This case report describes a patient who presented with myelopathy secondary to a large retro-odontoid post traumatic cicatrix. The objective of this study was to discuss the clinical presentation, pathogenesis, imaging, and surgical management of pseudoarthrosis tissue mass associated with odontoid nonunion. Atlantoaxial subluxation (AAS) has been widely reported in patients with rheumatoid arthritis. AAS leads to repeated cycles of partial tear and repair of ligaments around the altantoaxial complex, resulting in the formation of periodontoid mass (pseudotumor). It is thought that formation of retro-odontoid post traumatic mass (cicatrix), in certain cases of odontoid fracture, is because of similar pathology. This is a retrospective review of case note. Here, the patient underwent posterior decompression through a C1-C2 laminectomy and occipitocervical (C0-C4) fusion with instrumentation, which resulted in dramatic improvement in his symptoms and spontaneous regression of retro-odontoid post traumatic cicatrix. We have described an interesting and a rare case of a large pseudoarthrosis tissue mass associated with odontoid nonunion, which regressed following stand-alone posterior instrumentation. To the best of our knowledge, only a handful of such cases of spontaneous regression of retro-odontoid post traumatic cicatrix following occipitocervical fixation have been described in literature, and our case adds to the growing list of such cases and may help in understanding the natural history of the disease process one day. Although rare, post traumatic cicatrix should be considered as a differential diagnosis of enhancing retro-odontoid mass, especially if there is any history of cervical spine trauma. [ABSTRACT FROM AUTHOR] more...