Cervical Myelopathy due to Idiopathic Retro-odontoid Pseudotumor.

A retro-odontoid pseudotumor (ROP) is commonly associated with atlantoaxial instability or rheumatoid arthritis. However, ROP in the absence of atlantoaxial instability or rheumatoid arthritis, which is termed idiopathic ROP (IROP), is a rare condition. The pathomechanisms and optimal treatment strategies for IROP remain controversial. The aim of the present study was to evaluate the radiographical and clinical characteristics of IROP patients and to assess the efficiency of atlantoaxial/occipitocervical fusion on IROP regression.Data from five patients diagnosed with IROP were retrospectively reviewed. Posterior atlantoaxial or occipitocervical fixation and fusion was performed in four patients and C1 posterior arch resection alone in one patient. The patients' features, surgical procedures, and complications were recorded. The retro-odontoid soft tissue thickness was measured on preoperative and postoperative magnetic resonance imaging to evaluate IROP regression.The mean follow-up time was 37 months. ROP regression was achieved in patients who received atlantoaxial/occipitocervical fusion, but not for the patient with C1 posterior resection alone. There were no observed neurovascular complications associated with surgery.IROP was related to a restricted range of motion of the subaxial spine. Upper cervical fixation is an optional treatment that produces IROP regression over time. By contrast, direct removal of the IROP is unnecessary.