Retro-odontoid pseudotumor without atlantoaxial subluxation.

A retro-odontoid pseudotumor (ROP) is commonly associated with atlantoaxial subluxation (AAS). Here, we report a patient with ROP but without AAS. The patient was a 72-year-old man who did not have a history of rheumatoid arthritis or trauma to the head and neck. The patient was admitted to our hospital with gait disturbance, progressive motor weakness in both upper extremities and sensory disturbance in all four extremities. MRI showed a retro-odontoid mass with severe compression of the cervical spinal cord. A CT scan showed spondylotic changes in C5, C6, and C7 and bilateral facet fusion between C3 and C4. Dynamic radiography showed no evidence of AAS; there was loss of mobility at C2-C7 and excessive mobility at C1. Intraoperative pathological examination revealed that the lesion was a pseudotumor; therefore, posterior C1-C2 fixation was performed. MRI performed 6 months after the operation revealed that the pseudotumor was markedly reduced. To the best of our knowledge, patients with ROP without AAS are uncommon.