Earlier Evidence of Spheno-Occipital Synchondrosis Fusion Correlates with Severity of Midface Hypoplasia in Patients with Syndromic Craniosynostosis:

Mystery of the Muenke midface: spheno-occipital synchondrosis fusion and craniofacial skeletal patterns

PURPOSE

The spheno-occipital synchondrosis (SOS) is an important site of endochondral ossification in the cranial base that closes prematurely in Apert, Crouzon, and Pfeiffer syndromes, which contributes to varying degrees of midface hypoplasia. The facial dysmorphology of Muenke syndrome, in contrast, is less severe with low rates of midface hypoplasia. We thus evaluated the timing of SOS fusion and cephalometric landmarks in patients with Muenke syndrome compared to normal controls.

METHODS

Patients with Muenke syndrome who had at least one fine-cut head computed tomography scan performed from 2000 to 2020 were retrospectively reviewed. A case-control study was performed of patient scans and age- and sex-matched control scans. SOS fusion status was evaluated as open, partially closed, or closed.

RESULTS

We included 28 patients and compared 77 patient scans with 77 control scans. Kaplan-Meier analysis demonstrated an insignificantly earlier timeline of SOS fusion in Muenke syndrome (p = 0.300). Mean sella-orbitale (SO) distance was shorter (44.0 ± 6.6 vs. 47.7 ± 6.7 mm, p < 0.001) and mean sella-nasion-Frankfort horizontal (SN-FH) angle was greater (12.1° ± 3.8° vs. 10.1° ± 3.2°, p < 0.001) in the Muenke group, whereas mean sella-nasion-A point (SNA) angle was similar and normal (81.1° ± 5.7° vs. 81.4° ± 4.7°, p = 0.762).

CONCLUSION

Muenke syndrome is characterized by mild and often absent midfacial hypoplasia, with the exception of slight retropositioning of the infraorbital rim. Interestingly, SOS fusion patterns in these patients are not significantly different from age- and sex-matched controls despite an increased odds of fusion. It is possible that differences in timing of SOS fusion may manifest phenotypically at the infraorbital rim rather than at the maxilla.

Feasibility of spheno-occipital synchondrosis fusion stages as an indicator for the assessment of maxillomandibular growth: A mixed longitudinal study

OBJECTIVES

This study aimed to assess the relative growth rates (RGRs) of the maxilla and mandible at varying fusion stages of the spheno-occipital synchondrosis (SOS), thereby elucidating the potential of SOS stages in predicting maxillomandibular growth.

MATERIALS AND METHODS

A total of 320 subjects (171 boys and 149 girls), aged 6 to 18 years, were retrospectively included. Each subject had a minimum of two longitudinal cone-beam computed tomography (CBCT) images, with no more than one interval of SOS fusion stage change between the two scans. Subjects were categorized based on their SOS fusion stages and genders. The RGRs of the maxilla and mandible at various SOS fusion stages were measured and compared using longitudinal CBCT images.

RESULTS

Significant statistical differences were observed in maxillomandibular RGRs across various SOS fusion stages. In girls, the sagittal growth of the maxilla remained stable and active until SOS 3, subsequently exhibited deceleration in SOS 4-5 (compared to SOS 3-4, P < .05) and continued to decrease in SOS 5-6. Whereas in boys, the sagittal growth of the maxilla remained stable until SOS 4, and a deceleration trend emerged starting from SOS 5 to 6 (P < .01 compared to SOS 4-5). Mandibular growth patterns in both genders exhibited a progression of increasing-accelerating-decelerating rates from SOS 2 to 6. The highest RGRs for total mandibular length were observed in SOS 3-4 and SOS 4-5.

CONCLUSION

Spheno-occipital synchondrosis fusion stages can serve as a valid indicator of maxillomandibular growth maturation.

