Arachnoid cyst

Definition

Arachnoid cysts are sacs that are filled with cerebrospinal fluid and form in the surface region of the brain around the cranial base, or on the arachnoid membrane (one of three membranes that covers the brain and spinal cord).

Description

An arachnoid cyst forms when the two lipid (fatty) layers of the arachnoid membrane split apart to form a cavity. Like most membranes, the arachnoid membrane is comprised of two layers (leaflets) of lipid molecules. The hydrophilic (water attracting) region of the lipids is oriented towards an environment rich in water. The hydrophobic (water repelling) portion of the lipids will spontaneously partition away from water, in the interior of the membrane. When an arachnoid cyst forms, the two leaflets of the membrane split apart. Cerebrospinal fluid then fills the cavity.

Arachnoid cysts can be classified according to their location and by the type of tissue making up the cyst wall (arachnoid connective tissue or glioependymal tissue). Cysts that are found in the area of the cerebrum and in the spinal cord tend to be composed of arachnoid tissue, while cysts found in the supracollicular or retrocerebellar regions of the brain tend to be composed of either arachnoid connective tissue or glioependymal tissue.

The expansion of arachnoid cysts may occur when pulses of cerebrospinal fluid become trapped in the cyst cavity. The increasing volume of fluid causes the cyst to grow in size. However, the exact nature of cyst growth is not yet well understood. Arachnoid cysts tend to form on the left side of the brain, where the spinal canal intersects. Typically, a cyst makes up about one percent of the mass of the brain. Arachnoid cysts are also known as intracranial cysts.

Demographics

Infants are most susceptible to developing arachnoid cysts, although cyst formation can occur up through adolescence. Arachnoid cyst development in adults occurs much less frequently. Arachnoid cysts occur predominantly in males. The ratio of affected males to females is 4:1. The true rate of occurrence of arachnoid cysts is unknown, as many people with the disorder do not develop symptoms and the cyst remains undiagnosed.

Causes and symptoms

Arachnoid cysts arise mainly because of an abnormality occurring in development, sometimes as a result of a neonatal (newborn) infection. Other cysts are congenital (present at birth) and presumably result from abnormal formation of the subarachnoid space during embryological development. Cysts can also result from tumors, and complications of surgery or trauma (bleeding).

The symptoms of an arachnoid cyst are related to the size of the cyst and its location. For example, a small cyst may not cause any symptoms at all, and can be discovered accidentally during an unrelated examination. Large cysts can cause the head to change shape or to become enlarged (a phenomenon called macrocephaly). Symptoms associated with a larger cyst include headaches, seizures, accumulation of a pronounced amount of cerebrospinal fluid (hydrocephalus), increased pressure inside the cranial cavity, delay in mental and physical development, and altered behavior.

Other symptoms can include weakness or complete paralysis along one side of the body (hemiparesis), and the loss of control of muscles (ataxia).

Diagnosis

Arachnoid cysts are most commonly diagnosed followed a complaint of headaches, disruption of vision, or delayed development in a child. Even then, the discovery of a cyst is often incidental to another examination. The cysts can also be visualized using computerized tomography (CT) scanning, magnetic resonance imaging (MRI), and cranial ultrasonography. Overall, MRI is the preferred diagnostic technique, although cranial ultrasonography is an especially useful technique for newborns.

Arachnoid cysts have also been documented in people who have maladies such as Cockayne syndrome and Menkes disease. However, it is unclear whether this association is typical (and so of diagnostic importance) or merely coincidental.

Treatment team

Treatment can involve medical specialists such as neurosurgeons, imaging technicians, as well as nursing and other care providers. Physical therapists are also often involved.

Treatment

Typically, treatment is for the symptoms caused by the presence of the cyst, rather than for the cyst itself. However, when symptoms warrant, surgery is performed to relieve symptoms of increased intracranial pressure caused by the accumulation of fluid within the arachnoid cyst. Often, a device (shunt) is implanted within the cyst that drains the fluid away from the cyst and into the ventricles of the brain, or into the peritoneum (abdominal space), thus relieving the pressure. An alternative surgery called endoscopic fenestration uses an endoscope (an operative tool with an attached camera) to cut a small hole in the cyst, allowing the fluid to escape into the normal cerebrospinal fluid pathway.

Recovery and rehabilitation

Recovery from either surgical treatment is usually rapid, with symptoms resolving quickly after the excess fluid is redirected, assuming no permanent neurological damage occurred prior to treatment. An active infant or young child often wears a protective helmet during the recovery phase. Physical and mental developmental milestones are usually monitored for infants and children. Follow-up monitoring of the implanted shunt and overall assessment of the cyst are normally required.

