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Arachnoid Cysts

Arachnoid cysts are cerebrospinal fluid-filled sacs 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 and develop as a result of head injury, meningitis, or tumors, or as a complication of brain surgery. The majority of 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 individuals 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. Males are four times more likely to have arachnoid cysts than females.

Typical symptoms of an arachnoid cyst around the brain include:

  • Headache

  • Nausea and vomiting

  • Hydrocephalus (accumulation of fluid in the brain, which can change the shape of an infant’s head)

  • Developmental delay

  • Behavioral changes

  • Seizures

  • Hearing and visual disturbances

  • Vertigo

  • Difficulties with balance and walking

  • Headaches

  • Seizures

  • Decreased cognitive performance

  • Hemiparesis (weakness or paralysis on one side of the body)

  • Ataxia (lack of muscle control)

Arachnoid cysts around the spinal cord compress the spinal cord or nerve roots and cause symptoms such as:

  • Back and leg pain

  • Tingling or numbness in the legs or arms

An arachnoid cyst that causes any of these symptoms needs to be evaluated for possible treatment, as it may continue to grow and cause neurological damage as it puts pressure on surrounding brain tissue. Since many of these symptoms can be caused by a range of other conditions, an accurate diagnosis is critical.


The need for treatment depends mostly upon the location and size of the cyst. If the cyst is small, not disturbing surrounding tissue, and not causing symptoms, some doctors will refrain from treatment.

In the past, doctors placed shunts in the cyst to drain its fluid. Now with microneurosurgical techniques and endoscopic tools that allow for minimally invasive surgery, more doctors are opting to surgically remove the membranes of the cyst or open the cyst so its fluid can drain into the cerebrospinal fluid and be absorbed.

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Content provided by the ​The National Institute of Neurological Disorders and Stroke (NINDS)

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