Unilateral axis facet hypertrophy--a rare case of irreducible rotatory atlantoaxial dislocation and a review of the literature.

Fixed atlantoaxial dislocations are difficult to treat and there is no consensus in the treatment protocol. Unilateral enlargement of the atlas-axis facet complex in fixed atlantoaxial dislocations is a very rare condition. These pathologies are usually quite unstable and surgical treatment is necessary in unreductable cases. A 52-year-old woman with a diagnosis of irreducible-fixed rotatory atlantoaxial dislocation presented with acute onset of dizziness, loss of balance, and tetraparesis. She was under 8 years of conservative follow-up. Review of radiology revealed unilateral C2 superior facet hypertrophy compressing the medulla and obstructing the vertebral artery. To treat this condition, we have used a posterior midline approach and removed the lateral portions of the posterior rim of the foramen magnum and the assimilated posterior arch of C1. The V3 segments of the vertebral arteries were exposed bilaterally. The atlantoaxial joint complex on the left was hypertrophied compressing V3. We have removed hypertrophied lateral mass of the atlas and the hypertrophic superior articular facet of C2 for decompression. Patency of both vertebral arteries were checked intraoperatively by Doppler and indocyanine green angiography. We have fixated craniocervical junction on the same session. Patient was neurologically intact and she had confirmed fusion on the surgical site after three years of follow-up. This is a rare case of unilateral hypertrophy of the C2 superior articular facet in a fixed atlantoaxial rotatory dislocation. Progressive compression of medulla and the left vertebral artery leaded to clinical worsening of neurology in this case after 8 years of follow-up. Surgical treatment was necessary for neurological decompression and to establish stability.