Spinal cord size in syringomyelia: change with position on metrizamide myelography.

Change in the anteroposterior diameter of the cervical spinal cord was demonstrated on metrizamide myelography in 20 out of 40 cases of cervical syringomyelia. Twelve of these were normal-sized cords, four were small, and four enlarged. Comparable lateral cervical myelograms in the prone and supine positions were sufficient to show size change for normal-sized or small cords. Additional myelograms in the erect and Trendelenburg positions were necessary to show size change in enlarged cervical cords, especially with associated Chiari malformation. A localized change in cord size suggests syringomyelia. If the change in cord size is diffuse, then change less than 10% is not necessarily significant. In undiagnosed myelopathy, metrizamide myelography has the potential to detect unsuspected syringomyelia even when the cord is normal-sized or small. Myelographic study may also be useful as an adjunct to delayed computed tomographic studies.