Search

The embryonic occipital bone and odontoid process of the axis are attached and connected by the notochord, but become separated in later development and growth. With special attention to the process of separation, we examined sagittal sections of the craniocervical junction in 18 human fetuses at 8-16 weeks and 22 fetuses at 31-37 weeks. At 8-9 weeks, the anterior arch of atlas was always seen overriding the occipital basal part. The odontoid process was close to the occipital with or without a transient joint cavity until 16 weeks. Near term, the top of the odontoid process was usually higher than the anterior arch, but the former was sometimes (7 of 22) at a level almost equal to or lower than the latter. The apical ligament was evident in a few specimens (5 of 22). A distance between the occipital basion and odontoid process was sometimes less than 1.5 mm (8 of 22) or less than half the thickness of the arch (10 of 22). A transient joint cavity between the basion and odontoid process was often (10 of 22). In three fetuses near term, the atlanto-occipital joint cavity was continuous with the median atlanto-axial joint cavity, and the anterior arch was overriding the occipital basal part. Therefore, rather than stage or age, individual differences were evident in the topographical relationship between the three bony elements at the craniocervical junction. An understanding of the embryology and normal development will aid in the correct interpretation of radiologic images of the pediatric cervical spine., (© 2020 American Association for Anatomy.)

Purposes: The detailed understanding of the anatomy and timing of ossification centers is indispensable in both determining the fetal stage and maturity and for detecting congenital disorders. This study was performed to quantitatively examine the odontoid and body ossification centers in the axis with respect to their linear, planar and volumetric parameters., Methods: Using the methods of CT, digital image analysis and statistics, the size of the odontoid and body ossification centers in the axis in 55 spontaneously aborted human fetuses aged 17-30 weeks was studied., Results: With no sex difference, the best fit growth dynamics for odontoid and body ossification centers of the axis were, respectively, as follows: for transverse diameter y = -10.752 + 4.276 × ln(age) ± 0.335 and y = -10.578 + 4.265 × ln(age) ± 0.338, for sagittal diameter y = -4.329 + 2.010 × ln(age) ± 0.182 and y = -3.934 + 1.930 × ln(age) ± 0.182, for cross-sectional area y = -7.102 + 0.520 × age ± 0.724 and y = -7.002 + 0.521 × age ± 0.726, and for volume y = -37.021 + 14.014 × ln(age) ± 1.091 and y = -37.425 + 14.197 × ln(age) ± 1.109., Conclusions: With no sex differences, the odontoid and body ossification centers of the axis grow logarithmically in transverse and sagittal diameters, and in volume, while proportionately in cross-sectional area. Our specific-age reference data for the odontoid and body ossification centers of the axis may be relevant for determining the fetal stage and maturity and for in utero three-dimensional sonographic detecting segmentation anomalies of the axis., Competing Interests: The authors declare that they have no conflict of interest.

Background: The odontoid process is a critical component of the cranio-cervical junction. Therefore, clinicians who diagnose, treat, or operate this region need a strong background in regard to the embryology, anatomy, and anatomical variations that may be seen for the odontoid process., Methods: A literature review was performed, using standard search engines, to explore the morphology, embryology, and anatomical variants of the odontoid process., Conclusions: 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.

Congenital spinal fusion of an odontoid process to an atlantal hemiarch is very rare. The unfamiliarity of the medical fraternity with this congenital malformation can easily be mistaken for an acute fracture, chronic infection or inflammatory disease. We present our experience of managing an adult who presented with neck pain after a motor vehicle accident. Radiological investigation revealed congenital fusion of the odontoid process to the atlantal hemiarch. The prevalence, embryology and clinical significance of this anomaly are discussed. As the natural progression of this anomaly is not well documented, we suggest periodic follow-up to monitor the progression of degenerative changes and instability of the occipitoatlantal junction., (2015 BMJ Publishing Group Ltd.)

Background: Knowledge of biomechanics and the cervical spine's anatomy has become more topical as the incidence of whiplash neck disorders has increased. Unfortunately, injuries after traffic accidents are often brought to court, where the medical expert's knowledge is of utmost importance to ensure a correct medical evaluation., Material and Methods: The article is based on information identified through non-systematic searches of PubMed and on the author's experience as a professor of anatomy., Results: The cervical spine is particularly vulnerable to forces perpendicular to the length axis. Stability depends largely on the soft tissue. Injuries of soft tissue (especially in ligaments and intervertebral discs) may lead to instability and periosteal reaction with subsequent new formation of bone., Interpretation: The cervical spine is a relatively weak and vulnerable part of the body. One should consider locally restricted new formations of tissue with corresponding height reduction of the intervertebral disc as a sign of genuine injury.

