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What are arachnoid cysts?

Arachnoid cysts are sacs filled with spinal fluid that can grow in between the brain or spinal cord and the arachnoid membrane that covers them. Most of these cysts are found on the brain; spinal cord cysts are much more rare.

There are two types of arachnoid cysts:

  • Primary arachnoid cysts are cysts that a child is born with. They are the most common type.
  • Secondary arachnoid cysts can develop after a head injury or brain surgery. They are less common.

Symptoms & Causes

What causes arachnoid cysts?

Doctors aren’t sure exactly what causes arachnoid cysts, but they think the cysts may form if there is a tear in the arachnoid membrane that surrounds the brain and spinal cord. Boys are four times more likely to have arachnoid cysts than girls.

What are the symptoms of an arachnoid cyst?

Some children with arachnoid cysts will never have symptoms. Most people who will have symptoms usually have them before age 20, though symptoms often start before age 1.

Arachnoid cysts can cause a large range of symptoms, depending on where the cysts are located and their size. Some common symptoms include:

  • Headaches
  • Nausea and vomiting
  • Seizures
  • Hearing and vision problems
  • Dizziness
  • Trouble with balance and walking
  • Leg or back pain
  • Numbness or tingling in the arms or legs

Diagnosis & Treatments

How are arachnoid cysts diagnosed?

Arachnoid cysts are usually diagnosed with a complete exam and imaging tests to see the cysts. These tests may include:

How are arachnoid cysts treated?

Many children with arachnoid cysts don't need any treatment. In most cases, treatment is only recommend if the cysts are causing symptoms. If your child needs treatment there are a few options:

  • Surgery to remove the cyst or to open the cyst so it can be reabsorbed into the spinal fluid.
  • Placing a shunt (a thin tube shaped like a straw) into the cyst to drain the fluid into another part of the body, such as the stomach.

How we care for arachnoid cysts

Most arachnoid cysts cause no problems or symptoms and don’t need any treatment. If the cysts do cause symptoms, they may need surgery.

Our specialists at Boston Children's Hospital Department of Neurosurgery can assess whether or not your child's arachnoid cysts need treatment. If your child does need surgery, our surgeons use minimally invasive techniques whenever possible, for a faster recovery and minimal scarring.