Diastematomyelia

Diastematomyelia is a congenital malformation of the neural axis characterized by a sagittal division of a segment of the spinal cord or cauda equina and usually associated with anomalous development of the vertebrae. The two lateral portions of the cord are separated by an osseous or fibrocartilaginous septum which is attached anteriorly to one or more vertebral bodies, posteriorly to the dura, and occasionally to the deformed vertebral arches as well. Herren and Edwards (3) were able to collect from the literature 42 cases which they considered examples of true diplomyelia and added another. Since then we have found 9 additional reported cases (1, 2, 5–9). In 1946, Maxwell and Bucy (8) stated that only 4 of the recorded cases were diagnosed before autopsy; these were recognized at operation. No reports have been found of cases in which the diagnosis was made preoperatively. We believe that the diagnosis can be made in most cases by roentgenograms of the spine because of the associated bony abnormalities. It is the purpose of this paper to present the roentgen criteria for such a diagnosis. Roentgenograms of the spine will be fully described later. In essence, they show a fusiform widening of the interpedicular spaces over several spinal segments. Most of our cases also show an osseous spur in the approximate center of the widened spinal canal, best seen in the anteroposterior projection. Myelograms have been obtained preoperatively in 7 patients and all have shown a filling defect of the pantopaque column at the midline bony spicule. At operation, this bony spur proved to separate the two portions of the spinal cord and to be attached to the posterior surface of the vertebral body. Twelve cases of transfixation of the neural axis have now been proved by operation at The Children's Hospital of Boston. In 10 the diagnosis was made preoperatively. Six other patients suspected, on the basis of the roentgen findings, of having diastematomyelia are awaiting operation. Nine of the proved lesions occurred in the cord and 3 in the cauda equina. They are grouped together because embryologically, clinically, and roentgenologically they appear similar. The osseous or fibrocartilaginous septum passing through the cord or cauda equina fixes the cord in a low anatomical position, so that its normal ascent during growth of the bony spine is impaired. This septum, and the arachnoid adhesions which frequently accompany it, produce traction on the cord or cauda equina that results in neurologic disturbance and in many reported cases has led to the Arnold-Chiari malformation and hydrocephalus, although in our series only one patient exhibited hydrocephalus secondary to an Arnold-Chiari deformity. Diastematomyelia is most frequently observed in the lumbar region. We have, however, seen it as high as the level of the seventh thoracic vertebra.