Early stages of development of the alar fascia (human specimens at 6-12 weeks of development).

In recent years, there has been much discussion concerning the cervical fasciae. The aim of this study is to confirm and to describe the development of the alar fascia as well as its relationship with nearby structures. Histological preparations of 25 human embryos (6-8 weeks of development) and 25 human fetuses (9-12 weeks of development) were studied bilaterally using a conventional optical microscope. Our study confirms the existence of the alar fascia and permits three stages to be established during its development. The initial stage (1st), corresponding to the 6th week of development (Carnegie stages 18-19), is characterized by the beginning of the alar fascia primordium in the retroesophageal space at the level of C7-T1. In the formation stage (2nd), corresponding to the 7th and 8th weeks of development (Carnegie stages 20-23), the alar fascia primordium grows upwards and reaches the level of C2-C3. In the maturation stage (3rd), beginning in the 9th week of development, the visceral, alar and prevertebral fasciae can be identified. The alar fascia divides the retrovisceral space (retropharyngeal and retroesophageal) into two spaces: one anterior (between the alar fascia and the visceral fascia and extending from C1 to T1, named retropharyngeal or retroesophageal space according to the level) and the other posterior (between the alar fascia and the prevertebral fascia, named danger space). We suggest that this latter space be named the retroalar space. This study suggests that alar fascia development is related to mechanical factors and that the alar fascia permits the sliding of the pharynx and the oesophagus during swallowing.

Correlations between morphology of cervical vertebrae and dental eruption.

The process of dental eruption is submitted to physiological and pathological variables. A series of discrepancies may occur, one of these being a disturbance between dental age and bone age. The assessment of bone age is best made with the cervical vertebral maturation (CVM) method, simplified by Baccetti et al. (2005). The sample studied consisted of 215 orthodontic patients. The dental age was assessed on the orthopantomograph radiographies and the bone age on the lateral cephalograms. For determining the bone age, CVM method was used. Considering dental age, most of the patients (50.2%) have a premature dental age compared to bone age, while patients with normal dental age (27.9%) and patients with late dental age (21.9%) have a lower frequency. The correlation between the dental age and the bone age of the patients shows that patients who have higher values of dental age also have higher values of bone age (p<0.001). The correlation between genders shows that female patients tend to have a higher average value of bone age in comparison to male patients (p<0.001). The authors conclude that assessing bone age based on the morphology of cervical vertebrae and correlating it with the dental age could be of great use in opting for a certain orthodontic treatment plan.

Embryology of the craniocervical junction and posterior cranial fossa, part I: Development of the upper vertebrae and skull.

Although the embryology of the posterior cranial fossa can have life altering effects on a patient, a comprehensive review on this topic is difficult to find in the peer-reviewed medical literature. Therefore, this review article, using standard search engines, seemed timely. The embryology of the posterior cranial fossa is complex and relies on a unique timing of various neurovascular and bony elements. Derailment of these developmental processes can lead to a wide range of malformations such as the Chiari malformations. Therefore, a good working knowledge of this embryology as outlined in this review of its bony architecture is important for those treating patients with involvement of this region of the cranium. Clin. Anat. 31:466-487, 2018. © 2018 Wiley Periodicals, Inc.

Tgif1 and Tgif2 Regulate Axial Patterning in Mouse.

