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Arachnoid Cyst: Causes, Symptoms, Tests to Diagnose

What is Arachnoid Cyst?

An arachnoid cyst is a type of cyst formation that is known to occur in brain and sometimes on the surrounding of spinal cord. In case of brain, the arachnoid cyst forms between the arachnoid membrane and the brain and in the case of spine the arachnoid cyst is formed between arachnoid membrane and spinal column. Thus it is called arachnoid cyst.

Arachnoid membrane is one of three membranes that surround the brain. Inside the cyst, there is accumulation of cerebrospinal fluid (CSF) which is the same fluid which protects the brain from the shocks and is found in the space between brain and skull. The walls of arachnoid cyst act like a wall and do not allow CSF (cerebrospinal fluid) to flow back to the CSF (cerebrospinal fluid) system causing accumulation of CSF (cerebrospinal fluid) inside arachnoid cyst.

Arachnoid cysts are classified into two categories: primary arachnoid cysts and secondary arachnoid cysts. Primary arachnoid cysts are found in children and generally they are congenital i.e. present from birth but not necessarily hereditary. The secondary arachnoid cysts are found in adults as they grow older. There are usually more cases of primary arachnoid cysts as compared to the secondary arachnoid cysts. Studies reveal that men are more prone to arachnoid cysts than female.

What is Arachnoid Cyst?

Arachnoid Cyst in Children

In case of children the occurrence of arachnoid cysts is by birth i.e. congenital. Usually the arachnoid cyst formation in children occurs due to any type of abnormality related to development of brain and spinal cord that may happen while the child is in the mother’s womb.

A very small fraction of children may develop arachnoid cysts due to some head injury. A few children, who undergo complex head surgery or develop tumors, meningitis etc… are also prone to cysts formation. All such cases are categorized as secondary cysts formation as they are not present from the birth. The cases of secondary cysts formation in children are very less as compared to primary arachnoid cysts.

Can I Pass the Condition of Arachnoid Cyst on to My Children?

Some of the latest studies reveal that arachnoid cyst may have genetic origin in some cases. According to a clinical study conducted on twins, arachnoid cysts my form if both the copies of a gene acquired from the parents are affected which is called “autosomal recessive” pattern in biological terms.

Classification of Arachnoid Cyst

Arachnoid cyst occurs either in the brain or around the spine and is accordingly classified as intracranial arachnoid cysts and spinal arachnoid cysts. Intracranial arachnoid cysts refer to cysts formation in brain, around to the arachnoidal cistern whereas the spinal arachnoid cysts may be intradural, extradural or perineural and would show signs and symptoms that are associated with radiculopathy.

Arachnoid cysts are further classified into two categories: primary (congenital) and secondary (acquired) as observed in case of dogs, cats and human beings.

Arachnoid cysts are tough to detect or diagnose as they are very much asymptomatic i.e. present no signs of illness. Even those little symptoms that may occur are insidious symptoms, which would result in late diagnosis of arachnoid cysts.

Causes of Arachnoid Cyst

The actual causes leading to arachnoid cysts still remains a mystery. Some researchers have found that arachnoid cysts occurs due to the tearing or splitting of arachnoid membrane because of some unknown reasons which gets accumulated and results into arachnoid cysts development. Some medical literatures have reported some cases of arachnoid cysts in multiple members of a same family which suggests that genes of a person is also one of the factors which makes a person prone to arachnid cysts formation.

Arachnoid cysts formation particularly in middle fossa is generally associated with poor growth of the temporal lobe (hypoplasia). Poor growth also refers to compression of the temporal lobe. However it still remains an unsolved mystery as to how malformation of temporal lobe causes arachnoid cysts in middle fossa.

Minor head trauma in some cases can damage the arachnoid cyst and cause arachnoid cysts to get worse. Any damage to the arachnoid cyst will lead to the leakage of the fluid inside and occupy the subarachnoid space. In some cases the situation of subarachnoid hemorrhage may arise as the tearing of blood vessels will cause the blood to rush into the arachnoid cyst. Even if the blood vessels lie on the outer side of arachnoid cyst, the leakage of blood can still cause hematoma. In both the cases of subarachnoid hemorrhage and hematoma, the rush of blood will cause the pressure inside the cranium to go up and suck the fluids out of nerve tissue forcing them to compress.

In some cases simple disorders like arachnoiditis, marfan’s syndrome, agenesis of the corpus callosum etc… can get worse and take the form of arachnoid cysts.

Symptoms of Arachnoid Cyst

The higher percentage of cases of arachnoid cysts come from the birth but may not show any symptoms during the whole lifetime of an individual as it is asymptomatic in nature. In very few cases there are other reasons like tumor inside brain, some head injury, any type of surgery or infection in brain etc… that may lead to arachnoid cyst.

