Sagittal Diameter of the Cervical Spinal Canal in Children

Abstract

The concept of using radiographic measurements in the diagnosis of intraspinal lesions is not new. Recognizing that tumors can enlarge the spinal canal by erosion, Elsberg and Dyke determined the range of maximum normal adult values for the interpediculate distances of vertebral bodies as defined on the anteroposterior radiograph of the spine and demonstrated that even small localized increases of these measurements were of diagnostic significance (3). The interpediculate distance is of little value in studying the cervical spine. The pedicles are often not demonstrable above C-5. Furthermore, the “pedicle” shadows of cervical vertebrae, unlike their thoracolumbar counterparts, represent the bases of the laminae rather than the pedicles themselves. Cervical pedicles, being oblique to the sagittal plane, project no oval shadow on the anteroposterior film. The medial margins of the so-called pedicle shadows represent the greatest diameter of the cervical neural canal, the one which consequently may be the last to be altered in the presence of an expanding intraspinal lesion. The past decade has witnessed an increasing interest in cervical spine roentgenograms. Partly as a result of the deficiencies of cervical interpediculate measurements, there has developed an awareness of the diagnostic significance of the sagittal diameter of the cervical spinal canal (Fig. 1). Importance has been ascribed to both the decreased sagittal measurements in cervical spondylosis (6, 14) and the increased measurements associated with intraspinal tumors (1, 13,). The present investigation concerns only children. Interest is focused on the value of the sagittal measurement for diagnosis of intraspinal tumor and on the potential value of this measurement in the study of developmental narrowing of the spinal canal. Tumors There seem to be no data available permitting reasonable estimation of the incidence of abnormal sagittal diameters in children with tumor. Since, however, it is the smallest diameter of the cervical spinal canal, it should be a relatively sensitive gauge of early radiographic change, particularly with intramedullary tumor. Boijsen showed that of 7 patients with spinal tumor with skeletal changes, 5 had an increased sagittal diameter, while only 2 showed distinctly pathological interpediculate distances. In none were there increased interpediculate measurements without concomitant enlargement of the sagittal diameter. Enlargement of the canal may result from tumor erosion of bone or, in the case of tumors of childhood, the growth of the vertebrae may be so modified that they accommodate the expanding intraspinal mass without showing evidence of erosion (13) (Fig. 6). Those who have critically observed the behavior of the vertebral column in the presence of tumor seem to agree that the growing spine is more susceptible to the influence of an expanding mass than the adult spine.