Tgif1 and Tgif2 are transcriptional repressors that inhibit the transcriptional response to transforming growth factor ß signaling, and can repress gene expression by direct binding to DNA. Loss of function mutations in TGIF1 are associated with holoprosencephaly (HPE) in humans. In mice, embryos lacking both Tgif1 and Tgif2 fail to complete gastrulation, and conditional double null embryos that survive past gastrulation have HPE and do not survive past mid-gestation. Here we show that in mice of a relatively pure C57BL/6 strain background, loss of Tgif1 alone results in defective axial patterning and altered expression of Hoxc6. The primary defects in Tgif1 null embryos are the presence of extra ribs on the C7 vertebra, consistent with a posterior transformation phenotype. In addition we observed defective cervical vertebrae, primarily C1-C5, in both adult mice and embryos that lacked Tgif1. The combination of Tgif1 and Tgif2 mutations increases the severity and penetrance of the posterior transformation phenotype, without altering the type of defects seen. Similarly, exposure of Tgif1 mutant embryos to retinoic acid at E8.5 increased the severity and penetrance of the Tgif1 phenotype. This suggests that Tgif1 and Tgif2 regulate axial patterning and that reduced TGIF function sensitizes embryos to the effects of retinoic acid.

Developmental Patterning as a Quantitative Trait: Genetic Modulation of the Hoxb6 Mutant Skeletal Phenotype.

The process of patterning along the anterior-posterior axis in vertebrates is highly conserved. The function of Hox genes in the axis patterning process is particularly well documented for bone development in the vertebral column and the limbs. We here show that Hoxb6, in skeletal elements at the cervico-thoracic junction, controls multiple independent aspects of skeletal pattern, implicating discrete developmental pathways as substrates for this transcription factor. In addition, we demonstrate that Hoxb6 function is subject to modulation by genetic factors. These results establish Hox-controlled skeletal pattern as a quantitative trait modulated by gene-gene interactions, and provide evidence that distinct modifiers influence the function of conserved developmental genes in fundamental patterning processes.

[Contribution of the cervical vertebral maturation (CVM) method to dentofacial orthopedics: update]. / Intérêt de la méthode de maturation des vertèbres cervicales (CVM) en orthopédie dento-faciale : mise au point.

The successful orthopedic treatment of skeletal Class II malocclusions is closely related to the reasoned determination of the optimal time to initiate the treatment. This is why various methods have been proposed to assess skeletal maturation, such as a hand-wrist radiograph or the cervical vertebral maturation (CVM) method. The hand-wrist radiograph was up to now the most frequently used method to assess skeletal maturation. However, the clinical and biological limitations of this technique, as well as the need to perform an additional radiograph, were reasons to develop another method to explore the maturation stages of visible cervical vertebrae on a simple lateral cephalometric radiograph. The authors compare the 2 methods and prove the greater contribution of the CVM method compared to the hand-wrist radiograph.

Distribution of matrix proteins in perichondrium and periosteum during the incorporation of Meckel's cartilage into ossifying mandible in midterm human fetuses: an immunohistochemical study.

Immunohistochemical localization of versican and tenascin-C were performed; the periosteum of ossifying mandible and the perichondrium of Meckel's cartilage, of vertebral cartilage, and of mandibular condylar cartilage were examined in midterm human fetuses. Versican immunoreactivity was restricted and evident only in perichondrium of Meckel's cartilage and vertebral cartilage; conversely, tenascin-C immunoreactivity was only evident in periosteum. Therefore, versican and tenascin-C can be used as molecular markers for human fetal perichondrium and fetal periosteum, respectively. Meckel's cartilage underwent endochondral ossification when it was incorporated into the ossifying mandible at the deciduous lateral incisor region. Versican immunoreactivity in the perichondrium gradually became weak toward the anterior primary bone marrow. Tenascin-C immunoreactivity in the primary bone marrow was also weak, but tenascin-C positive areas did not overlap with versican-positive areas; therefore, degradation of the perichondrium probably progressed slowly. Meanwhile, versican-positive perichondrium and tenascin-C-positive periosteum around the bone collar in vertebral cartilage were clearly discriminated. Therefore, the degradation of Meckel's cartilage perichondrium during endochondral ossification occurred at a different rate than did degradation of vertebral cartilage perichondrium. Additionally, the perichondrium of mandibular condylar cartilage showed tenascin-C immunoreactivity, but not versican immunoreactivity. That perichondrium of mandibular condylar cartilage has immunoreactivity characteristic of other periosteum tissues may indicate that this cartilage is actually distinct from primary cartilage and representative of secondary cartilage.

