[Measurement of the normal cervical spinal cord in metrizamide CT myelography]

The shape of the spinal cord is the most important factor in diagnosis of spinal disorders by metrizamide CT myelography (met. CT). Even in cases where the spinal cord looks normal in shape its size might be abnormal, for example in cases with spinal cord atrophy, syringomyelia, intramedullary tumor and several other conditions. In detecting the slightest abnormality in such cases, it is absolutely necessary to have in hand the knowledge of the normal size of the spinal cord at each level. We measured, therefore, the sagittal and transverse diameters of the cervical spinal cord in 55 patients with no known lesions on met. CT. Comparing our results with those by others, we found some differences as to the size of the spinal cord. We assume that these differences are due to the differences in resolution of the CT scanners used. The size of the spinal cord tends to measure larger with a CT scanner with high resolution than with others. Previous authors reported that the size of the spinal cord would vary by window center settings. Our experimental results indicate, however, that window center settings do not significantly affect the measurements. It is concluded that the normal values of the spinal cord dimensions at each level somewhat differ by CT equipments used. One should have normal values with one's own equipment in hand in order to take full advantage of this sophisticated diagnostic technique.