The odontoid process: a comprehensive review of its anatomy, embryology, and variations

Abstract

A sound understanding of the development of the odontoid process, both in normal and in variant forms, as well as its phenotypical morphology is a prerequisite for the diagnosis and treatment of patients presenting with disorders affecting the cranio-cervical spine.

Basion–Cartilaginous Dens Interval: An Imaging Parameter for Craniovertebral Junction Assessment in Children

“…A secondary ossification center (os terminale) at the apex of the odontoid process appears between 3 and 6 years of age and usually fuses by 12 years. 16,17 The cruciate and alar ligaments share the common mesenchymal origin in the tip of the primitive odontoid process. 12,18 The apical ligament is a functional vestige of the notochord and arises from either the notochord or its sheath.…”

The craniocervical junction: embryology, anatomy, biomechanics and imaging in blunt trauma

“…In relation to the biomechanics of the craniocervical junction and the impact of trauma on this structure, it is useful to visualise the craniocervical junction as composed of two components: the first is a central pillar consisting of the central basiocciput (even though it is anatomically part of the skull base), odontoid process (dens or peg) and the C2 vertebral body; the second component consists of the two-ringed structures surrounding the central pillar—these are the ring of the foramen magnum including the lateral portions of the basiocciput, the exocciput incorporating the occipital condyles and the opisthion (the posterior margin of the foramen magnum), and the ring of the C1 vertebra (atlas) consisting of the anterior and posterior arches and lateral masses of the atlas [2–8] (Fig. 1).…”

“…Once mature, somites differentiate into ventromedial sclerotomes and dorsolateral dermomyotomes. The sclerotomes eventually develop into vertebral bodies, neural arches, ligaments and membranes [2–8]. …”

“…These three segments chondrify at 6 weeks of gestation but remain segregated by the upper and lower dental synchondroses [8–11]. Ossification occurs in three stages: the first ossification centre appears in the body of the the C2 vertebra at 4 months of gestation; the second wave of ossification appears at 6 months of gestation as two ossification centres, one on each side of the basal dental segment—these two centres integrate and fuse at birth when they should have begun to show some attempt at osseous fusion but the non-ossified cartilage may still be evident radiologically into the 6th year of life (Fig.…”

Hypertrophy of the transverse ligament caused by os odontoideum: a case report

“…[2][3][4] Odontoid process of the axis has many variations that may either be congenital or acquired and lead to mild or severe instability of the atlanto-axial joint leading to potential defects on the medulla or upper cervical cord with neurological symptoms. [5] The identified congenital anomalies of the odontoid process are aplasia, hypoplasia, duplication, condylus tertius, ossiculum terminale (os avis), and OO. [6,7] OO is the most common anomaly of the odontoid process.…”