Contribution of embryology in the understanding of cervical venous system anatomy within and around the transverse foramen: a review of the classical literature.

Anatomic arrangement of venous system within the transverse foramen is a controversial topic among authors. Precise knowledge of this arrangement is necessary in imaging where vertebral artery dissection is suspected, as well as in surgical approaches of cervical spine. This knowledge objective cannot be achieved without a prerequisite knowledge of primitive venous system. We present here an update on the development of the transverse foramen venous system through a literature review. Our review of the classical literature aimed at synthesis of available related embryological knowledge and relating this synthesis to cervical vertebrae anatomy. Our findings with regard to different primitive descriptions were consistent and often complementary across the studies. The description has varied from a single vertebral vein to a single vein divided at certain areas, or even to a confluence of venous plexus. In this manner, the embryonic knowledge for instance on venous system can help us to better understand the segmental development of vertebral veins and their plexus arrangement. Furthermore, the cranial-caudal embryology, in particular of the nervous system, conveys the initial plexiform arrangement of vertebral veins, which ends into a single venous trunk joining the subclavian vein.

Retinoic acid controls proper head-to-trunk linkage in zebrafish by regulating an anteroposterior somitogenetic rate difference.

During vertebrate development, the primary body axis elongates towards the posterior and is periodically divided into somites, which give rise to the vertebrae, skeletal muscles and dermis. Somites form periodically from anterior to posterior, and the anterior somites form in a more rapid cycle than the posterior somites. However, how this anteroposterior (AP) difference in somitogenesis is generated and how it contributes to the vertebrate body plan remain unclear. Here, we show that the AP difference in zebrafish somitogenesis originates from a variable overlapping segmentation period between one somite and the next. The AP difference is attributable to spatiotemporal inhibition of the clock gene her1 via retinoic acid (RA) regulation of the transcriptional repressor ripply1. RA depletion thus disrupts timely somite formation at the transition, eventually leading to the loss of one somite and the resultant cervical vertebra. Overall, our results indicate that RA regulation of the AP difference is crucial for proper linkage between the head and trunk in the vertebrate body plan.

Hoxa-5 acts in segmented somites to regulate cervical vertebral morphology.

The vertebrate axial skeleton (vertebral column and ribs) is derived from embryonic structures called somites. Mechanisms of somite formation and patterning are largely conserved along the length of the body axis, but segments acquire different morphologies in part through the action of Hox transcription factors. Although Hox genes' roles in axial skeletal patterning have been extensively characterized, it is still not well understood how they interact with somite patterning pathways to regulate different vertebral morphologies. Here, we investigated the role of Hoxa-5 in after somite segmentation in chick. Hoxa-5 mRNA is expressed in posterior cervical somites, and within them is restricted mainly to a sub-domain of lateral sclerotome. RNAi-based knockdown leads to cartilage defects in lateral vertebral elements (rib homologous structures) whose morphologies vary within and outside of the Hoxa-5 expression domain. Both knockdown and misexpression suggest that Hoxa-5 acts via negative regulation of Sox-9. Further, Hoxa-5 misexpression suggests that spatial and/or temporal restriction of Hoxa-5 expression is necessary for proper vertebral morphology. Finally, the restriction of Hoxa-5 expression to lateral sclerotome, which we hypothesize is important for its patterning function, involves regulation by signaling pathways that pattern somites, Fgf-8 and Shh.

New anatomical data on the growing C4 vertebra and its three ossification centers in human fetuses.

