[Os odontoideum. Presentation in adult age].

The Os odontoideum is a variable oval or round ossicle with a smooth cortical border, which partially corresponds to the odontoid process, without having continuity with the rest of C2 bone. The multifactorial etiology causes instability and clinically translates into pain and compression data into neural structures. The treatment of choice is surgical and techniques have been developed that focus on preserving the stability of the segment. We present the case of a 23-year-old female patient, who begins to suffer at 8 years of age, refers to moderate to severe cervicalgia, which develops with paresthesias in the left hemisphere and later paresis of the left thoracic limb. Physical examination showed hypoaesthesia of the left hemisphere, as well as paresis of the left thoracic limb. Extension studies demonstrate chronic axonal lesion from C1 to C3, predominantly left, imaging studies showing axial instability and magnetic resonance bulbar compression. The patient receives surgical treatment consisting of posterior fixation C1-C2, evolving satisfactorily.