A rare, mostly benign, primary tumor of the meninges (arachnoid cap cells), usually located in the supratentorial compartment, commonly appearing in the sixth and seventh decade of life, clinically silent in most cases or causing hyperostosis close to the tumor and resulting in focal bulging and localized pain in less than 10% of cases. Additional features may include headache, seizures, gradual personality changes (apathy and dementia), anosmia, impaired vision, exophthalmos, hearing loss, ataxia, dysmetria, hypotonia, nystagmus, and rarely spontaneous bleeding.

Paralysis of voluntary muscles means loss of contraction due to interruption of one or more motor pathways from the brain to the muscle fibers. Although the word paralysis is often used interchangeably to mean either complete or partial loss of muscle strength, it is preferable to use paralysis or plegia for complete or severe loss of muscle strength, and paresis for partial or slight loss. Motor paralysis results from deficits of the upper motor neurons (corticospinal, corticobulbar, or subcorticospinal). Motor paralysis is often accompanied by an impairment in the facility of movement.