PURPOSE: Detailed knowledge on the normative growth of the spine is of great relevance in the prenatal diagnosis of its abnormalities. The present study was conducted to compile age-specific reference data for vertebra C4 and its three ossification centers in human fetuses. MATERIALS AND METHODS: With the use of CT (Biograph mCT), digital image analysis (Osirix 3.9) and statistical analysis (Wilcoxon signed-rank test, Kolmogorov-Smirnov test, Levene's test, Student's t test, one-way ANOVA, post hoc RIR Tukey test, linear and nonlinear regression analysis), the normative growth of vertebra C4 and its three ossification centers in 55 spontaneously aborted human fetuses (27 males, 28 females) aged 17-30 weeks was examined. RESULTS: Significant differences in neither sex nor laterality were found. The height and transverse and sagittal diameters of the C4 vertebral body increased logarithmically as: y = -3.866 + 2.225 × ln(Age) ± 0.238 (R(2) = 0.69), y = -7.077 + 3.547 × ln(Age) ± 0.356 (R(2) = 0.72) and y = -3.886 + 2.272 × ln(Age) ± 0.222 (R(2) = 0.73), respectively. The C4 vertebral body grew linearly in cross-sectional area as y = -7.205 + 0.812 × Age ± 1.668 (R(2) = 0.76) and four-degree polynomially in volume as y = 14.108 + 0.00007 × Age(4) ± 6.289 (R(2) = 0.83). The transverse and sagittal diameters, cross-sectional area and volume of the ossification center of the C4 vertebral body generated the following functions: y = -8.836 + 3.708 × ln(Age) ± 0.334 (R(2) = 0.76), y = -7.748 + 3.240 × ln(Age) ± 0.237 (R(2) = 0.83), y = -4.690 + 0.437 × Age ± 1.172 (R(2) = 0.63) and y = -5.917 + 0.582 × Age ± 1.157 (R(2) = 0.77), respectively. The ossification center-to-vertebral body volume ratio gradually declined with age. On the right and left, the neural ossification centers showed the following growth: y = -19.601 + 8.018 × ln(Age) ± 0.369 (R(2) = 0.92) and y = -15.804 + 6.912 × ln(Age) ± 0.471 (R (2) = 0.85) for length, y = -5.806 + 2.587 × ln(Age) ± 0.146 (R(2) = 0.88) and y = -5.621 + 2.519 × ln(Age) ± 0.146 (R(2) = 0.88) for width, y = -9.188 + 0.856 × Age ± 2.174 (R(2) = 0.67) and y = -7.570 + 0.768 × Age ± 2.200 (R(2) = 0.60) for cross-sectional area, and y = -13.802 + 1.222 × Age ± 1.872 (R(2) = 0.84) and y = -11.038 + 1.061 × Age ± 1.964 (R(2) = 0.80) for volume, respectively. CONCLUSIONS: The morphometric parameters of vertebra C4 and its three ossification centers show no sex differences. The C4 vertebral body increases logarithmically in height and both sagittal and transverse diameters, linearly in cross-sectional area, and four-degree polynomially in volume. The three ossification centers of vertebra C4 grow logarithmically in both transverse and sagittal diameters, and linearly in both cross-sectional area and volume. The age-specific reference intervals for evolving vertebra C4 may be useful in the prenatal diagnosis of congenital spinal defects.

Accessory transverse foramina in the cervical spine: incidence, embryological basis, morphology and surgical importance.

AIM: To study the incidence of accessory foramina transversaria in cervical spine and to analyze them morphologically with emphasize on their embryological and surgical importance. MATERIAL AND METHODS: The study included 363 human cervical vertebrae which were procured from the bone collections of the Department of Anatomy. The foramen transversarium was observed macroscopically on both sides of all the vertebras, the accessory foramina were noted. RESULTS: Out of 363 specimens, only 6 (1.6%) vertebrae showed the accessory foramina. Among them 5 (1.4%) vertebra had double foramina and only 1 (0.3%) vertebra showed three foramina. Only 1 (0.3%) vertebrae showed the foramen on both sides and the remaining 5 (1.4%) had unilateral foramina. Among the unilateral, 4 were present on the right side and only 1 was on the left side. No vertebrae showed the absence of foramen transversarium. CONCLUSION: The present study observed the accessory foramina transversarium in 1.6% of cases. The unilateral presence was more common than the bilateral. The surgical anatomy of these variations is important for the neurosurgeons and radiologists for interpreting the computed tomogram and magnetic resonance image scans. Their morphological knowledge is clinically important since the course of the vertebral artery may be distorted in such situations.

