Musculoskeletal System - Skull Development: Difference between revisions
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* '''compound craniosynostosis''' premature suture fusion involving two or more sutures. | * '''compound craniosynostosis''' premature suture fusion involving two or more sutures. | ||
* '''craniosynostosis''' - (craniostenosis) the premature fusion of cranial sutures. | * '''craniosynostosis''' - (craniostenosis) the premature fusion of cranial sutures. | ||
* '''dermatocranium''' - (membranous) skull calvarial vault develops from intramembranous ossification. | |||
* '''harlequin eye''' - a term used to describe the prominent bilateral elliptical orbits of the skull seen in brachycephaly. | * '''harlequin eye''' - a term used to describe the prominent bilateral elliptical orbits of the skull seen in brachycephaly. | ||
* '''endochondral ossification''' - bone formation from a pre-existing cartilage template, such as the chondrocranium. | * '''endochondral ossification''' - bone formation from a pre-existing cartilage template, such as the chondrocranium. |
Revision as of 11:09, 22 March 2016
Embryology - 26 Jun 2024 Expand to Translate |
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Introduction
The Skull is a unique skeletal structure in several ways: embryonic cellular origin (neural crest), form of ossification (intramembranous and endochondrial) and flexibility (fibrous sutures). The cranial vault (which encloses the brain) bones are formed by intramembranous ossification. While the bones that form the base of the skull are formed by endochondrial ossification. The bones enclosing the brain have large flexible fibrous joints (sutures) which allow firstly the head to pass through the birth canal and secondly postnatal brain growth. (See also notes on Head Development)
In humans, ossification continues postnatally, through puberty until mid 20's and in old age the sutures separating the vault plates are often completely ossified.
In the entire skeleton, early ossification occurs in the jaw and at the ends of long bones (More? see movie developing mouse). Osteoblasts manufacture bone and are derived from ectomesenchymal in origin. (More? see lineage below). Flexible fibrous sutures allow growth of the brain to be accomodated by calvarial plate growth. Recent studies have show that noggin (a BMP antagonist) is involved in closure of these sutures.
Developmentally and clinically there are several abnormalities associated with skull growth and palate development. These abnormalities can furthermore impact on other systems such as neural, sensory, respiratory and nutritional functions.
Category:Skull | Head Development | Palate Development | Temporomandibular Joint
Historic Embryology |
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1910 Textbook Skull | 1910 Textbook Skull Images | 1910 30mm Embryo Skull | 1921 Human Brain Vascular | 1923 Head Subcutaneous Plexus | 1919 21mm Embryo Skull | 1920 Human Embryo Head Size | 1921 43 mm Fetal Skull | 1915 The Monotreme Skull | Historic Disclaimer |
Some Recent Findings
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More recent papers |
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This table allows an automated computer search of the external PubMed database using the listed "Search term" text link.
More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Skull Embryology <pubmed limit=5>Skull Embryology</pubmed> |
Fetal Skull
The Images below show the combined endochondral and intramembranous ossification that is occurring in early fetal development (week 12).
In the first 2 images the bone cartilage is shown in blue and the new bone in red.
Note the difference in appearance between the upper and lower jaw (maxilla and mandible), the currently cartilage base of the skull (chondrocranium) and the cranial vault (neurocranium).
Fetal head lateral view |
Fetal head medial view |
Fetal head section |
This mid-line section through the fetal head shows features of the developing skull and the brain, face and mouth.
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Mandible Development
Meckel's cartilage, located within the first pharyngeal arch mandibular prominence, forms a cartilage "template" besides which the mandible develops by the process of intramembranous ossification. It is important to note that this cartilage template does not ossify (endochondral ossification) but provides a transient structure where the mandible will form, and later degenerates.
