Osteoid osteoma of the odontoid process of the axis associated with atlanto-axial fusion.

Osteoid osteoma is a primary benign bone tumour with characteristic imaging and pathological features. In about 10% of the cases it involves the spine, especially the posterior elements. We report a pathologically proven case of osteoid osteoma of the odontoid process of the second cervical vertebra associated with atlanto-axial fusion. The case was diagnosed pre-operatively using plain radiography, multiplanar helical CT, contrast-enhanced MRI and radioisotope bone scanning.