Arachnoid Cyst

What is an arachnoid cyst? 

Arachnoid cysts are fluid-filled sacs in the arachnoid layer, one of the three membrane layers that protect the brain and spinal cord. They are filled with normal cerebrospinal fluid (CSF) and are not cancerous. Arachnoid cysts are the most common kind of brain cyst. Most arachnoid cysts are found by accident and typically do not cause symptoms or require treatment.

What causes arachnoid cysts? 

• Primary arachnoid cysts are congenital and present at birth. The cause of these cysts is unknown. There may be a genetic component. The most growth occurs during 0-4 years of age. 
• Secondary arachnoid cysts are the result of a small tear in the arachnoid membrane that occurs after a brain injury or trauma.

What are the signs of a symptomatic arachnoid cyst? 

Most arachnoid cysts do not cause symptoms. However, symptoms can appear if the cysts are large enough to cause pressure in the brain or spine. Below are some possible symptoms: 

Arachnoid cysts in the brain may cause: 

• Headaches 
• Dizziness 
• Nausea or vomiting 
• Excessive sleepiness or low energy 
• Seizures 
• Vision problems

Arachnoid cysts in the spine may cause: 

• Back pain 
• Numbness or tingling of the hands or feet 
• Weakness of the arms or legs 
• Gait changes (how your child walks) 
• Constipation or urinary retention 

How is it diagnosed? 

CT scans can identify abnormal structures and their location. However, an MRI scan is necessary to help identify the type of fluid in the cyst.  

What are the treatments if my child develops symptoms? 

Most arachnoid cysts do not require treatment, but treatment may be needed if the cyst is causing symptoms. The goal of treatment is to drain the CSF fluid to relieve pressure on the brain or spine. This may be done by: 

• Creating an opening in the skull (craniotomy) or spine and making an opening in the cyst wall (fenestration) or removal of the cyst 
• Placement of a shunt (hollow tube in the brain) that drains fluid from the cyst into another area of the body 

When should I call the clinic? 

Call the clinic if any of the symptoms listed above are occurring, or with any questions or concerns.

What else do I need to know? 

• No specific activity restrictions are required. 
• If your child experiences a head injury, watch closely for severe headaches, vomiting, lethargy or seizure activity, and go to the emergency room if any of those symptoms occur.  
• Follow up with your neurosurgeon as recommended. 

Questions? 

This information is not specific to your child but provides general information. If you have any questions, please call your clinic. 

Reviewed 9/23

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