Diastematomyelia: diagnosis by prenatal sonography.

OBJECTIVE: Diastematomyelia is a form of spinal dysraphia involving a sagittal cleft in the spinal cord with splaying of the posterior spinal elements. This may be an isolated abnormality or in association with more serious dysraphic conditions. In isolated diastematomyelia, the skin is intact and the prognosis excellent. This study aimed to determine the usefulness of prenatal sonography in diagnosing diastematomyelia and in predicting the isolated form. SUBJECTS AND METHODS: The usefulness of the sonographic findings of an extra posterior echogenic focus between the fetal spinal laminae and splaying of the posterior elements for the prenatal sonographic diagnosis of diastematomyelia was assessed in five cases prospectively and in one case retrospectively. The posterior echogenic focus was first seen on prenatal sonograms at a mean age of 19 weeks' gestation (range, 18-20 weeks). The final diagnosis of diastematomyelia was made at autopsy in two cases (one with an associated meningocele), at postmortem radiography in one, at surgery in one, and at CT myelography in two. Postnatal spinal sonograms were obtained in each case. The ability to detect fetal spinal widening on prenatal sonograms was compared with the postnatal radiologic appearance on spinal plain film radiographs.
RESULTS: Diastematomyelia was confirmed in all five cases where the extra posterior echogenic focus was seen at prenatal sonography. The double spinal cord was within a single dural sheath in three cases, with no bony bar present. A double dural sheath with a bony bar was noted in a fourth case. In the fifth case, a bony bar was seen on a postmortem spinal X-ray, but a double dural sheath could not be confirmed because an autopsy was not performed. In the case where diastematomyelia was not suspected on prenatal sonograms, the dural sheath was single and no bony bar was present. Splaying of the posterior elements was seen on postnatal radiographs in all cases but was suspected in only four on prenatal sonograms. Prenatal sonography accurately predicted isolated diastematomyelia in four cases and complicated diastematomyelia in one case. The one case missed prenatally was of isolated diastematomyelia.
CONCLUSION: A diagnosis of diastematomyelia can be made if an extra posterior echogenic focus is seen on prenatal sonography. Splaying of the posterior elements of the fetal spine is frequently present. The pregnancy should be managed differently depending on whether the diastematomyelia is isolated, with the skin intact, or is in association with more serious neural tube defects. This distinction is possible prenatally.