Concerning the Diagnosis of Lesions in the Lower Spinal Canal

PAIN in the lower back, radiating into one or both legs is a common ailment; one for which many remedies have been proposed and probably as many theories of its etiology offered. Until comparatively recent years, most investigators' attention has been focused upon extraspinal causes: the sacro-iliac joints, postural deformities, fascial bands, taut pyriformis muscles, the vertebral articular facets, and ill-defined toxic, allergic, or infectious involvements of peripheral nerves. Intraspinal lesions, if considered at all, were listed near the end of the differential diagnosis. The steadily increasing number of reported cases of low intraspinal lesions causing low back pain, particularly herniated nuclei pulposa (1, 2, 3, 4, 5, 6, and many others), and hypertrophied ligamenta flava (7, 8, 9, 10, 11), prompts the suggestion that these lesions are far more common than generally supposed. Accurate localization of tumors in the lower lumbar neural canal from clinical findings alone has been and probably will continue to be, a difficult problem, due to anatomical peculiarities of the region. In the first place, lesions of the cauda equina may produce symptoms identical to lesions of the corresponding peripheral nerves. Unless the lesion involves one nerve root alone and, therefore, gives pain, with or without sensory loss, corresponding to the segmental skin distribution of that root, it may be most difficult to localize its exact site. In the second place, many intraspinal lesions are sufficiently large to produce intractable pain, yet they yield negative findings on careful neurological examinations, such as normal sensory test, normal motor function, and normal reflex activity (see Fig. 5). This may be explained when one considers the large size of the neural canal in the lumbar region and the freely movable roots of the cauda equina. It is only as the roots leave the intervertebral foramina that they become relatively fixed. Therefore, a large lesion in this region may shift freely the caudal roots, except at their fixation points without producing destructive symptoms and signs. Much of our progress to date in unraveling the mysteries of the lower spinal canal has been made possible by accurate roentgenological studies after injection into the subarachnoid space of some contrast medium for visualization. As our understanding increases, we may be able to relegate the laboratory tests to a place of secondary importance to the clinical study but that stage of development has not yet been reached. Lipiodol and air have been used successfully for visualization of the neural canal. We freely admit that of the two, air is preferable insofar as local irritative effects are concerned, but when considered from the standpoint of accurate diagnosis of other than gross lesions, lipiodol is much superior. Lipiodol causes a local reaction in the meninges, the degree of which is largely dependent upon the presence of free iodine in the compound.