3D atlas of the human fetal chondrocranium in the middle trimester

The chondrocranium provides the key initial support for the fetal brain, jaws and cranial sensory organs in all vertebrates. The patterns of shaping and growth of the chondrocranium set up species-specific development of the entire craniofacial complex. The 3D development of chondrocranium have been studied primarily in animal model organisms, such as mice or zebrafish. In comparison, very little is known about the full 3D human chondrocranium, except from drawings made by anatomists many decades ago. The knowledge of human-specific aspects of chondrocranial development are essential for understanding congenital craniofacial defects and human evolution. Here advanced microCT scanning was used that includes contrast enhancement to generate the first 3D atlas of the human fetal chondrocranium during the middle trimester (13 to 19 weeks). In addition, since cartilage and bone are both visible with the techniques used, the  endochondral ossification of cranial base was mapped since this region is so critical for brain and jaw growth. The human 3D models are published as a scientific resource for human development.

Genetic Subtypes of Apert Syndrome Are Associated With Differences in Airway Morphology and Early Upper Airway Obstruction

BACKGROUND

Apert syndrome is predominantly caused by 2 paternally inherited gain-of-function mutations in the FGFR2 gene, Pro253Arg, and Ser252Trp. Studies comparing phenotypic features between these 2 mutations have established differences in syndactyly severity and incidence of cleft palate. Obstructive sleep apnea can be debilitating in a subset of patients with Apert syndrome, yet is not well understood. This study aims to determine whether FGFR2 mutations impart differential effects on airway physiology and morphology.

METHODS

Patients with Apert syndrome and confirmatory molecular testing were reviewed for polysomnography, nasal endoscopy, microlaryngoscopy and bronchoscopy, and computed tomography imaging. Obstructive apnea-hypopnea index and oxygen saturation nadir, nasal airway volumes, choanal cross-sectional area, and midfacial cephalometric dimensions were compared across mutation types.

RESULTS

Twenty-four patients (13 Ser252Trp, 11 Pro253Arg) were included. Severe obstructive sleep apnea (obstructive apnea-hypopnea index>10) occurred in 8 (62%) patients with Ser252Trp mutations compared with 1 (9%) patient with Pro253Arg mutations ( P =0.009). Computed tomography imaging at 1 year of age demonstrated that nasopharyngeal airway volumes were 5302±1076 mm 3 in the Ser252Trp group and 6832±1414 mm 3 in the Pro253Arg group ( P =0.041). Maxillary length (anterior nasal spine-posterior nasal spine, P =0.026) and basion-anterior nasal spine ( P =0.007) were shorter in patients with Ser252Trp mutations.

CONCLUSIONS

The findings suggest that the Ser252Trp mutation in Apert syndrome is associated with higher severity obstructive sleep apnea and decreased nasopharyngeal airway volume. Heightened clinical awareness of these associations may inform treatment planning and family counseling.

Craniofacial growth and function in achondroplasia: a multimodal 3D study on 15 patients

BACKGROUND

Achondroplasia is the most frequent FGFR3-related chondrodysplasia, leading to rhizomelic dwarfism, craniofacial anomalies, stenosis of the foramen magnum, and sleep apnea. Craniofacial growth and its correlation with obstructive sleep apnea syndrome has not been assessed in achondroplasia. In this study, we provide a multimodal analysis of craniofacial growth and anatomo-functional correlations between craniofacial features and the severity of obstructive sleep apnea syndrome.

METHODS

A multimodal study was performed based on a paediatric cohort of 15 achondroplasia patients (mean age, 7.8 ± 3.3 years), including clinical and sleep study data, 2D cephalometrics, and 3D geometric morphometry analyses, based on CT-scans (mean age at CT-scan: patients, 4.9 ± 4.9 years; controls, 3.7 ± 4.2 years).

RESULTS

Craniofacial phenotype was characterized by maxillo-zygomatic retrusion, deep nasal root, and prominent forehead. 2D cephalometric studies showed constant maxillo-mandibular retrusion, with excessive vertical dimensions of the lower third of the face, and modifications of cranial base angles. All patients with available CT-scan had premature fusion of skull base synchondroses. 3D morphometric analyses showed more severe craniofacial phenotypes associated with increasing patient age, predominantly regarding the midface-with increased maxillary retrusion in older patients-and the skull base-with closure of the spheno-occipital angle. At the mandibular level, both the corpus and ramus showed shape modifications with age, with shortened anteroposterior mandibular length, as well as ramus and condylar region lengths. We report a significant correlation between the severity of maxillo-mandibular retrusion and obstructive sleep apnea syndrome (p < 0.01).

