Retro-odontoid pseudotumor presenting double layer on MRI: A case report

BACKGROUND: Retro-odontoid pseudotumors (ROPs) typically present as a single mass posterior to the odontoid ranging from isointense to hypointense relative on T1-weighted magnetic resonance (MR) imaging (MRI T1WI). Here, a patient with ROP exhibited the double-layer sign on the MRI T1WI characterized by an initial ventral layer posterior to the odontoid process followed by a secondary dorsal layer. CASE DESCRIPTION: An 84-year-old male presented with cervical myelopathy attributed to ROP resulting in atlantoaxial instability on dynamic X-ray studies, and the double-layer sign on the T1 MR accompanied by a cystic component. MR following C1–C2 posterior fusion, the patient’s myelopathy resolved and both layers spontaneously regressed on the follow-up MR studies. CONCLUSION: The MR-documented double layer sign with ROP, likely attributable to reactive hypertrophy of the transverse ligament with cystic components, may demonstrate spontaneous MR regression with symptom resolution following a C1–C2 posterior fusion.