Intramedullary penetrance of metrizamide in the dog spinal cord.

Metrizamide computed tomography (CT) myelography is clinically useful in the detection of syringohydromyelia. The mechanism by which intrathecally injected metrizamide migrates into the intramedullary cavity is unknown, although reflux into the central canal of the cord via the obex has been postulated. Since intrathecally injected metrizamide has been shown to penetrate normal brain, similar penetrance of the spinal cord might be expected. Five anesthetized mongrel dogs were examined with sequential CT scanning of the cervical spine for 24 hr after intrathecal introduction of metrizamide. The attenuation values of the specified subarachnoid space and the spinal cord at the level of the atlantoaxial joint were recorded. A significant and reproducible increase with time in attenuation values within the cervical spinal cord accompanied by a progressive decrease in attenuation values of the subarachnoid space was observed. The proposed mechanism of cord enhancement, the implication for cord imaging, and the analysis of patients with syringohydromyelia are discussed.