Differential Diagnosis of Intradural (Extramedullary) and Extradural Spinal Canal Tumors

Intraspinal tumors are usually readily detected by myelography. However, although the level of the lesion within the spinal canal is accurately determined by this means, a more precise localization is desirable. In order to accomplish this objective, reliable criteria must be established to permit separation of extradural and intradural lesions. The myelographic findings in combination with the changes seen on the plain spine roentgenograms, together with the clinical observations, might then permit prediction of the histologic diagnosis with reasonable accuracy. This paper is a review of the intraspinal tumors (exclusive of intramedullary lesions) observed at the Montefiore Hospital (New York) in recent years and confirmed by surgery or postmortem examination. In this analysis special attention will be given to the plain-film and myelographic findings noted in the two groups of spinal canal tumors, and criteria for their diagnosis will be presented. Myelographic Technic For precise diagnosis, opaque myelography should be combined with fluoroscopy and fluoroscopic spot-filming. Although the level of a mass may be determined by gas myelography, the findings are less accurate than with an opaque medium, which affords a more precise definition of the abnormality. Epidural introduction of gas or an opaque medium for myelography has not been widely used and is limited to the diagnosis of extradural lesions. In standard subarachnoid myelography an adequate volume of opaque medium is required. In the lumbar region 9 c.c. are recommended, and 9 to 12 c.c, are generally used in the thoracic and cervical segments. The lumbar route is preferable, but cisternal injections may at times be necessary, alone or in conjunction with lumbar injection. A combined lumbar and cisternal procedure may be done when it is desirable to outline the upper and lower limits of an extensive tumor or in a search for additional abnormalities when there is a complete block with lumbar myelography. Fluoroscopic observations are made following the introduction of the opaque material into the subarachnoid space. With proper injection there will be a free flow of the medium in contrast to what is seen with subdural or extradural injection. Frontal, oblique, and translateral views are obtained. Frequently, the lateral decubitus position may be useful. Inasmuch as the injecting needle is usually left in place during the examination, most patients are studied in the prone position. An opaque medium heavier than spinal fluid will, however, settle to the ventral aspect of the subarachnoid space, with inadequate opacification of the more dorsal aspect. Thus, in some instances, it is desirable to study the patient in the supine position as well. Roentgenographic exposures should, of course, be of adequate penetration to permit visualization of the cord, nerve roots, and any mass within the subarachnoid fluid.