Anteroposterior Spondyloschisis of Atlas With Incurving of the Posterior Arch Causing Compressive Myelopathy

Study Design. A case report of a patient with a combined anterior and posterior arch anomaly of atlas leading to compressive myelopathy. Objective. To describe a rare presentation of cervical stenosis at the atlas where congenital defects of the posterior arch with an incurving portion exists. This report includes a feasible hypothesis for the development of this anomaly on the basis of previous hypotheses and surgical findings. Summary of Background Data. Congenital defects of the posterior arch of atlas are uncommon and congenital symptomatic cervical stenosis is very rarely seen at this level. The congenital midline cleft of the posterior arch of an atlas has been described in patients with progressive motor symptoms and sensory deficit in extremities. Methods. An 11-year-old boy suffered from right side weakness for 1 year. His mother witnessed his awkward walking and clumsiness in using chopsticks and writing. His medical history was unremarkable, and there was no history of significant trauma. Right upper limb weakness of Grade IV/V and difficulty in hopping on right leg was checked on neurologic examination. The magnetic resonance image showed cervical canal stenosis at atlas level and high signal intensity change in the spinal cord. The computed tomography demonstrated partial defect at anterior and posterior arch of the atlas with incurving at defect site leading to cord compression. Suspecting one of craniovertebral junction anomalies, we performed a surgical resection of the posterior arch of the atlas (decompressive laminectomy). Results. The laminectomy was done. The defect site of the posterior arch was substituted with a cartilage and there was no dural adhesion. After surgery, right lower limb weakness was improved and no instability has been observed during 1-year follow-up. Conclusion. We describe the association between compressive myelopathy and combined anteroposterior spondyloschisis of an atlas with incurving of the arch at defect site. Both computed tomography and magnetic resonance image were required to demonstrate the bony configuration and cord compression. And decompressive laminectomy of atlas was effective as a treatment for this compressive myelopathy caused by midline defect in the posterior atlantal arch with bony incurving.