Clinical trials

As of January 2004, the National Institute of Neurological Diseases and Stroke (NINDS) was recruiting patients for a study of syringomyelia. The malady arises when cerebrospinal fluid is blocked from its normal circulation, as by an arachnoid cyst. As well, NINDS and other agencies support research that seeks to understand the basis of arachnoid cyst formation.

Prognosis

While many arachnoid cysts cause no symptoms and require no treatment, others, if left untreated, can grow and cause pressure or severe bleeding within the brain (hemorrhage). The result can be permanent neurological damage. However, with treatment, the outlook for most persons with an arachnoid cyst is encouraging and permanent damage can be avoided.

Resources

BOOKS

Parker, J. N., and P. M. Parker. The Official Patient's Sourcebook on Arachnoid Cysts. A Revised and Updated Directory for the Internet Age. San Diego. Icon Health Publications, 2002.

OTHER

"Arachnoid Cysts Information Page." National Institute of Neurological Disorders and Stroke.http://www.ninds.nih.gov/health_and_medical/disorders/aracysts_doc.htm (January 30, 2004).

Khan, A. N. "Arachnoid Cyst." eMedicine.http://www.emedicine.com/radio/topic48.htm (January 30, 2004).

ORGANIZATIONS

National Institute for Neurological Diseases and Stroke (NINDS). 6001 Executive Boulevard, Bethesda, MD 20892. (301) 496-5751 or (800) 352-9424. http://www.ninds.nih.gov.

National Organization for Rare Disorders. 55 Kenosia Avenue, Danbury, CT 06813-1968. (203) 744-0100 or (800) 999-6673; Fax: (203) 798-2291. orphan@rarediseases.org. http://www.rarediseases.org.

Brian Douglas Hoyle, Ph.D.

A fluid-filled cyst lined with arachnoid membrane, frequently situated in the sylvian fissure of the brain.

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (July 2007)

Arachnoid cyst
Classification and external resources
ICD-10	G93.0
ICD-9	348.0
OMIM	207790
DiseasesDB	33219
eMedicine	radio/48
MeSH	[3]

Arachnoid cysts are cerebrospinal fluid covered by arachnoidal cells and collagen^[1] that may develop between the surface of the brain and the cranial base or on the arachnoid membrane, one of the three membranes that cover the brain and the spinal cord.^[2] Arachnoid cysts are a congenital disorder,^[3] and most cases begin during infancy; however, onset may be delayed until adolescence.^[2]

Contents 1 Classification 2 Signs and symptoms 2.1 Location-specific symptoms 3 Causes 4 Diagnosis 5 Treatment/Management 6 Prognosis 7 Epidemiology 8 History 9 See also 10 References 11 External links

Classification

Arachnoid cysts can be found on the brain, or on the spine. Intracranial arachnoid cysts usually occur adjacent to the arachnoidal cistern.^[4] Spinal arachnoid cysts may be extradural, intradural, or perineural and tend to present with signs and symptoms indicative of a radiculopathy.^[4]

Arachnoid cysts can be relatively asymptomatic or present with insidious symptoms; for this reason, diagnosis is often delayed.

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 or location.

Symptoms vary by the size and location of the cyst(s), though small cysts usually have no symptoms and are discovered only incidentally.^[2] On the other hand, a number of symptoms may result from large cysts:

• Cranial deformation or macrocephaly (enlargement of the head), particularly in children^[5]
• Cysts in the suprasellar region in children have presented as bobbing and nodding of the head called Bobble-Head Doll Syndrome.^[5]
• Cysts in the left middle cranial fossa have been associated with ADHD in a study on affected children.^[6]
• Headaches.^[2] 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.^[7]
  • 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.^[8]
• Seizures^[2]
• Hydrocephalus (excessive accumulation of cerebrospinal fluid)^[2]
• Increased intracranial pressure^[2]
• Developmental delay^[2]
• Behavioral changes^[2]
• Hemiparesis (weakness or paralysis on one side of the body)^[2]
• Ataxia (lack of muscle control)^[2]
• Musical hallucination^[9]
• Pre-senile dementia,^[10] a condition often associated with Alzheimer's disease
• In elderly patients (>65 years old) symptoms were similar to chronic subdural hematoma or normal pressure hydrocephalus:^[11]
  • Dementia
  • Urinary incontinence
  • Hemiparesis
  • Headache
  • Seizures

Location-specific symptoms

The following list of location-specific symptoms should be interpreted in the context of what they represent: results from several independent, unrelated studies. As of September 2006^{[update][dated info]}, no published research comprehensively maps physical and neuropsychiatric symptoms to a specific arachnoid cyst location.^[10]

• A supratentorial arachnoid cyst can mimic a Ménière's disease attack.^[12]
• Frontal arachnoid cysts have been associated with depression.^[13]
• Cysts on the left temporal lobe have been associated with psychosisHowever this remains controversial and subjective to the individual clinician.^[14][15] A left fronto-temporal cyst more specifically showed symptoms of alexithymia.^[16]
• Cyst on the right sylvian fissure resulted in new onset of schizophrenia-like symptoms at age 61.^[17]
• A patient with a cyst on the left middle cranial fossa had auditory hallucinations, migraine-like headaches, and periodic paranoia^[8]
• Patients with left temporal lobe cysts had mood disturbances similar to manic depression (bipolar disorder)^[18]
• Most neurosurgeons remain skeptical on the correlation between arachnoid cyst and mental illness and consider the two unrelated or incidental.

