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Disease Profile

Arachnoid cysts

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Arachnoid cysts, intracranial; Intracranial arachnoid cysts


Congenital and Genetic Diseases; Endocrine Diseases; Nervous System Diseases


Arachnoid cysts are sacs filled with cerebrospinal fluid (CSF) 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. Arachnoid cysts can be primary or secondary. Primary arachnoid cysts are congenital (present at birth), resulting from abnormal development of the brain and spinal cord during early pregnancy. Secondary arachnoid cysts are less common, and result from head injuries, meningitis, tumors, or as a complication of brain surgery. Signs and symptoms depend on the location and size of the cyst and may include headache, nausea and vomiting, seizures, hearing and visual disturbances, vertigo, and difficulties with balance and walking. Although many affected individuals develop symptoms in the first year of life, some never develop symptoms. Whether and how to treat the condition depends on the location and size of the cyst. In some cases, arachnoid cysts are part of a genetic syndrome such as Chudley-McCullough syndrome, mucopolysaccharidosis, or Marfan syndrome, where there are many other associated signs and symptoms.[1][2] When treatment is recommended, it may include placing a shunt to drain the fluid; surgically removing the cyst membranes; or opening the cyst so the fluid can drain into the CSF.[3][4]


In some cases, arachnoid cysts do not cause any symptoms.[3] The location and size of the cyst in each individual determine whether symptoms occur, as well as when they might begin. Most individuals develop symptoms before age 20, and especially during the first year of life.[3][4] 

Signs and symptoms of arachnoid cysts vary depending on where are they located around the brain, and may include:[3][4]

  • Headache
  • Nausea
  • Vomiting
  • Seizures
  • Hearing and visual disturbances
  • Vertigo
  • Difficulties with balance and walking

Other symptoms may include:

  • Accumulation of excessive cerebrospinal fluid in the brain (hydrocephalus), resulting in increased intracranial pressure
  • Malformation of certain cranial bones, resulting in macrocephaly, which is an abnormally enlarged head (only in rare cases)
  • Neurological signs such as developmental delays, behavioral changes, inability to control voluntary movements (ataxia), difficulties with balance and walking, cognitive impairment, and weakness or paralysis on one side of the body (hemiparesis)

Arachnoids cysts located around the spinal cord can compress the spinal cord or nerve roots and may cause symptoms such as progressive back and leg pain, and/or tingling or numbness in the legs or arms and weakness. In some cases may cause other problems such as unwanted passage of urine or stool, called urinary or fecal incontinence.[3][4][5]

If left untreated, injuries in the brain or spinal cord may occur due to a progressive expansion of the cyst(s) or bleeding into the cyst.[4]

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
Percent of people who have these symptoms is not available through HPO
Arachnoid cyst
Fluid-filled sac located in membrane surrounding brain or spinal cord
Autosomal recessive inheritance
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific

[ more ]

Increased size of skull
Large head
Large head circumference

[ more ]

Abnormally small skull
Decreased circumference of cranium
Decreased size of skull
Reduced head circumference
Small head circumference

[ more ]



The exact underlying cause of arachnoid cysts is unknown.[3] Primary arachnoid cysts, which are congenital (present at birth), are due to developmental abnormalities of the brain and spinal cord during the early fetal period. Secondary arachnoid cysts, which occur more rarely, are associated with head injury, hemorrhage, meningitis, tumors, or a complication of brain surgery.[4][6] In some cases, arachnoid cysts are part of a genetic syndrome such as Chudley-McCullough syndrome, mucopolysaccharidosis, or Marfan syndrome, where there are many other associated signs and symptoms, related to the specific syndrome.[1][2]


Whether to treat all arachnoid cysts, as well as the method of treatment, has been a subject of controversy in the medical literature. The need for treatment depends mostly upon the location and size of the cyst, as well as whether symptoms are present. Some believe that treatment should be reserved for individuals with symptoms, while others believe that even asymptomatic cysts should be treated to avoid future complications.[6] In the past, doctors have placed shunts in the cyst in order to drain the fluid. However, now that specialized techniques and tools allow for minimally invasive surgery, more doctors are now 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.[4]

Learn more

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

In-Depth Information

  • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Arachnoid cysts. Click on the link to view a sample search on this topic.


  1. Khan AN. Arachnoid Cyst Imaging. Medscape Reference. January 5, 2016; https://emedicine.medscape.com/article/336489-overview.
  2. Zafeiriou DI & Batzios SP. Brain and Spinal MR Imaging Findings in Mucopolysaccharidoses: A Review. American Journal of Neuroradiology. January 2013; 34(1):5-13. https://www.ajnr.org/content/34/1/5.
  3. Arachnoid Cysts. National Organization for Rare Disorders (NORD). 2015; https://rarediseases.org/rare-diseases/arachnoid-cysts/.
  4. NINDS Arachnoid Cysts Information Page. NINDS. 03/27/2020; https://www.ninds.nih.gov/Disorders/All-Disorders/Arachnoid-Cysts-Information-Page#disorders-r1.
  5. Petridis AK, Doukas A, Barth H & Mehdorn HM. Spinal cord compression caused by idiopathic intradural arachnoid cysts of the spine: review of the literature and illustrated case. European Spine Journal. 2010; 19(2):124-129. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2899629/.
  6. Khan AN, Turnbull I, Al-Okaili R, MacDonald S & Mahmood K. Arachnoid Cyst. Medscape Reference. January 5, 2016; https://emedicine.medscape.com/article/336489-overview.
  7. Arachnoid cyst. Orphanet. Arpil 2005; https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=2356.
  8. Cassandra L. Kniffin. Arachnoid Cysts, Intracranial. Online Mendelian Inheritance in Man (OMIM). December, 2007; https://omim.org/entry/207790.
  9. Hong JC, Kim MS, Chang CH & Kim SH. Arachnoid cyst with spontaneous intracystic hemorrhage and chronic subdural hematoma. J Korean Neurosurg Soc. 2008; 43(1):54-56. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2588155/.
  10. Chen CP, Su YN, Weng SL, Tsai FJ, Chen CY, Liu YP, Chern SR, Chen WL, Wu PC, & Wang W.. Rapid aneuploidy diagnosis of trisomy 18 by array comparative genomic hybridization using uncultured amniocytes in a pregnancy with fetal arachnoid cyst detected in late second trimester. Taiwan J Obstet Gynecol. September 2012; 51(3):481-484. https://www.ncbi.nlm.nih.gov/pubmed/23040946.

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