Glioependymal/ependymal cyst is a rare central nervous system malformation defined as a subarachnoid, supratentorial, interventricular or intraspinal, sometimes intracerebral or intramedullar cyst with an internal ependymal lining, possibly surrounded by glial tissue. It may be an incidental finding or may present at different ages with clinical features depending on its size and location. It may distort adjacent brain structures and cause macrocephaly, ventriculomegaly, hydrocephalus, focal neurological signs and other signs and symptoms. In some cases, it is associated with other cerebral malformations (e.g. corpus callosum agenesis, polymicrogyria, heterotopias). [from
ORPHANET]