Resolution of retro-odontoid cyst in a patient with atlanto-occipital assimilation after occipitocervical fixation

BACKGROUND: Fusion of the atlas with the lower part of the occiput is clinically known as atlanto-occipital assimilation (AOA) or atlas occipitalization. This can be either partial or complete depending on the extent of fusion. AOA is one of the most common congenital anomalies of the craniovertebral junction and is usually asymptomatic. CASE DESCRIPTION: An 80-year-old female presented with a retro-odontoid cyst in conjunction with AOA. Following posterior occipitocervical fixation without resection of the cyst, the patient improved, and the postoperative MR documented cyst resolution. CONCLUSION: Patients with AOA and a retro-odontoid cyst may be successfully managed with occipitocervical fixation without resection of the cyst. However, we would recommend preoperative computed tomography angiography to document whether the vertebral artery follows an anomalous course to avoid an intraoperative neurovascular injury.