The exact cause of<unk> s is not known. Researchers believe that most cases of<unk> s are developmental malformations that arise from the unexplained splitting or tearing of the<unk>  membrane. In some cases,<unk> s 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<unk> s is unknown. There are some cases where hereditary disorders have been connected with<unk> s. Some complications of<unk> s 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<unk> s are a true congenite condition or if this should be separated from secondary cysts. A recent study shows differences in communication between the<unk>  and the subarachnoid space by CT cisternography. A comparison of<unk>  fluid and CSF in a series of patients show differences in chemical composition.<unk> s can also occur secondary to other disorders such as Marfan syndrome,<unk> itis, or agenesis of the corpus callosum.
Arachnoid cyst
Subdural hygroma
Labyrinthine fistula
Frontal horn cyst
Cystic hygroma
Choroid plexus papilloma
Choroidal fissure cyst
Hemicrania continua