Case of spontaneous regression of DISH-associated retro-odontoid pannus following occipto-cervical fusion

Background: Retro-odontoid pannus is a reactive fibrocartilaginous mass that develops posterior to the odontoid process, causing ventral compression of the cervicomedullary junction. Although classically associated with rheumatoid arthritis, it is increasingly recognized in non-inflammatory conditions (e.g., diffuse idiopathic skeletal hyperostosis [DISH]) driven by chronic atlantoaxial instability. Over the past two decades, posterior stabilization alone has emerged as the preferred first-line approach, inducing spontaneous pannus regression by eliminating pathological motion. Case Description: An 85-year-old male with DISH and extensive subaxial cervical ankylosis presented with severe occipital/cervical pain. The magnetic resonance imaging (MRI) revealed a retro-odontoid soft-tissue mass that peripherally enhanced with gadolinium, resulting in cervicomedullary compression. Following an occipitocervical decompression/fusion (C0–C2), MRI 6 months later demonstrated spontaneous regression of the retro-odontoid mass. Conclusion: Posterior occipitocervical stabilization readily addresses degenerative retro-odontoid pannus formation attributed to DISH and may resorb following C0-C2 fusion.