Arachnoid Cysts

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What are arachnoid cysts?

Arachnoid cysts are sacs filled with spinal fluid that are located between the brain or spinal cord and the arachnoid membrane, one of the three membranes that cover the brain and spinal cord.   

  • Primary arachnoid cysts are present at birth and are the result of developmental abnormalities in the brain and spinal cord that arise during the early weeks of gestation.  
  • Secondary arachnoid cysts are not as common as primary cysts; they develop as a result of head injury, meningitis, or tumors, or as a complication of brain surgery. 

Most arachnoid cysts form outside the temporal lobe of the brain in an area of the skull known as the middle cranial fossa. Arachnoid cysts involving the spinal cord are rarer. The location and size of the cyst determine the symptoms and when those symptoms begin.   


Most people with arachnoid cysts develop symptoms before the age of 20, and especially during the first year of life, but some people with arachnoid cysts never have symptoms. Typical symptoms of an arachnoid cyst around the brain include:

  • Headache
  • Nausea and vomiting
  • Seizures
  • Hearing and visual disturbances
  • Vertigo
  • Difficulties with balance and walking

Arachnoid cysts around the spinal cord press parts of the spinal cord, or nerve roots, closer together. This causes symptoms such as back and leg pain and tingling or numbness in the legs or arms.

If arachnoid cysts are not treated, they may cause serious, permanent nerve damage if the cyst(s) injures the brain or spinal cord. This can happen if the cyst(s) get larger or if there is bleeding into the cyst. Treating the symptoms of arachnoid cysts usually makes the symptoms go away or improve.

Who is more likely to get arachnoid cysts?

Males are four times more likely to have arachnoid cysts than females. 

How are arachnoid cysts diagnosed and treated?

Diagnosing arachnoid cysts

Diagnosis usually involves a brain scan or spine scan using diffusion-weighted MRI (magnetic resonance imaging) which helps distinguish fluid-filled arachnoid cysts from other types of cysts.

Treating arachnoid cysts

The need for treatment depends mostly on the location and size of the cyst. If the cyst is small, it does not disturb surrounding tissue, and is not causing symptoms, some doctors will decide not to treat it.

Modern techniques and tools allow for surgery that is less invasive (in other words, surgery that involves using smaller cuts and fewer stitches). So, more doctors are choosing to remove the membranes of the cyst with surgery, or to open the cyst so its fluid can drain into the spinal fluid and be absorbed.  

Learn About Clinical Trials
Clinical trials are studies that allow us to learn more about disorders and improve care. They can help connect patients with new and upcoming treatment options.

How can I or my loved one help improve care for people with arachnoid cysts?

Consider participating in a clinical trial so clinicians and scientists can learn more about arachnoid cysts and related disorders. Clinical research uses human volunteers to help researchers learn more about a disorder and perhaps find better ways to safely detect, treat, or prevent disease.

All types of volunteers are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races, and ethnicities to ensure that study results apply to as many people as possible, and that treatments will be safe and effective for everyone who will use them.

For information about participating in clinical research visit NIH Clinical Research Trials and You. Learn about clinical trials currently looking for people with arachnoid cysts at

Where can I find more information about arachnoid cysts?

The following organization may help:

National Organization on Rare Disorders (NORD)
Phone: 203-744-0100 or 800-999-6673; 844-259-7178 Spanish

Order publications from the NINDS Catalog
The NINDS Publication Catalog offers printed materials on neurological disorders for patients, health professionals, and the general public. All materials are free of charge, and a downloadable PDF version is also available for most publications.