Imaging of thoracic and lumbar spinal extradural arachnoid cysts: report of two cases.

Extradural arachnoid cysts are uncommon expanding lesions in the spinal canal which may communicate with the subarachnoid space. Usually in the lower thoracic spine, they may cause symptoms by compressing the spinal cord or nerve roots. We report cases of thoracic and lumbar arachnoid cysts studied by cystography, myelography, CT and MRI. These techniques showed extradural cystic lesions containing cerebrospinal fluid, with variable communication with the subarachnoid space, causing anterior displacement and flattening of the spinal cord.