Arachnoid cysts are cerebrospinal fluid covered by arachnoidal cells and collagen that may develop between the surface of the

brain The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...

and the cranial base or on the arachnoid membrane, one of the three meningeal layers that cover the brain and the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spin ...

. Primary arachnoid cysts are a

congenital disorder A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities c ...

whereas secondary arachnoid cysts are the result of head injury or trauma. Most cases of primary cysts begin during infancy; however, onset may be delayed until adolescence.

Signs and symptoms

Patients with arachnoid cysts may never show symptoms, even in some cases where the cyst is large. Therefore, while the presence of symptoms may provoke further clinical investigation, symptoms independent of further data cannot—and should not—be interpreted as evidence of a cyst's existence, size, location, or potential functional impact on the patient. Symptoms vary by the size and location of the cyst(s), though small cysts usually have no symptoms and are discovered only incidentally. On the other hand, a number of symptoms may result from large cysts: * Cranial deformation or macrocephaly (enlargement of the head), particularly in childrenBarker RA, Scolding N, Rowe D, Larner AJ. ''The A-Z of Neurological Practice: A Guide to Clinical Neurology''

Cambridge University Press Cambridge University Press is the university press of the University of Cambridge. Granted letters patent by Henry VIII of England, King Henry VIII in 1534, it is the oldest university press in the world. It is also the King's Printer. Cambr ...

2005 Jan 10, p61. () * Cysts in the suprasellar region in children have presented as bobbing and nodding of the head called bobble-head doll syndrome. * Cysts in the left middle cranial fossa have been associated with ADHD in a study on affected children. *

Headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a resul ...

s. A patient experiencing a headache does not necessarily have an arachnoid cyst. ** In a 2002 study involving 78 patients with a migraine or tension-type headache, CT scans showed abnormalities in over a third of the patients, though arachnoid cysts only accounted for 2.6% of patients in this study. ** A study found 18% of patients with intracranial arachnoid cysts had non-specific headaches. The cyst was in the temporal location in 75% of these cases.Cameron AD. "Psychotic phenomena with migraine and an arachnoid cyst", ''Progress in Neurology and Psychiatry'' 2002 Mar-Apr 6(2
http://www.escriber.com/Progress/Features.asp? Action=View&Archive=True&ID=67&GroupID=&Page=11
*

Seizure An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with l ...

s *

Hydrocephalus Hydrocephalus is a condition in which an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased pressure inside the skull. Older people may have headaches, double vision, poor balance, urinary in ...

(excessive accumulation of cerebrospinal fluid) * Increased intracranial pressure * Developmental delay * Behavioral changes * Nausea * Dysdiadokinesis *

Hemiparesis Hemiparesis, or unilateral paresis, is weakness of one entire side of the body ('' hemi-'' means "half"). Hemiplegia is, in its most severe form, complete paralysis of half of the body. Hemiparesis and hemiplegia can be caused by different medi ...

(weakness or paralysis on one side of the body) *

Ataxia Ataxia is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in eye movements. Ataxia is a clinical manifestation indicating dysfunction of t ...

(lack of muscle control) * Musical

hallucination A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combinati ...

* Pre-senile

dementia Dementia is a disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively affe ...

,Richards G, Lusznat RM. "An arachnoid cyst in a patient with pre-senile dementia", ''Progress in Neurology and Psychiatry'', 2001 May–June;5(3
http://www.escriber.com/Progress/Features.asp? Action=View&Archive=True&ID=29&GroupID=&Page=18
a condition often associated with Alzheimer's disease * In elderly patients (>80 years old) symptoms were similar to chronic subdural hematoma or normal pressure

hydrocephalus Hydrocephalus is a condition in which an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased pressure inside the skull. Older people may have headaches, double vision, poor balance, urinary in ...

: ** Dementia **

Urinary incontinence Urinary incontinence (UI), also known as involuntary urination, is any uncontrolled leakage of urine. It is a common and distressing problem, which may have a large impact on quality of life. It has been identified as an important issue in geri ...

** Hemiparesis ** Headache ** Seizures

Location-specific symptoms

* A supratentorial arachnoid cyst can mimic a

Ménière's disease Ménière's disease (MD) is a disease of the inner ear that is characterized by potentially severe and incapacitating episodes of vertigo, tinnitus, hearing loss, and a feeling of fullness in the ear. Typically, only one ear is affected initi ...

attack. * Frontal arachnoid cysts have been associated with depression.Cummings JL, Mega MS. ''Neuropsychiatry and Behavioral Neuroscience'', Oxford University Press, USA; 2Rev Ed, 2003 Jan 23;208. () * Cysts on the left temporal lobe have been associated with

psychosis Psychosis is a condition of the mind that results in difficulties determining what is real and what is not real. Symptoms may include delusions and hallucinations, among other features. Additional symptoms are incoherent speech and behavior ...

. A left fronto-temporal cyst showed symptoms of alexithymia. * Cyst on the right sylvian fissure resulted in new onset of

schizophrenia Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social wi ...

