[citation needed] 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 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.

[20] A recent study shows differences in communication between the arachnoid cyst and the subarachnoid space by CT cisternography.

[21] A comparison of arachnoid cyst fluid and CSF in a series of patients show differences in chemical composition.

[23] Spinal arachnoid cysts may be extradural, intradural, or perineural and tend to present with signs and symptoms indicative of a radiculopathy.

[23] Arachnoid cysts may also be classified as primary (congenital) or secondary (acquired) and have been reported in humans, cats, and dogs.

[citation needed] More specific prognoses are listed below: Arachnoid cysts are seen in up to 1.1% of the population[34][35] with a gender distribution of 2:1 male:female.