Development and growth of the craniocervical junction with special reference to topographical relationship between the occipital basion, the anterior arch of atlas, and the odontoid process of axis: A study using human fetuses.

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.

Arcuate Foramen: Anatomy, Embryology, Nomenclature, Pathology, and Surgical Considerations.

BACKGROUND: The arcuate foramen is an anatomic variant that is thought to arise from ossification of the posterior atlanto-occipital membrane. Owing to potential entrapment of the vertebral artery segment that traverses the foramen, vertebrobasilar ischemia may occur, and the person may experience vertigo, headache, or neck pain. METHODS: We reviewed the literature regarding anatomy (both human and comparative), embryology, nomenclature, pathology, and surgery of the arcuate foramen. RESULTS: Surgically, the presence of an arcuate foramen is important when placing screws into lateral masses of the atlas. In these cases, the screws can damage the V3 segment of the vertebral artery and/or the suboccipital nerve. CONCLUSIONS: It is important to review the current literature on the arcuate foramen to further understand its morphology and clinical relevance.

What the mind does not know, the eyes do not see: a rare congenital fusion of the odontoid process to the atlantal hemiarch.

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.

[Spinal stenosis at the level of atlas in a boy with Down syndrome. A case report and literature review]. / Estenosis de canal a nivel del atlas en un niño con síndrome de Down. Presentación de un caso y revisión de la literatura.

INTRODUCTION: The appearance of congenital anomalies at the level of atlas is frequent in patients with neural alterations, as well as in the Down syndrome. The presence of clinical stenosis for alteration in the posterior arch of C1 without a previous atlantoaxial subluxation hasn't been described in the literature thus far. CASE REPORT: We report an exceptional case of myelopathy due to compression at the level of the atlas in a 5-year-old boy with Down syndrome provoked by a developmental anomaly of the posterior arch of C1. A posterior laminectomy was achieved at that level with improvement of the previous symptoms. CONCLUSIONS: We have to pay special attention in children with syndromes associated with chondrogenesis alterations, as in the case of those with Down syndrome, to benefit from early treatment, since in most of the time they are diagnosed when symptoms are very severe.

Congenital posterior atlas defect associated with anterior rachischisis and early cervical degenerative disc disease: a case study and review of the literature.

A rare case of a wide congenital atlas defect is reported. A 25 year-old woman was admitted after complaints of radicular pain in the right arm. Radiographs incidentally revealed aplasia of the posterior arch of the atlas together with anterior rachischisis. A review of the literature is presented and a possible association with early disc degeneration is discussed.

Estimation of fetal age from dimensions of atlas and axis ossification centers.

The atlas and axis ossification centers of 106 human fetal and neonate skeletons were measured. The skeletons belong to the collection in the Department of Forensic Medicine of the Albert Szent-Györgyi Medical University, Szeged, Hungary. The age of the skeletons ranged from 4 to 10 lunar months. Nine linear measurements on the atlas, seven on the axis neural arches ossification centers and three on each one of the axis centra ossification centers were taken. We did simple and multiple linear regression analysis to estimate the age of fetuses. The results show that it is possible to use regression equations to estimate the fetal body length and age from atlas and axis ossification centers measurements during the whole period of development studied. The study of size and shape of the ossification centers using factorial analysis (principal component analysis) shows that the shape of the dens of the axis might be useful to estimate fetal viability.

A rare, complex developmental anomaly of the atlas: embryological and radiological considerations.

We report a patient with disseminated malignancy and a complex anomaly of C1 and C2 in whom CT confirmed the developmental nature of the bony abnormalities.

Mice with targeted disruptions in the paralogous genes hoxa-3 and hoxd-3 reveal synergistic interactions.

The Hox genes encode transcription factors which mediate the formation of the mammalian body plan along the anteroposterior and appendicular axes. Paralogous Hox genes within the separate linkage groups are closely related with respect to DNA sequence and expression, suggesting that they could have at least partially redundant functions. We showed previously that mice homozygous for independent targeted disruptions in the paralogous genes hoxa-3 and hoxd-3 had no defects in common. But our current analysis of double mutants has revealed strong, dosage-dependent interactions between these genes. We report here that in hoxd-3- homozygotes the first cervical vertebra, the atlas, is homeotically transformed to the adjacent anterior structure. Unexpectedly, in double mutants, rather than observing a more extensive homeotic transformation, the entire atlas is deleted. These observations are interpreted in terms of a model in which these Hox genes differentially regulate the proliferation rates of the appropriate sets of precursor cells.

Craniovertebral anomalies.

We have tried to clarify this confusing area by demonstrating the common relationships of these abnormalities. The development of the craniovertebral junction was present in order to understand the formation of the anomalies discussed. The radiologic lines and measurements that have been described are actually to measure the degree of compromise of the functional size of the foramen magnum. This mechanical compromise, either from direct neural compression and/or from a secondary vascular impairment (arterial or venous), leads to the signs and symptoms of cervicomedullary compression.