Fetal anatomy of the lower cervical and upper thoracic fasciae with special reference to the prevertebral fascial structures including the suprapleural membrane.

The aim of this study was to find basic rules governing the fetal anatomy of the deep cervical fasciae and their connections to the mediastinal fasciae. We examined the histology of paraffin-embedded preparations of 18 mid-term fetuses (5 between 9 and 12 weeks of gestation, 3 between 15 and 18 weeks, and 10 between 20 and 25 weeks). The prevertebral lamina of the deep cervical fasciae (PLDCF) developed as an intermediate aponeurosis for the bilateral bellies of the longus colli muscles. In contrast, the alar fascia developed as a connecting band between the bilateral adventitiae of the common carotid artery. The retropharyngeal fascia became evident much later than the latter two fasciae. The fascia covering the thymus was thicker than the fascia for the strap muscles (the pretracheal lamina of the cervical fascia). The primitive suprapleural membrane, or Sibson's fascia, contained veins and fatty tissues, and was composed of the alar fascia rather than the PLDCF, tranversalis fascia, or endothoracic fascia. The prevertebral two-laminar configuration was rather evident in the early stages of development because, in the later stages, the fasciae together provided a multilaminar structure, especially in the lateral area in front of the longus colli, which suspended the cupula pleurae. To consider a continuation from the base of the neck to the upper mediastinum, the alar fascia seems to be a key structure for connecting the vascular sheath to the parietal pleura.

Formation of the vertebral arches of the cervical, thoracic and lumbar vertebrae in early human foetuses.

Fusion of the neural arches was studied in 6 serially sectioned human foetuses aged 9 and 10 weeks. In foetuses of 9 weeks, the completion of arches was observed in the cervical, upper thoracic, and middle thoracic regions of the vertebral column. During the 10th week of development, fusion of neural processes progresses in the lower thoracic and upper three lumbar vertebrae.

Transgenic over-expression of growth differentiation factor 11 propeptide in skeleton results in transformation of the seventh cervical vertebra into a thoracic vertebra.

Growth differentiation factor 11 (GDF11) is one of the significant genes that control skeletal formation. Knockout of GDF11 function causes abnormal patterning of the anterior/posterior axial skeleton. The mRNA of GDF11 is initially translated to a precursor protein that undergoes a proteolytic cleavage to generate the C-terminal peptide or mature GDF11, and the N-terminal peptide named GDF11 propeptide. The propeptide can antagonize GDF11 activity in vitro. To investigate the effects of GDF11 propeptide on GDF11 function in vivo, we generated transgenic mice that over-express the propeptide cDNA in skeletal tissue. The transgenic mice showed formation of extra ribs on the seventh cervical vertebra (C7) as a result of transformation of the C7 vertebra into a thoracic vertebra. The GDF11 propeptide transgene mRNA was detected in tail tissue in embryos and was highly expressed in tail and calvaria bones after birth. A high frequency of C7 rib formation was noticed in the transgenic mouse line with a high level of transgene expression. The anterior boundaries of Hoxa-4 and Hoxa-5 mRNA in situ expressions showed cranial shifts from their normal prevertebra locations in transgenic embryos. These results demonstrated significant effects of GDF11 propeptide transgene on vertebral formation, which are likely occurring through depressing GDF11 function and altered locations of Hoxa-4 and Hoxa-5 expression.

From fetus to adult--an allometric analysis of the giraffe vertebral column.

