[Retro-odontoid pseudotumor in diffuse idiopathic skeletal hyperostosis].

Retro-odontoid pseudotumors are lesions caused by inflammatory granulation or reactive soft tissue hypertrophy from chronic atlantoaxial subluxation. However, one-third of the cases reported in the medical literature did not show atlantoaxial instability clearly. The authors present the case of a 76-year-old man previously diagnosed with diffuse idiopathic skeletal hyperostosis who presented with severe progressive myelopathy. A magnetic resonance imaging of his cervical spine revealed a retro-odontoid predural mass, which caused a severe compression of the cervical spinal cord. The patient underwent a posterior laminectomy of the atlas and an occipitocervical fusion. After surgery, the pseudotumor was considerably smaller and the neurological symptoms improved.