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A case of spinal cord compression from an intradural arachnoid cyst in the thoracic region is reported. The patient was a 59-year-old female. She had noted thoracic girdle pain and urinary trouble for 2 years. Neurologically, she showed muscle atrophy and weakness of the right leg, and loss of all sensory modalities below the 7th thoracic cord (Th7) level bilaterally. Metrizamide myelography showed no abnormal findings, but computed tomography (CT) following the metrizamide myelography demonstrated marked enlargement of the subarachnoid space and remarkable rightward and ventral displacement of the spinal cord. During surgery it was noted that the spinal cord was severely compressed by an arachnoid cyst from Th4 through Th6. After this operation, neurological deficits disappeared completely.
Most spinal intradural arachnoid cysts arise in the region of the septum posticum in the thoracic portion. Various etiologies have been postulated. Although conventional myelogram has been the most important form of examination, intradural arachnoid cysts may be filled incompletely or not at all in the myelography performed in a prone position, because they mostly locate on the dorsal aspect of the spinal cord. There are some reported cases in which intradural arachnoid cysts were found a few hours after myelography. Therefore it is not so easy to diagnose intradural arachnoid cysts with conventional myelography. With metrizamide CT myelography, intradural arachnoid cysts can be visualized more easily.