This section requires expansion.

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 exact role that temporal lobe abnormalities play in the development of middle fossa arachnoid cysts is unknown.

There are some cases where hereditary disorders have been connected with arachnoid cysts.^[19]

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), 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.

Arachnoid cysts can also occur secondary to other disorders such as Marfan syndrome, arachnoiditis, or agenesis of the corpus callosum.

Diagnosis

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.^[10] Myelograms are contraindicated for people with arachnoid cysts.

This section requires expansion.

Treatment/Management

Treatment for arachnoid cysts occurs when symptoms present themselves.^[2] A variety of procedures may be used to decompress (remove pressure from) the cyst.

• Surgical placement of a cerebral shunt:^[20]
  • An internal shunt drains into the subdural compartment.^[21]
  • A cystoperitoneal shunt drains to the peritoneal cavity.^[22]
• Fenestration:
  • Craniotomy with excision^[23]
  • Various endoscopic techniques are proving effective,^[24] including laser-assisted techniques.^[25]
• Drainage by needle aspiration or burr hole.
• Capsular resection^[11]
• Pharmacological treatments may address specific symptoms such as seizures or pain.

A 1994 study found surgery necessary for good outcome in patients >65 years old when the cysts began displaying symptoms.^[26]

This section requires expansion.

Prognosis

Untreated, arachnoid cysts may cause permanent severe neurological damage due to the progressive expansion of the cyst(s) or hemorrhage (bleeding).^[2] However, with treatment most individuals with arachnoid cysts do well.

More specific prognoses are listed below:

• Patients with impaired preoperative cognition had postoperative improvement after surgical decompression of the cyst.^[27][28]
• Surgery can resolve psychiatric manifestations in selected cases.^[29]

Epidemiology

Arachnoid cysts are seen in 4% of the population.^[30] Only 20% of these have symptoms, usually from secondary hydrocephalus.^[30]

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.^[31]

History

This section requires expansion.

See also

• Acoustic Neuroma
• Arachnoiditis
• Brain Tumors, General
• Dandy-Walker syndrome
• Empty Sella Syndrome
• Porencephaly
• Syringomyelia
• Hyperprolactinemia
• Panhypopituitarism
• Arnold-Chiari Malformation

