What Are Arachnoid Cysts?



This site focuses on Arachnoid Cysts in the brain, but they can also be found on the spine.

What are arachnoid cysts?

Arachnoid cysts are cerebrospinal fluid covered by arachnoidal cells and collagen that may develop between the surface of the brain and the cranial base or on the arachnoid membrane, one of the 3 meningeal layers that cover the brain and the spinal cord. (Wiki)

Arachnoid cysts are fluid-filled sacs that occur on the arachnoid membrane that covers the brain (intracranial) and the spinal cord (spinal). There are three membranes covering these parts of the central nervous system: the dura mater, arachnoid, and pia mater. Arachnoid cysts appear on the arachnoid membrane, and they may also expand into the space between the pia mater and arachnoid membranes (subarachnoid space). The most common locations for intracranial arachnoid cysts are the middle fossa (near the temporal lobe), the suprasellar region (near the third ventricle) and the posterior fossa, which contains the cerebellum, pons, and medulla oblongata. (NORD)

More information on subarachnoid cysts and arachnoid cyst symptoms can be found on this website.



Some arachnoid cysts cause no symptoms at all. When an arachnoid cyst does cause symptoms, those symptoms depend on where the cyst is located.  When it’s located around the brain, symptoms 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 good news is that the prognosis for those with arachnoid cysts is excellent, and the surgery to drain or remove a cyst is safe and effective (WeillCornelBrainandSpine)



It is worth acknowledging most arachnoid cysts do not require any treatment. Current NHS guidelines follow a 'watch and wait' process, where people have regular MRI scans to access the cyst growth.

It is also worth noting most leading neurologists and neurosurgeons believe all arachnoid cysts, except incredibly large ones, to be asymptomatic. Many people with arachnoid cysts would refute this.

According to the UK Health centre, if any symptoms show, your cyst will need to be surgically drained, as if you ignore the problem, your vision may well be damaged as well. Therefore, if your arachnoid cyst is small, generally it will not require surgery. Of course, if the cyst expands then surgery will be required. Surgery could involve a couple of methods: needle aspiration can be used to drain the cyst; however this method could see the cyst return again. Alternatively, riskier method is through neurosurgery to drain the cyst; this could lead to scarring, and your whole arachnoid membrane may need to be taken out.  Either way, the surgery could well be risky, but it is worth remembering that it is better for the problem to be resolved than to let it fester; that way, your cyst could cause even more significant damage. (UK Health Centre)