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Children's Hospital at Dartmouth Hitchcock (CHad)
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Arachnoid Cysts

An arachnoid cyst is a very common finding seen on brain imaging studies.

Arachnoid cysts are "pockets" in the clear, thin covering of the brain called the arachnoid. The fluid that normally surrounds the brain ("cerebrospinal fluid" or "CSF") can accumulate in these pockets and create an "arachnoid cyst."  These cysts are typically found on the outside of the brain and are thought to be present since birth. These can occur almost anywhere on the surface of the brain.

MRI scan showing arachnoid cyst (arrow) in the brain.

MRI scan showing arachnoid cyst (arrow) in the brain.


Although the symptoms can vary depending on where the cyst is, the most common symptoms are:

  • Headaches
  • Nausea or vomiting
  • Seizures
  • Large or unusual size of the head
  • Developmental delay
  • Weakness on one side of the body


Arachnoid cysts are usually discovered "incidentally" (or by accident) on imaging of the brain, such as computed tomography (CT or CAT scan) or magnetic resonance imaging (MRI) that was performed for a different reason, such as following a trauma. Sometimes further imaging, such as a more detailed MRI scan, is needed to make sure that the cyst is not a brain tumor.


When someone has no problems related to the arachnoid cyst, surgery is usually not recommended. Patients are usually seen back for follow-up and for repeat MRI studies to make sure the arachnoid cyst is not getting bigger or causing any problems that might require surgery.


Surgery is usually done on patients who have symptoms from compression of the brain by the cyst or if the cyst is getting larger on imaging studies.

The goal of surgery is to drain the fluid from the cyst. Surgical options include placing a catheter into the cyst and draining the cyst fluid into another body cavity ("shunting") or opening the cyst up directly and draining the fluid into the space surrounding the brain ("craniotomy for fenestration"). Your neurosurgeon will work with you to determine which option would be recommended for your child.

Surgery usually takes between 2 and 4 hours and children usually stay in the hospital for 2 to 4 days after the operation. Most children can resume regular activities, including school, approximately 2 weeks after surgery. High-risk activities, including contact sports, are usually restricted for 3 months after surgery.

Page reviewed on: Nov 19, 2009

Page reviewed by: Susan R. Durham, MD, MS

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