Clinical indications for computer-assisted myelography

Computer-assisted myelography (CAM) is a technique in which computed tomography (CT) is combined with the intrathecal administration of metrizamide to demonstrate the spinal cord and surrounding structures. This retrospective study of 139 CAMs performed at Emory University Hospital included 125 CAMs that were preceded by routine metrizamide myelography (secondary CAM). The remaining 14 CAMs were primary studies without concomitant myelography. These CAMs and conventional myelograms were reviewed to provide indications for the use of CAM as a replacement for other radiodiagnostic studies or as an adjunct to radiological diagnosis. Eighty-one CAMs (58%) were positive for some pathological process. Of the 69 secondary CAMs demonstrating a pathological condition, 46 (67%) revealed some aspect of the lesion not apparent on routine metrizamide myelography. In no case with positive myelography was CAM negative. However, conventional myelography often added valuable diagnostic information. Although high resolution CT has allowed limited visualization of the spinal cord, CAM is often indicated for cases in which diagnosis requires more definition of cervicomedullary, extradural, intradural, extramedullary, and intramedullary lesions. Our clinical review found CAM to be extremely useful in the diagnostic evaluation of pathological conditions involving the spine and spinal cord and suggests clinical indications for the use of CAM based upon selected illustrative cases. Furthermore, CAM seemed to be superior to other radiological procedures in certain instances, such as in cases of spinal dysraphism and in the evaluation of lesions at the foramen magnum. Until more experience is obtained using spinal CT and CAM, CAM should not replace myelography altogether. The present study indicates that, rather than replacing conventional CT and myelography, CAM should be used as a primary study in situations where it has been shown to be superior and as a complementary study when other neurodiagnostic examinations are equivocal or nondiagnostic.