Congenital Malrotation of the Atlas with Unilateral Hypertrophy of the Atlanto-occipital Joint-A Rare Anomaly of the Craniovertebral Junction and Its Management

BACKGROUND: Congenital anomalies are commonly encountered in the craniovertebral junction because of its unique embryologic development. The craniovertebral junction usually comprises the occiput, atlas, and axis. However, malrotation of the atlas (C1) in between the occiput (C0) and axis (C2) with Chiari I malformation as well as unilateral hypertrophy of the atlanto-occipital joint and a lateral mass manifesting features of high cervical myelopathy is a rarely reported anomaly. CASE DESCRIPTION: A 22-year-old woman presented to us with high cervical compressive myelopathy. Imaging revealed rotation of the C1 vertebra approximately 20 degrees toward the left side with right atlanto-occipital joint dislocation and hypertrophy. Imaging also revealed hypertrophy of a right lateral mass of C1, Chiari I malformation, and right atlantoaxial dislocation exposing the right C2 superior facet. She underwent a right extreme far lateral approach comprising a right C1 posterior arch excision and medialization of the right vertebral artery with excision of the hypertrophied atlanto-occipital joint extradurally and posteromedial excision of the superior articular facet of C1. The patient's compressive myelopathy features improved postoperatively. CONCLUSIONS: We report the successful management of this rare congenital anomaly and review the literature.