Atlanto-occipital Assimilation with Basilar Invagination and Atlanto-occipital Dislocation Treated by Occipitocervical Fixation: A Rare Case Report.

Introduction: Atlanto-occipital assimilation is the most common osseous anomaly of the cervical-occipital junction. The incidence rate of occipitalization has been reported 1.42.5/1000 children. Most of the patients are asymptomatic initially. Clinical features usually appear after 3rd decade depending on the level and degree of spinal cord compression with surrounding vital structures such as vertebral artery involvement. Hence, early definitive diagnosis and subsequent successful treatment are necessary in such cases to prevent life-threatening complications.

Case Report: A 16-year-old male presented with neck pain and progressive weakness of the bilateral lower limb since the past 2 months suffering from difficulty in walking, giddiness, and numbness of his fingertips. Hoffman's sign was positive. Plain cervical spine radiography (AP and lateral) is falsely suggestive of the absence of an atlas. MRI revealed the tip of the dens projecting 1314 mm above the Chamberlains line suggestive of basilar invagination. Occipito-cervical fixation was planned with an occipital plate, laminar, pedicle screw, and rods. Occipital plate fixed with screws (6,8 mm). C2 vertebra fixation with pedicle screw and laminar screws and C3 vertebra with a lateral mass screw under C-arm guidance. The patient mobilized with a walker from post-operative day 2 and then he ambulated unaided.

Conclusion: Different types of atlanto-occipital assimilation have been reported. Treatment modality completely depends on neurological symptoms and instability.Although, different surgical options are available, occipito-cervical fixation with occipital plate, screws, and rod fixation is the most superior surgical technique for atlanto-occipital assimilation with atlanto-occipital instability.