CONCLUSIONS

Our study shows more severe craniofacial phenotypes at older ages, with increased maxillomandibular retrusion, and demonstrates a significant anatomo-functional correlation between the severity of midface and mandible craniofacial features and obstructive sleep apnea syndrome.

Craniofacial dysmorphology in Down syndrome is caused by increased dosage of Dyrk1a and at least three other genes

Down syndrome (DS), trisomy of human chromosome 21 (Hsa21), occurs in 1 in 800 live births and is the most common human aneuploidy. DS results in multiple phenotypes, including craniofacial dysmorphology, which is characterised by midfacial hypoplasia, brachycephaly and micrognathia. The genetic and developmental causes of this are poorly understood. Using morphometric analysis of the Dp1Tyb mouse model of DS and an associated mouse genetic mapping panel, we demonstrate that four Hsa21-orthologous regions of mouse chromosome 16 contain dosage-sensitive genes that cause the DS craniofacial phenotype, and identify one of these causative genes as Dyrk1a. We show that the earliest and most severe defects in Dp1Tyb skulls are in bones of neural crest (NC) origin, and that mineralisation of the Dp1Tyb skull base synchondroses is aberrant. Furthermore, we show that increased dosage of Dyrk1a results in decreased NC cell proliferation and a decrease in size and cellularity of the NC-derived frontal bone primordia. Thus, DS craniofacial dysmorphology is caused by an increased dosage of Dyrk1a and at least three other genes.

Effect of Bone-Borne Trans -Sutural Distraction Osteogenesis Therapy on the Cranial Base of Children With Midfacial Hypoplasia Due to Cleft Lip and Palate

Bone-borne trans -sutural distraction osteogenesis (TSDO) is widely used to treat midfacial hypoplasia in children with cleft lip and palate; however, its effects on the cranial base are still poorly understood. The authors aimed to study morphological changes in the cranial base after TSDO. Pre and postoperative computed tomography (CT) images of cleft lip and palate children with midfacial skeleton dysplasia who underwent TSDO were collected retrospectively, and their corresponding 3-dimensional models were measured. Results showed no significant change in the length of the anterior or posterior cranial fossa, but the length of the middle cranial fossa increased significantly. The anterior cranial base rotated upward with the sella turcica at the center, whereas the cranial base angle increased. The sphenoid bone exhibited morphological changes. Post-TSDO, the lateral plate of the pterygoid process increased in length. The angle of the 2 lateral plates of the pterygoid process, the greater wings of the sphenoid bone, and the smaller wings of the sphenoid bone decreased. Posterior inclination of the pterygoid process increased. Mean volume of the sphenoidal sinus increased postoperatively compared with the preoperative volume. Apparent changes in the cranial base after TSDO are primarily in the middle cranial fossa, manifesting as an increase in the sphenoid bone body length, expansion of the sphenoidal sinus volume, growth of the pterygoid process forward and downward, a decrease in the angle of both the greater and smaller wings of the sphenoid bone, and an increase in the posterior inclination of the pterygoid process.

Comparison of three-dimensional maxillary growth across spheno-occipital synchondrosis maturation stages

BACKGROUND

This study aimed to three-dimensionally compare the maxillary growth among the spheno-occipital synchondrosis (SOS) maturation stages in both genders.

METHODS

This is a cross-sectional study of a retrospective type in which cone-beam computed tomography (CBCT) images of 500 patients aged 6 to 25 years (226 males and 274 females) were analyzed. The SOS was evaluated using the four-stage scoring system; completely open, partially fused, semi-fused, or completely fused. The SOS scoring and three-dimensional cephalometric measurements were analyzed by Invivo 6.0.3 software. Descriptive and analytical statistics were performed and a P-value < 0.05 was considered statistically significant.

