Hypoplasia of C1's posterior arch: Is there an ideal anatomical classification?

Background: Congenital anomalies of the atlas are rare and usually occur in conjunction with other congenital variants. They include a wide spectrum of anomalies ranging from clefts to hypoplasia or aplasia of its arches that may contribute to spinal cord compressive syndrome.

Case Description: A 54-year-old male presented with the sudden onset of a severe quadriparesis and loss of proprioception after a minor fall. The magnetic resonance (MR) scan showed cord compression at the C1 level attributed to C1 arch hypoplasia. Two months following a decompressive C1 laminectomy without fusion, and the patient was symptom free.

Conclusion: Posterior C1 arch hypoplasia is a rare anomaly that can contribute to cervical cord compression and myelopathy. The optimal surgical management may include, as in this case, a posterior decompression without fusion.