Embryonic and Fetal Mandible
Embryo CRL 24 mm (outer aspect, about Carnegie stage 22)
Embryo CRL 24 mm (inner aspect, about Carnegie stage 22)
Embryo CRL 95 mm (outer aspect, about Fetal week 12, GA week 14)
Embryo CRL 95 mm (inner aspectt, about Fetal week 12, GA week 14)
Birth to Adult Mandible
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Animated GIF |
- Mandible Development: Week 8 outer view | Week 8 inner view | Week 12 outer view | Week 12 inner view | Week 12 Head outer view | Week 12 Head inner view | Birth | Childhood | Adult | Old Age | Small Animation | Large Animation | Muscle Attachments | Mandible Ossification | 1909 Mandible | embryo 18 mm | embryo 24 mm | embryo 28 mm | fetus 43 mm | fetus 65 mm | fetus 55 mm | fetus 95 mm | human 18-24-95 mm | Skull Development | Head Development
Neurocranium
Frontal bone
- neural crest origin
- requires Msx1 and Dlx5[5]
Parietal bone
- paraxial mesoderm origin
Skull Views
anterior view | superior view | lateral view | lateral view |
showing anterior fontenelle, sutures, mandible | showing anterior fontenelle, sutures | showing suture, mandible | newborn skull |
Skull Fontanels and Sutures
The bones enclosing the brain have large flexible fibrous joints (sutures) which allow firstly the head to compress and pass through the birth canal and secondly to postnatally expand for brain growth. (More? Molecular Skull Sutures) These sutures gradually fuse at different times postnatally, firstly the metopic suture in infancy and the others much later. Abnormal fusion (synostosis) of any of the sutures will lead to a number of different skull defects, leading to disruption of brain development. (More? Abnormal Synostosis) In old age all these sutures are generally completely fused and ossified.
Skull Fontanels
The newborn skull has 6 fontanels (fontanelles) the most obvious are the anterior and posterior fontanels that close at different times postnatally.
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Newborn Skull Fontanels (CT, vertex view) |
At the molecular level, accelerated suture intramembranous ossification can be mediated through a dual role of β-catenin in both the expansion of osteoprogenitors and the maturation of osteoblasts.[6] These researchers also show that disruption of Axin2/β-catenin signaling alters the regulation of the downstream transcription target, cyclin D1, in the canonical Wnt pathway.[7]
Computed Tomography Views
Skull CT Vertex, later and basal views.[8] |
Sutures and Fontanels
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coronal suture
lambdoid suture
metopic suture begins at nose and runs superiorly to meet sagittal suture and fuses during infancy (fusion beginning at 3 months and completes by 6 to 8 months of age) before all other cranial sutures.
sagittal suture
Cranial Base Synchondroses
In the base of the skull there can also be found a number of synchondrosis, "cartilage sutures", that are the last to close and have a role in the ongoing growth of the postnatal skull. Synchondrosis is a type of cartilaginous joint in which the cartilage is usually converted into bone before adult life. It has been compared in appearance to a long bone growth plate, but is bipolar rather than unipolar in structure.
These sutures also lost at different times in postnatal development:
- Inter-sphenoidal – around birth
- Spheno-ethmoidal – 6-7 yrs
- Spheno-occipital – 12-15 yrs
Fetal Head Growth
Abnormalities
There are several skull deformities caused by premature fusion (synostosis) of different developing skull sutures. Suture abnormalities are classified as either "simple" (only one suture involved) or "compound" (two or more sutures involved).
* craniosynostosis premature cranial suture fusion, results in an abnormal skull shape, blindness and mental retardation.
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Craniosynostosis
Attenuation of signaling pathways stimulated by pathologically activated FGF-receptor 2 mutants prevents craniosynostosis.[9] "Craniosynostosis, the fusion of one or more of the sutures of the skull vault before the brain completes its growth, is a common (1 in 2,500 births) craniofacial abnormality, approximately 20% of which occurrences are caused by gain-of-function mutations in FGF receptors (FGFRs). ...These experiments show that attenuation of FGFR signaling by pharmacological intervention could be applied for the treatment of craniosynostosis or other severe bone disorders caused by mutations in FGFRs that currently have no treatment."
Dolichocephaly and scaphocephaly
Dolichocephaly and scaphocephaly
(premature fusion of the sagittal suture) |
Brachycephaly and anterior plagiocephaly
(Greek, brakhu = short) (Greek plagios = oblique)
- brachycephaly - premature bicoronal fusion
- anterior plagiocephaly - unicoronal fusion
Leads to a restriction of anterior-posterior calvarial growth and relatively unaffected biparietal growth.
