Occurrence of the anterior tubercle in the margin of the occipital foramen

The occipital foramen is an extremely important region, due to the passage of several neurovascular structures, such as accessory nerves, spinal, bulb (or medulla oblongata), and vertebral arteries.1,2 However, the presence of a tubercle in the margin of this foramen, may cause locks and compression of these structures,2 osteoarthritis of the atlanto-axial joint leading to basilar invagination and periodontal ligament degeneration3,4 as well as craniocervical instability.1 The occurrence of the anterior tubercle in the margin of the occipital foramen varies from 1.3% to 15%;5–8 and has been attributed to the ossification of the apical ligament of the odontoid process of the axis.9,10 The aim of this study was to determine the incidence of tuber at the occipital foramen margin.