Cervical myelopathy involving os odontoideum with retro-odontoid cyst and atlanto-axial instability: A case report

Os odontoideum is an unusual anatomic variant of the dens of C2 defined as an independent ossicle separated from the axis; the etiology is a topic of debate, with investigative studies supporting congenital and traumatic origins, clinical manifestations vary from asymptomatic forms, underlying C1-C2 instability to compression of the spinal cord or vertebrobasilar ischemia. We report a case of a patient with a history of minor trauma 5 years ago, she suffered from neck pain. The clinical examination was normal. Radiological examination including X-ray, CT, and MRI showed cervical myelopathy involving os odontoideum with C1-C2 instability and compressive retro-odontoid cyst. Imaging has an important role in the management of os odontoideum, from diagnosis to therapy.