Arachnoid cyst

The most common type of cyst on the brain and a congenital disorder that may never produce any symptoms, but sometimes leads to problems in later life.

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What are arachnoid cysts?

Arachnoid cysts are membranes filled with cerebrospinal fluid (CSF) that are located between the brain and the arachnoid membrane (one of the layers of the membrane encasing the brain and spinal cord). They are usually present from birth and most do not cause symptoms.

Need to know

The symptoms associated with an arachnoid cyst vary depending on its location and size. Many cysts are completely asymptomatic.

If the cyst is symptomatic, it can cause neurological problems related to its location.

Your consultant will speak to you about your medical history and perform a physical examination. You may also need to undergo one, or both, of the following tests to confirm a diagnosis:

  • MRI scan. During an MRI scan, a magnetic field is used to create cross-sectional images of your brain. These images show the brain and spinal cord in very great detail.
  • CT scan. These use X-rays to show the bone of the skull and spine, which show up less well in MRI scans.

Treatment is generally recommended only when your cyst is symptomatic. In such cases, options may include:

  • Surgical placement of a cerebral shunt. This is a medical device that relieves pressure on your brain caused by an accumulation of fluid. One end is usually placed in the cyst, with the other end in the normal CSF.
  • Drainage of the cyst fluid by cutting a window in the membranes through a surgical operation.

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This content is intended for general information only and does not replace the need for personal advice from a qualified health professional.