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[Extradural arachnoid cyst of the dorsal region with relapsing and recurrent development].

An extradural arachnoid cyst of the thoracic spine was diagnosed and operated in a 39 year-old woman with a history of two regressive attacks of spastic paraplegia during a 19 year-period. The diagnosis was established by magnetic resonance imaging and myeloscan, which demonstrated the cyst and its consequences on the spinal cord and the spine. Theories of etiology and development of extradural arachnoid spinal cysts are reviewed.