larger or if bleeding into the cyst occurs, and might include:

Headache
Nausea and vomiting
Seizures
Hearing disorders
Visual problems
Vertigo (excessive dizziness)
Walking and balance disorders (excessive clumsiness)

Because they may compress the spinal cord or nerve roots, common symptoms of arachnoid cysts around the spinal cord may involve:

Increasing back and/or leg pain
Tingling and/or numbness in the arms and/or legs
Weakness in the arms and/or legs
Problems with bladder or bowel control

In addition to a complete medical exam, including a medical history, if your doctor suspects an arachnoid cyst, your child will probably undergo a brain or spinal cord screen. This usually involves an MRI, which is painless and noninvasive. An MRI can help to create a clearer image so that your doctor can distinguish and arachnoid cyst from other types of cysts.

Treatment of an arachnoid cyst depends on location, size of the cyst and your child's symptoms. If there are no symptoms and the cyst is small and not pressing against surrounding tissue, the doctor may choose to simply monitor the cyst. If treatment is required, depending on the location and size of the cyst, the neurosurgeon will perform either a fenestration, which is a minimally invasive microsurgery that will allow the cyst to drain. The fluid will drain into the parts of the brain that contain cerebrospinal fluid and be absorbed into the brain. Your doctor may opt to place a shunt into the cyst to drain the fluid. A shunt drains the fluid by redirecting it to another part of the body, in this case, it usually to our child's abdomen where the fluid is absorbed by the body. Your doctor will talk with you about the best course of treatment for your child.

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Arachnoid Cysts

What are the causes?

Who gets them?

What are the symptoms?

How are they diagnosed?

How are they treated?

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