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.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.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
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. Classification
Arachnoid cysts can be found on the brain or on the spine. Intracranial arachnoid cysts usually occur adjacent to the arachnoidal cistern. 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 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 hemorrhage (bleeding).