-like symptoms at age 61. * A patient with a cyst on the left middle cranial fossa had auditory

hallucinations A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combinati ...

migraine Migraine (, ) is a common neurological disorder characterized by recurrent headaches. Typically, the associated headache affects one side of the head, is pulsating in nature, may be moderate to severe in intensity, and could last from a few ho ...

-like headaches, and periodic paranoia * Patients with left temporal lobe cysts had mood disturbances similar to manic depression (bipolar disorder) and were known to show outward aggression

Causes

The exact cause of arachnoid cysts is not known. Researchers believe that most cases of arachnoid cysts are developmental malformations that arise from the unexplained splitting or tearing of the arachnoid membrane. In some cases, arachnoid cysts occurring in the middle fossa are accompanied by underdevelopment ( hypoplasia) or compression of the

temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved in proc ...

. The exact role that temporal lobe abnormalities play in the development of

middle fossa The middle cranial fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest. It is bounded in front by the pos ...

arachnoid cysts is unknown. There are some cases where hereditary disorders have been connected with arachnoid cysts. Some complications of arachnoid cysts can occur when a cyst is damaged because of minor head trauma. Trauma can cause the fluid within a cyst to leak into other areas (e.g., subarachnoid space). Blood vessels on the surface of a cyst may tear and bleed into the cyst (intracystic

hemorrhage Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...

), increasing its size. If a blood vessel bleeds on the outside of a cyst, a collection of blood ( hematoma) may result. In the cases of intracystic hemorrhage and hematoma, the individual may have symptoms of increased pressure within the cranium and signs of compression of nearby nerve (neural) tissue. Some scientists debate whether arachnoid cysts are a true congenite condition or if this should be separated from secondary cysts. A recent study shows differences in communication between the arachnoid cyst and the subarachnoid space by CT cisternography. A comparison of arachnoid cyst fluid and CSF in a series of patients show differences in chemical composition. Arachnoid cysts can also occur secondary to other disorders such as Marfan syndrome, arachnoiditis, or agenesis of the corpus callosum.

Diagnosis

Temporale Arachnoidalzyste links CT axial

Diagnosis is principally by MRI. Frequently, arachnoid cysts are incidental findings on MRI scans performed for other clinical reasons. In practice, diagnosis of symptomatic arachnoid cysts requires symptoms to be present, and many with the disorder never develop symptoms. Additional clinical assessment tools that can be useful in evaluating a patient with arachnoid cysts include the mini-mental state examination (MMSE), a brief questionnaire-based test used to assess

cognition Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thoug ...

Classification

Arachnoid cysts can be found on the brain or on the spine. Intracranial arachnoid cysts usually occur adjacent to the arachnoidal cistern.Arachnoid cyst. (n.d.). Gale Encyclopedia of Neurological Disorders. Retrieved September 10, 2006, from Answers.com Web site: http://www.answers.com/topic/arachnoid-cyst Spinal arachnoid cysts may be extradural, intradural, or perineural and tend to present with signs and symptoms indicative of a radiculopathy. Arachnoid cysts may also be classified as primary (congenital) or secondary (acquired) and have been reported in humans, cats, and dogs. Arachnoid cysts can be relatively

asymptomatic In medicine, any disease is classified asymptomatic if a patient tests as carrier for a disease or infection but experiences no symptoms. Whenever a medical condition fails to show noticeable symptoms after a diagnosis it might be considered as ...

or present with insidious symptoms; for this reason, diagnosis is often delayed.

Treatment

Most arachnoid cysts are asymptomatic and do not require treatment. Treatment may be necessary when symptomatic. A variety of procedures may be used to decompress (remove pressure from) the cyst. * Surgical placement of a cerebral shunt: ** An internal shunt drains into the subdural compartment. ** A cystoperitoneal shunt drains to the peritoneal cavity. * Fenestration: ** Craniotomy with excision ** Various endoscopic techniques are proving effective, including laser-assisted techniques. * Drainage by needle aspiration or burr hole. * Capsular resection * Pharmacological treatments may address specific symptoms such as seizures or pain.

Prognosis

Most arachnoid cysts are asymptomatic, and do not require treatment. Where complications are present, leaving arachnoid cysts untreated may cause permanent severe neurological damage due to the progressive expansion of the cyst(s) or

(bleeding). However, with treatment most individuals with symptomatic arachnoid cysts do well. More specific prognoses are listed below: * Patients with impaired preoperative

had postoperative improvement after surgical decompression of the cyst. * Surgery can resolve psychiatric manifestations in selected cases.

Epidemiology

Arachnoid cysts are seen in up to 1.1% of the populationFlaherty AW. ''The Massachusetts General Hospital Handbook of Neurology'' 2000 Jan 1;105. () with a gender distribution of 2:1 male:female. Only 20% of these have symptoms, usually from secondary

. A study that looked at 2,536 healthy young males found a prevalence of 1.7% (95% CI 1.2 to 2.3%). Only a small percentage of the detected abnormalities require urgent medical attention.

References

External links

{{DEFAULTSORT:Arachnoid Cyst Congenital disorders Central nervous system disorders