References

1. ^ Ariai S, Koerbel A, Bornemann A, Morgala M, Tatagiba M. "Cerebellopontine angle arachnoid cyst harbouring ectopic neuroglia", Pediatr Neurosurg. 2005 Jul-Aug;41(4):220-3. (PMID 16088260)
2. ^ ^{a b c d e f g h i j k l m} http://www.ninds.nih.gov/disorders/arachnoid_cysts/arachnoid_cysts.htm NINDS Arachnoid Cysts Information Page
3. ^ Gelabert-Gonzalez M. "Intracranial arachnoid cysts", Rev Neurol., 2004 Dec 16-31;39(12):1161-6. (PMID 15625636)
4. ^ ^{a b} 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
5. ^ ^{a b} Barker RA, Scolding N, Rowe D, Larner AJ. The A-Z of Neurological Practice: A Guide to Clinical Neurology Cambridge University Press 2005 Jan 10, p61. (ISBN 0-521-62960-8)
6. ^ Millichap JG. "Temporal lobe arachnoid cyst-attention deficit disorder syndrome: role of the electroencephalogram in diagnosis", Neurology 1997 May;48(5):1435-9. (PMID 9153486)
7. ^ Valença MM, Valença LP, Menezes TL. "Computed tomography scan of the head in patients with migraine or tension-type headache", Arq Neuropsiquiatr. 2002 Sep;60(3-A):542-7. (PMID 12244387)
8. ^ ^{a b} 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
9. ^ Griffiths TD. "Musical hallucinosis in acquired deafness. Phenomenology and brain substrate.", Brain, 2000 Oct;123 ( Pt 10):2065-76. (PMID 11004124)
10. ^ ^{a b c} 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
11. ^ ^{a b} Yamakawa H, Ohkuma A, Hattori T, Niikawa S, Kobayashi H. "Primary intracranial arachnoid cyst in the elderly: a survey on 39 cases", Acta Neurochir (Wien). 1991;113(1-2):42-7. (PMID 1799142)
12. ^ Buongiorno G, Ricca G. "Supratentorial arachnoid cyst mimicking a Ménière's disease attack", J Laryngol Otol. 2003 Sep;117(9):728-30. (PMID 14561365)
13. ^ Cummings JL, Mega MS. Neuropsychiatry and Behavioral Neuroscience, Oxford University Press, USA; 2Rev Ed, 2003 Jan 23;208. (ISBN 0-19-513858-9)
14. ^ Alves da Silva J, Alves A, Talina M, Carreiro S, Guimarães J, Xavier M. "Arachnoid cyst in a patient with psychosis: a case report" Annals of General Psychiatry 2007, 6:16) [1]
15. ^ Vakis AF, Koutentakis DI, Karabetsos DA, Kalostos GN. "Psychosis-like syndrome associated with intermittent intracranial hypertension caused by a large arachnoid cyst of the left temporal lobe", Br J Neurosurg. 2006 Jun;20(3):156-9. (PMID 16801049)
16. ^ Blackshaw S, Bowen RC. "A case of atypical psychosis associated with alexithymia and a left fronto-temporal lesion: possible correlations", Can J Psychiatry 1987 Nov;32(8):688-92. (PMID 3690485)
17. ^ Cullum CM, Heaton RK, Harris MJ, Jeste DV. "Neurobehavioral and neurodiagnostic aspects of late-onset psychosis", Arch Clin Neuropsychol. 1994 Oct;9(5):371-82. (PMID 14589653)
18. ^ Heinrichs, RW. In Search of Madness: Schizophrenia and Neuroscience Oxford University Press, USA (March 29, 2001); p129. (ISBN 0-19-512219-4)
19. ^ Schievink WI, Huston J 3rd, Torres VE, Marsh WR. "Intracranial cysts in autosomal dominant polycystic kidney disease" J Neurosurg 1995 Dec;83(6):1004-7. (PMID 7490613)
20. ^ Strojnik T. "Different approaches to surgical treatment of arachnoid cysts", Wiener Klinische Wochenschrift.[2] 2006;118 Suppl 2:85-8. (PMID 16817052)
21. ^ Helland CA, Wester K. "Arachnoid cysts in adults: long-term follow-up of patients treated with internal shunts to the subdural compartment", Surg Neurol. 2006 Jul;66(1):56-61; discussion 61. (PMID 16793443)
22. ^ Park SW, Yoon SH, Cho KH, Shin YS. "A large arachnoid cyst of the lateral ventricle extending from the supracerebellar cistern—case report", Surg Neurol 2006 Jun;65(6):611-14. (PMID 16720186)
23. ^ Gangemi M, Colella G, Magro F, Maiuri F. "Suprasellar arachnoid cysts: endoscopy versus microsurgical cyst excision and shunting", Br J Neurosurg 2007 Jun;21(3):276-80. (PMID 17612918)
24. ^ Greenfield JP, Souweidane MM. "Endoscopic management of intracranial cysts", Neurosurg Focus. 2005 Dec 15;19(6):E7. (PMID 16398484)
25. ^ Van Beijnum J, Hanlo PW, Han KS, Ludo Van der Pol W, Verdaasdonk RM, Van Nieuwenhuizen O. "Navigated laser-assisted endoscopic fenestration of a suprasellar arachnoid cyst in a 2-year-old child with bobble-head doll syndrome", J Neurosurg. 2006 May;104(5 Suppl):348-51. (PMID 16848093)
26. ^ Caruso R, Salvati M, Cervoni L. "Primary intracranial arachnoid cyst in the elderly", Neurosurg Rev. 1994;17(3):195-8. (PMID 7838397)
27. ^ Wester K, Hugdahl K. "Arachnoid cysts of the left temporal fossa: impaired preoperative cognition and postoperative improvement." J Neurol Neurosurg Psychiatry 1995 Sep;59(3):293-8. (PMID 7673959)
28. ^ Wester K. "Intracranial arachnoid cysts--do they impair mental functions?" J Neurol 2008 Aug;255(8):1113-20. (PMID 18677648)
29. ^ Kohn R, Lilly RB, Sokol MS, Malloy PF. "Psychiatric presentations of intracranial cysts", J Neuropsychiatry Clin Neurosci 1989; 1:60-66. (PMID 2577719)
30. ^ ^{a b} Flaherty AW. The Massachusetts General Hospital Handbook of Neurology 2000 Jan 1;105. (ISBN 0-683-30576-X)
31. ^ Weber F, Knopf H. "Incidental findings in magnetic resonance imaging of the brains of healthy young men", J Neurol Sci. 2006 Jan 15;240(1-2):81-4. Epub 2005 Oct 26. (PMID 16256141)

External links

• Patient support sites:

• The Arachnoid Cyst Website
• arachnoidcyst.org
• Arachnoid Activist

• Video of endoscopic fenestration procedure
• Video of MRI scan showing two arachnoid cysts

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