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. Seizures
Hydrocephalus (excessive accumulation of cerebrospinal fluid)
Increased intracranial pressure
Developmental delay
Behavioral changes
Nausea
Dysdiadokinesis
Hemiparesis (weakness or paralysis on one side of the body)
Ataxia (lack of muscle control)
Musical hallucination
Pre-senile dementia, a condition often associated with Alzheimers disease
In elderly patients (>80 years old) symptoms were similar to chronic subdural hematoma or normal pressure hydrocephalus:Dementia
Urinary incontinence
Hemiparesis
Headache
Seizures

Location-specific symptoms
A supratentorial arachnoid cyst can mimic a Ménières disease attack. Frontal arachnoid cysts have been associated with depression. Cysts on the left temporal lobe have been associated with psychosis. A left fronto-temporal cyst showed symptoms of alexithymia. Cyst on the right sylvian fissure resulted in new onset of schizophrenia-like symptoms at age 61. A patient with a cyst on the left middle cranial fossa had auditory hallucinations, migraine-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.
However, with treatment most individuals with symptomatic arachnoid cysts do well.More specific prognoses are listed below:

Patients with impaired preoperative cognition 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 population with a gender distribution of 2:1 male:female. Only 20% of these have symptoms, usually from secondary hydrocephalus.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. See also
References


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