Metrizamide is largely replacing iophendylate (Pantopaque) for routine lumbar myelography. Better visualization of the nerve root sheaths should make metrizamide myelography more sensitive in detecting laterally herniated disks, such that epidural venography might be required less often. However, that expectation has not been realized. In over 800 consecutive myelograms, one-half obtained with iophendylate and one-half obtained with metrizamide, 60 patients still required epidural venography. Nearly as many had metrizamide as had iophendylate (28 versus 32). Further, the number of positive epidural venograms with herniated disks confirmed at surgery was not significantly different (12 versus 11). Epidural venography is still indicated after negative or equivocal metrizamide myelography if strong clinical suspicion of herniated disk persists.
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