Skull Turricephaly
Skull Trigonocephaly
(Greek, trigonos = three angles) This abnormality results from the premature fusion of the metopic suture occurring before 6 months (3-9 months) of age.
Skull Oxycephaly
Images show oxycephaly from severe sagittal and coronal synostoses (arrowheads).
Craniofrontonasal Syndrome
Craniofrontonasal syndrome (CFNS) is a human X-linked developmental disorder caused by a mutation in ephrin-B1 affecting mainly females. Characterised by abnormal development of cranial and nasal bones, craniosynostosis (premature coronal suture fusion), and other extracranial anomalies (limb polydactyly and syndactyly).
(a) Facial view showing marked hypertelorism, divergent squint, and central nasal groove (subject age, 1 year).
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Craniofrontonasal syndrome[10] | Links: OMIM - Craniofrontonasal Syndrome |
Skull Histology
A histological image of a skull bone formation by Intramembranous ossification.
Adult Skull
Adult Skull MRI | Links: | Skull Development | - MRI | ||||||||||||
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References
- ↑ <pubmed>22693558</pubmed>
- ↑ <pubmed>19605684</pubmed>
- ↑ <pubmed>19595791</pubmed>
- ↑ <pubmed>17132737</pubmed>| PNAS Link
- ↑ <pubmed>20824629</pubmed>
- ↑ <pubmed>17113065</pubmed>
- ↑ <pubmed>21108844</pubmed>
- ↑ 8.0 8.1 <pubmed>21431034</pubmed>| PMC3056371 | Indian J Radiol Imaging.
- ↑ <pubmed>17132737</pubmed>
- ↑ <pubmed>15166289</pubmed>| PNAS Link
Reviews
<pubmed>1522265</pubmed> <pubmed>9482048</pubmed> <pubmed>7813156</pubmed> <pubmed>7813157</pubmed> <pubmed>8266985</pubmed>
Articles
<pubmed>14504503</pubmed>
Search PubMed
Search July 2010 "Skull Development" All (15473) Review (1231) Free Full Text (1634)
Search Pubmed: Skull Development
Additional Images
Historic Images
1910 Development of the Skeleton |
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1921 43 mm Fetal Skull |
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1918 Gray's Anatomy |
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Terms
- anterior fontanel - developing skull region that closes by about 20 months postnatally.
- basion - anatomical region on the basiocciput located at the midpoint between the anterior margin and posterior margin (opisthion) of the foramen magnum.
- compound craniosynostosis premature suture fusion involving two or more sutures.
- craniosynostosis - (craniostenosis) the premature fusion of cranial sutures.
- dermatocranium - (membranous) skull calvarial vault develops from intramembranous ossification.
- harlequin eye - a term used to describe the prominent bilateral elliptical orbits of the skull seen in brachycephaly.
- endochondral ossification - bone formation from a pre-existing cartilage template, such as the chondrocranium.
- intramembranous ossification - bone formation from a membrane where no pre-existing cartilage is found, such as the calvarial vault component.
- neurocranium - the portion of the skull that surrounds the brain. Ossification of bones in cranial base (endochondral) and vault (intramembranous).
- opisthion - anatomical region located on the occipital bone, located at the midpoint of the posterior margin of the foramen magnum.
- posterior fontanel - developing skull region that closes by about 3 months postnatally.
- primary craniosynostosis - an intrinsic defect in a suture.
- secondary craniosynostosis - premature closure of normal sutures due to systemic and metabolic (hyperthyroidism, hypercalcemia, hypophosphatasia, vitamin D deficiency, renal osteodystrophy, Hurler's Syndrome, sickle cell disease and thalassemia) and those that can affect brain growth.
- simple craniosynostosis - premature fusion involving only one suture.
- synostosis - premature fusion.
- viscerocranium - facial skeleton and some anterior neck structures.
External Links
External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.
- PubMed Health Craniosynostosis
Glossary Links
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Cite this page: Hill, M.A. (2024, June 26) Embryology Musculoskeletal System - Skull Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Musculoskeletal_System_-_Skull_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G