Aim: The aims of this clinical study were to describe the segments and the inferior boundaries of the odontoid process as regards the embryological development of C2 based on the magnetic resonance imaging finding., Material and Methods: Cranial and cervical magnetic resonance images including occiput, C1, and C2, and those obtained for different reasons such as evaluation of cranial and upper cervical pathology were re-evaluated for this study. Synchondroses around the odontoid process were accepted as the boundaries between the neural arch and the body of C2., Results: Thirty cases were included for this study. Fifteen of these were adult cases and the remaining 15 were in pediatric cases. Apicodental, dentocentral, neurocentral, and dentoneural synchondrotic articulations were clear, especially under the ages of 3 years. The dentocentral synchondrosis was found well below the line drawn through the level of superior articulating facets., Conclusion: This study demonstrated that the inferior boundary of the odontoid process is not located at the level of superior articulating facets. The real border between the odontoid process and the body of C2 is located well below the level of the superior articulating facets because of the location of the dentocentral synchondrotic articulation. This level should be considered in the classification of C2 fractures.

Abnormalities of the craniovertebral junction, most of which are associated with the occipital bone, are of interest not only to anatomists but also to clinicians because many of these deformities produce clinical symptoms. The occipital bone in humans is formed by the fusion of the sclerotomes corresponding to the roots of the hypoglossal nerve. In lower vertebrates, the cranial half of the first cervical sclerotome forms a separate bone between the atlas and occipital bone, the proatlas; in man it may contribute to anomalous structures around the foramen magnum. One such structure, a median occipital condyle, which exhibited an articular facet for the odontoid process, was observed in an adult male skull at the anterior margin of the foramen magnum. This anomaly is discussed in light of available literature., (Copyright 2002 Wiley-Liss, Inc.)

Os odontoideum (OO) and absentia odontoidei (AO) are rare conditions, which mainly are of interest because they may cause atlanto-axial instability. Traditionally they are considered to be congenital lesions. However, during the latest decades a number of acquired cases have been reported. Presently it is generally believed that the two conditions may exist in both a congenital and an acquired version. A review of the literature about OO fails to disclose any solid evidence in support of the classical theory of congenitality. It is concluded that OO and AO are diseases of childhood and adolescence. They are probably always acquired, and result from avascular necrosis of the odontoid process during the growth process.

Patterns of skeletal abnormality at the craniovertebral junction in the normal population and in syndromes such as Down, Morquio etc, are compared and the recent embryological data and comparative anatomy reviewed. The authors' view based on their own clinical and radiological experience is that the os odontoideum is the product of excessive movement at the time of ossification of the cartilaginous dens and is exactly analogous to the unfused Type II odontoid fracture. True hypoplasia of the odontoid peg is part of a wider segmentation defect associated with Klippel Feil, occipitalised atlas and/or basilar invagination; it is hardly ever associated with instability.

Anomalies of the atlantoaxial articulation are discussed with emphasis on os odontoideum. Normal and abnormal embryological and anatomical characteristics are described, as is their relevance upon stability of the upper cervical segments. This paper further discusses and reviews theories pertaining to the congenital and acquired forms of os odontoideum and a case report is presented. Some conclusions are drawn from the presented case report.

We reviewed the findings of CT and myelogram of cases of os odontoideum. The diagnosis was confirmed by conventional tomogram in all these cases. Four cases were further confirmed by trans-oral decompression. Cartilage was found between the os odontoideum and the odontoid process during operation in these 4 cases. Four of them had no history of trauma and 2 of them had an associated anomaly; one was Down's syndrome, and the other was barrel chest and congenital dislocation of hips. CT findings of os odontoideum in these cases were a constriction and/or a gap of bony structure between the os odontoideum and the odontoid process. Myelograms showed spinal stenosis as a result of atlanto-axial dislocation, or anterior extradural compression from overgrown cartilage and posteriorly dislocated tip of shortened odontoid process.

An odontoid bone was detected in an adult patient after injury to neck, with secondary appearance of disorders related to C1-C2 instability that disappeared after posterior C1-C2 arthrodesis. The odontoid bone is a rare anomaly of debatable origin. Current pathogenicity theories are discussed.