MR imaging of thoracic extradural arachnoid cysts

: Two extradural arachnoid cysts of the thoracic spine were studied with magnetic resonance imaging, myelography, and CT. Magnetic resonance imaging correctly characterized the extradural location of the cysts as well as the cyst contents as CSF, thus establishing the diagnosis. Magnetic resonance is helpful in the assessment of the extent of cord atrophy and myelomalacia and may be of predictive value in the postoperative prognosis.