However, the occurrence of the symptoms is also associated with the size of arachnoid cyst and also to the particular location of the arachnoid cyst. As the size of the arachnoid cyst gets larger, you are more likely to feel the symptoms because the arachnoid cyst starts to push against its surrounding part of brain, nerve and spinal cord.

In majority of the cases of arachnoid cysts, an individual shows the symptoms during the early stages of his life during childhood. The symptoms are not very specific and it is not necessary that every individual will show the symptoms which are discussed further.

Most people suffering from arachnoid cysts would show one or more of the following symptoms: dizziness, headaches, vomiting, nausea and high pressure inside cranial region due to the accumulation of CSF in brain also called hydrocephalus. In some cases, the arachnoid cyst formation can cause the cranial bones to grow abnormally resulting in enlarged head (macrocephaly).

There are some more specific symptoms, which are related to the size of the cyst and the portion where it develops. If there is a cyst in the middle fossa, an individual would show one or more of the following symptoms: abnormalities in vision and hearing, lethargy, seizures etc. The arachnoid cysts push against the surrounding part of brain and may cause neurological problems like changes in behavior, unable to walk and balance the body properly, retarded growth, feeble growth or paralysis of one side of the body, inability to control voluntary movements (ataxia) etc.

If there is arachnoid cyst formation in suprasellar region, one may show one or more of the following symptoms: vision problems, frequently shaking head, improper release of hormones which controls parameters like metabolic activities, sexual growth and development, normal growth etc.

Arachnoid cysts can also occur close to spine called as spinal arachnoid cysts but there are lesser cases of spinal arachnoid cysts as compared to intracranial arachnoid cysts. Generally a person having spinal arachnoid cysts may suffer from tingling or numbness in the hands or feet , infection in urinary tract, pain in the back, weaker legs, abnormal side-to-side curvature of the spine (scoliosis), uncomfortable leg movements due to involuntary muscle spasms (spasticity) etc. In extreme cases, spinal arachnoid cyst may also cause leg to completely paralyze.

There are some more findings, which report some more symptoms like headache and migraine, unable to concentrate, unable to express or understand language (aphasia). Other symptoms as well as physical findings included are of arachnoid cysts as well as attention-deficit disorder, migraine headaches and difficulties understanding or expressing language (aphasia). However, such findings are unable to explain the cause of these symptoms.

Following is the list of some common symptoms of arachnoid cyst located in the brain:

  • Vomiting, dizziness, balance issues are common symptoms of arachnoid cyst of the brain.
  • Nausea
  • Headache
  • Problems hearing, seeing or walking.
  • Seizures
  • Lethargy
  • Neurological problems are also seen in arachnoid cyst of the brain.

Following the common symptoms associated with the spinal arachnoid cyst formation:

  • Problems controlling the bladder and bowels are symptoms of arachnoid cyst of spine.
  • Muscle weakness or lack of feeling or tingling in the arms or legs is also seen in arachnoid cyst of spine.
  • Scoliosis
  • Back pain
  • Spasms.

Tests to Diagnose Arachnoid Cyst

Mostly the arachnoid cysts are detected during the examination with seizures for some other neurological issues. A professional doctor can suspect the occurrence of arachnoid cyst on the basis of the complete patient history and with the help of some simple clinical examinations and specially designed tests involving computed tomography (CT scan) and magnetic resonance imaging commonly known as MRI (Magnetic resonance imaging).

MRI and CT scan (Computerized (or computed) tomography) are the best possible tests to confirm the presence of any arachnoid cysts. CT scanning is an advanced engineering technique that creates a detailed cross-sectional image of full brain tissues using X-rays. On the other hand, MRI creates the same cross sectional images using radio waves and magnetic fields.


  1. Samadian, M., & Emami, S. (2014). Pediatric arachnoid cyst: a retrospective study. Journal of Neurosciences in Rural Practice, 5(Suppl 1), S18-S21. doi:10.4103/0976-3147.145219
  2. Marti, A. N., & Fuentes, R. A. (2021). Congenital intracranial arachnoid cysts: case series. International Journal of Surgery Case Reports, 83, 106067. doi:10.1016/j.ijscr.2021.106067
  3. Mayo Clinic. (2021). Arachnoid Cyst. https://www.mayoclinic.org/diseases-conditions/arachnoid-cysts/symptoms-causes/syc-20454690
  4. National Institute of Neurological Disorders and Stroke. (2021). Arachnoid Cysts Information Page. https://www.ninds.nih.gov/Disorders/All-Disorders/Arachnoid-Cysts-Information-Page
  5. Cleveland Clinic. (2021). Arachnoid Cysts. https://my.clevelandclinic.org/health/diseases/17840-arachnoid-cysts

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Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:August 3, 2023

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