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Arachnoid cyst
Classification & external resources

ICD-10	Q04.6
ICD-9	348.0
OMIM	207790
DiseasesDB	33219
eMedicine	radio/48
MeSH	D016080

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

Arachnoid cysts can be intracranial (in the cranium), or on the spine. Intracranial arachnoid cysts usually occur adjacent to 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]

The "Silent" disabilities Arachnoid Cysts can cause are due to a patient not being able to articulate their problems which leads to not getting treatment because a cyst is considered "asymptomatic" due to a lack of collective knowledge of what happens to patients as they degenerate, a lack of research and a largely ignorant medical community and their inabilities to understand advanced symptoms and can lead to problems such as developing strokes, Syringomyelia, Chiari Malformations, Arachnoiditis, Empty sella syndrome,^[5] and bone erosion which can destroy the architecture of the brain and allow further problems to occur.

Patients with arachnoid cysts may never show symptoms, even in some cases where the cyst is large.^{[citation needed]} Additionally, the symptoms experienced are not unique to this disease and can be masked by other problems such as Fibromyelgia, MS, and "migraines". 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 because only a CAT scan, MRI or PET scan can confirm the diagnosis

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^[6]
• Cysts in the suprasellar region in children have presented as bobbing and nodding of the head called Bobble-Head Doll Syndrome.^[6]
• Cysts in the left middle cranial fossa have been associated with ADHD in a study on affected children.^[7]
• Headaches.^[2] While the most common symptom,^{[citation needed]} 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.^[8]
  • 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.^[9]
• 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^[10]
• Pre-senile dementia,^[11] 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:^[12]
  • Dementia
  • Urinary incontinence
  • Hemiparesis
  • Headache
  • Seizures

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, no research has been published that comprehensively maps physical and neuropsychiatric symptoms to a specific arachnoid cyst location.^[11]

• A supratentorial arachnoid cyst can mimic a Ménière's disease attack.^[13]
• Frontal arachnoid cysts have been associated with depression.^[14]
• Cysts on the left temporal lobe have been associated with psychosis.^[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^[9]
• Patients with left temporal lobe cysts had mood disturbances similar to manic depression (bipolar disorder)^[18]

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. According to the medical literature, cases of arachnoid cysts have run in families (familial cases) suggesting that a genetic predisposition may play a role in the development of arachnoid cysts in some individuals.

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.

In a few rare cases, intracranial arachnoid cysts may be inherited as an autosomal recessive trait. In recessive disorders, the condition does not appear unless a person inherits the same defective gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk of transmitting the disease to the children of a couple, both of whom are carriers for a recessive disorder, is 25 percent. Fifty percent of their children risk being carriers of the disease, but generally will not show symptoms of the disorder. Twenty-five percent of their children may receive both normal genes, one from each parent, and will be genetically normal (for that particular trait). The risk is the same for each pregnancy.

In a few rare cases, spinal intradural arachnoid cysts may be inherited as an autosomal dominant trait.

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’s syndrome, arachnoiditis, or agenesis of the corpus callosum. (For more information on these disorders, choose the specific disorder name as your search term in the Rare Disease Database.)[2]

Diagnosis is done by MRI, many times the arachnoid cysts are an incidental finding. Myelograms are contraindicated for people with arachnoid cysts. Diagnosis of arachnoid cysts usually only occurs after symptoms are present, and many with the disorder never develop symptoms. Or, in some cases, arachnoid cysts are found incidentally.^[19]

Diagnosis may include a mini-mental state examination (MMSE), a brief questionnaire-based test used to assess cognition.^[11]

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 shunt:^[20]
  • An internal shunt drains into the subdural compartment.^[21]
  • A cystoperitoneal shunt drains to the peritoneal cavity.^{[citation needed]}
• Fenestration:
  • Craniotomy with excision^{[citation needed]}
  • Various endoscopic techniques are proving effective,^[22] including laser-assisted techniques.^[23]
• Drainage by needle aspiration or burr hole. While these procedures are relatively simple, there is a high incidence of recurrence.^{[citation needed]}
• Capsular resection^[12]
• 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.^[24]

Sleep aids are often necessary as most people with Arachnoid Cysts do not sleep.^{[citation needed]}

Untreated, arachnoid cysts may cause permanent severe neurological damage due to the progressive expansion of the cyst(s) or hemorrhage (bleeding).^[2] With treatment most individuals with arachnoid cysts do well with the double edge sword of developing surgical arachnoiditis which can cause its own specific problems and can lead to "popping" another cyst.

More specific prognoses are listed below:

• Patients with arachnoid cysts of the left temporal fossa who experienced impaired preoperative cognition had postoperative improvement.^[25]
• Surgery can resolve psychiatric manifestations in selected cases.^[26]

Arachnoid cysts are seen in 4% of the population.^[27] Only 20% of these have symptoms, usually from secondary hydrocephalus.^[27]

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.^[28]

• Acoustic Neuroma
• Arachnoiditis
• Brain Tumors, General
• Dandy-Walker Syndrome
• Empty Sella Syndrome
• Epidermoids
• Midline Caves of the Brain
• Porencephaly
• Syringomyelia
• Bobble-Head Doll Syndrome
• Hyperprolactinemia
• Panhypopituitarism
• Arnold-Chiari Malformation

Patient support sites:

• arachnoidcyst.org
• arachnoidcyst.net