Arachnoid Cyst

Arachnoid Cyst


A cyst is a fluid-filled cavity. An arachnoid cyst is a fluid-containing sac that mostly occurs in the head though it can also occur in the spinal cord. In general, this cyst occurs in the central nervous system. Arachnoid membrane is one of the three membrane layers that envelop the brain and spinal cord. There is a space found between the brain and spinal column and the arachnoid membrane, this space is known as the arachnoid space. When a cyst occurs in this space, it is called an arachnoid cyst. When an arachnoid cyst forms in the head, it is usually located between the brain and skull in tiny collections around the brain called ventricles. The fluid contained in an arachnoid cyst is the cerebrospinal fluid (CSF), this fluid occurs naturally and serves to protect the brain and spinal column where it is typically found. An arachnoid cyst wall is not permeable and so the fluid cannot pass down to the CSF system thus this fluid keeps on accumulating. Arachnoid cysts are congenital in children or they are noticed at birth and this form is known as the primary arachnoid cysts. The secondary form of arachnoid cysts is those that occur much later in life. The primary form is more common than the secondary form.

Arachnoid cyst
Photo Credit: Epainassist


Most cases of arachnoid cysts are symptomless thus those who have it do not know that they do and it is usually picked up as an incidental finding (such as when the head is examined for other pathologies).

In some rare cases, arachnoid cysts may be symptomatic. These symptoms noticed are related to the site and size of the cyst. For example, a large arachnoid cyst may compress the nerves and vessels of the brain and spinal cord. When found in the brain, the possible symptoms that it can produce include:

When found in the spinal column, it presents with the following symptoms:

See a doctor if you notice these symptoms.


The primary form of the arachnoid cyst is usually due to an improper brain and spinal column growth in utero. The specific cause of this abnormal growth is not known but it might just be genetics.

The secondary form of anarachnoid cyst which is the type that develops much later in life is caused by the following:

  • Head injury
  • Spinal cord injury
  • Complications following a brain or spinal cord surgery
  • Infection of the brain meninges
  • Tumors

Arachnoid cysts occur frequently in children. There is a gender predilection with it occurring more in men than in women, this report is from the National Organization for Rare Disorders.


The tests the doctor will request if they think you have arachnoid cysts are imaging tests. A CT scan or an MRI is useful.


For an uncomplicated case of an arachnoid cyst, that is, the type without symptoms, it is best left untreated but it should be closely monitored for an increase in size or the presence of symptoms. If it starts being problematic then treatment should be sought.

For an asymptomatic case of an arachnoid cyst, it will most likely be drained by a doctor. There are two procedures that are usually advised to effect this drainage. In the first procedure, a tiny cut is made close to the cyst and an endoscope which has a camera at its distal part is put into this opening. The camera enables the visualization of the cyst and the surgical field. The endoscope is used to make an opening in the cyst so as to drain it into the CSF system, where it will be circulated around the body. This procedure is known as FENESTRATION. In the second procedure, a shunt is put into the cyst to redirect the fluid present to another body part such as the stomach.

A spinal column cyst with symptoms should be removed surgically but if it is not achievable, a fenestration or shunting can still be done to drain it.


Those with asymptomatic cyst are able to live normally even with the cyst left untreated. They are advised by the doctor to carry out regular checkups to monitor it for any new findings.

For a symptomatic cyst, drainage should clear the symptoms.

Very rarely, permanent neurological injury can result from an expanding arachnoid cyst that was left untreated.

Ask the doctor questions to get more comprehension on the subject matter including the options available for treatment and the long term outcome.

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