Os odontoideum syndrome: pathogenesis, clinical patterns and indication for surgical strategies in childhood.

Os odontoideum is a rare condition with a controversial pathogenesis and poorly understood natural history. Hypoplasia of the odontoid associated with an independent oval ossicle, with smooth margins widely separated from C2 and well above the superior facets of the axis, is termed "os odontoideum". The neurological manifestations arise from bulbospinal compression both at rest and during motion, due to the craniovertebral junction (CVJ) instability itself. Consequently, the surgical management of os odontoideum should aim at achieving both neural decompression and stabilization of the CVJ. The aims of this paper are to introduce the embryological steps involved in the CVJ development, to underline the updated theories propounded to interpret developmental and congenital disorders of the os odontoideum, to introduce the most updated surgical techniques and to discuss some exemplary cases selected from our personal experience.