As mammalian cervical vertebral count is almost always limited to seven, the vertebral column of the giraffe (Giraffa camelopardalis) provides an interesting study on scaling and adaptation to shape in light of these constraints. We have defined and described the growth rates of the lengths, widths, and heights of the vertebrae from fetal through neonatal life to maturity. We found that the disproportionate elongation of the cervical vertebrae is not a fetal process but occurs after birth, and that each cervical (C2-C7) vertebrae elongates at the same rate. C7 is able to specialize toward elongation as its function has been shifted to T1. We concluded that T1 is a transitional vertebra whose scaling exponent and length is between that of the cervical and thoracic series. Despite its transitional nature, T1 is still regarded as thoracic, as it possesses an articulating rib that attaches to the sternum. The other dimensions taken (width, height, and spinous process length) show that giraffe vertebral morphology exhibit adaptations to biomechanical strain, and we have underlined the importance of the thoracic spinous processes in supporting the head and neck.

[Anatomy of the cervical spine]. / Cervikalcolumnas anatomi.

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.

Orthodontics and foetal pathology: a personal view on craniofacial patterning.

This article summarizes the essentials of studies on the craniofacial skeleton performed over 17 years. It presents data from research into foetal pathology resulting in new views on craniofacial patterning and/or fields for further discussion. The fields described cover all areas seen on profile, frontal, and panoramic radiographs. The fields are the theca, frontonasal, maxillary, palatine, and mandibular together with the cerebellar field and cervical spine. Regional fields in the dentition are described according to the pattern of peripheral nerve innervation. Studies on severely malformed foetuses show that the malformation can occur solely within a single field or in several fields. This is the background for these personal views on craniofacial patterning. These new views may assist in the diagnosis and interpretation of malformations in the cranium and dentition.

In ovo application of antagomiRs indicates a role for miR-196 in patterning the chick axial skeleton through Hox gene regulation.

Patterning of the vertebrate axial skeleton requires precise spatial and temporal control of Hox gene expression during embryonic development. MicroRNAs (miRNAs) are recently described modulators of gene activity, and members of the miR-196 and miR-10 families have been shown to target several Hox genes in vivo. Testing miRNA function in mice is complicated by potential redundancy between family members. To circumvent this, we have developed protocols for introducing modified antisense oligonucleotides (antagomiRs) in ovo during chick development. Using this approach, we identify a layer of regulatory control provided by the miR-196 family in defining the boundary of Hox gene expression along the anterior-posterior (A-P) embryonic axis. Following knockdown of miR-196, we observe a homeotic transformation of the last cervical vertebrae toward a thoracic identity. This phenotypic alteration is, in part, due to an anterior expansion of Hoxb8 gene expression and consolidates the in vivo relevance of post-transcriptional Hox gene regulation provided by miRNAs in the complex hierarchies governing axial pattering.

Lack of the mesodermal homeodomain protein MEOX1 disrupts sclerotome polarity and leads to a remodeling of the cranio-cervical joints of the axial skeleton.

Meox1 and Meox2 are two related homeodomain transcription factor genes that together are essential for the development of all somite compartments. Here we show that mice homozygous for Meox1 mutations alone have abnormalities that are restricted to the sclerotome and its derivatives. A prominent and consistent phenotype of these mutations is a remodeling of the cranio-cervical joints whose major feature is the assimilation of the atlas into the basioccipital bone so that the skull rests on the axis. These abnormalities can be traced back to changes in the relative rates of cell proliferation in the rostral and caudal sclerotome compartments, and they are associated with alterations in the expression of at least three transcription factor genes, Tbx18, Uncx, and Bapx1. As previously observed for Bapx1, MEOX1 protein occupies evolutionarily conserved promoter regions of Tbx18 and Uncx, suggesting that Meox1 regulates these genes at least in part directly. Hence, Meox1 is part of a regulatory circuit that serves an essential, non-redundant function in the maintenance of rostro-caudal sclerotome polarity and axial skeleton formation.