RESULTS

There was a statistically significant difference in maxillary measurements among SOS maturation stages in both genders (P < 0.05). The mean differences in the maxillary growth among the SOS maturation stages between SOS stages 2 and 3 were higher than those between stages 1and 2 and stages 3 and 4 for maxillary length and height in both genders. However, the mean difference in the maxillary width was higher between SOS stages 1 and 2 than those stages 2 and 3 and stages 3 and 4. On other hand, there may be lesser maxillary growth between SOS stages 3 and 4 for maxillary width, length (in males), and height. The growth curves showed high active growth of the maxilla as the SOS was still fusing (especially stage 2 and 3) than those of the fused (stage 4). Moreover, the acceleration of growth occurred earlier in females than males regarding chronological age but not for SOS maturation stages.

CONCLUSIONS

The SOS maturation stages are valid and reliable maxillary skeletal maturation indicators for three-dimensional maxillary growth in both genders.

Prevalence of Chiari malformation type 1 is increased in pseudohypoparathyroidism type 1A and associated with aberrant bone development

BACKGROUND

Albright hereditary osteodystrophy (AHO) is caused by heterozygous inactivating mutations in GNAS. Patients with maternally-inherited mutations develop pseudohypoparathyroidism type 1A (PHP1A) with multi-hormone resistance and aberrant craniofacial and skeletal development among other abnormalities. Chiari malformation type 1 (CM1), a condition in which brain tissue extends into the spinal canal when the skull is too small, has been reported in isolated cases of PHP1A. It has been hypothesized to be associated with growth hormone (GH) deficiency. Given the adverse clinical sequelae that can occur if CM1 goes unrecognized, we investigated the previously undetermined prevalence of CM1, as well as any potential correlations with GH status, given the known increased prevalence of GH deficiency in PHP1A. We also investigated these metrics for low lying cerebellar tonsils (LLCT), defined as tonsillar descent less than 5 mm below the foramen magnum. In addition, we investigated possible correlations of CM1/LLCT with advanced hand/wrist bone ages and craniofacial abnormalities known to occur in PHP1A to determine whether premature chondrocyte differentiation and/or aberrant craniofacial development could be potential etiologies of CM1/LLCT through both human studies and investigations of our AHO mouse model.

METHODS

We examined patients with PHP1A in our clinic and noticed CM1 more frequently than expected. Therefore, we set out to determine the true prevalence of CM1 and LLCT in a cohort of 54 mutation-confirmed PHP1A participants who had clinically-indicated brain imaging. We examined potential correlations with GH status, clinical features, biological sex, genotype, and hand/wrist bone age determinations. In addition, we investigated the craniofacial development in our mouse model of AHO (Gnas E1+/-m) by histologic analyses, dynamic histomorphometry, and micro-computerized tomographic imaging (MCT) in order to determine potential etiologies of CM1/LLCT in PHP1A.

RESULTS

In our cohort of PHP1A, the prevalence of CM1 is 10.8%, which is at least 10-fold higher than in the general population. If LLCT is included, the prevalence increases to 21.7%. We found no correlation with GH status, biological sex, genotype, or hand/wrist bone age. Through investigations of our Gnas E1+/-m mice, the correlate to PHP1A, we identified a smaller cranial vault and increased cranial dome angle with evidence of hyperostosis due to increased osteogenesis. We also demonstrated that there was premature closure of the spheno-occipital synchondrosis (SOS), a cartilaginous structure essential to the development of the cranial base. These findings lead to craniofacial abnormalities and could contribute to CM1 and LLCT development in PHP1A.

CONCLUSION

The prevalence of CM1 is at least 10-fold higher in PHP1A compared to the general population and 20-fold higher when including LLCT. This is independent of the GH deficiency that is found in approximately two-thirds of patients with PHP1A. In light of potential serious consequences of CM1, clinicians should have a low threshold for brain imaging. Investigations of our AHO mouse model revealed aberrant cranial formation including a smaller cranium, increased cranial dome angle, hyperostosis, and premature SOS closure rates, providing a potential etiology for the increased prevalence of CM1 and LLCT in PHP1A.

Comparison of spheno-occipital synchondrosis maturation stages with three-dimensional assessment of mandibular growth

BACKGROUND

This study aimed to compare spheno-occipital synchondrosis (SOS) maturation stages with a three-dimensional assessment of mandibular growth.

METHODS

This is a cross-sectional study of a retrospective type, in which cone-beam computed tomography (CBCT) images of 500 patients aged 6 to 25 years (226 males and 274 females) were analyzed. The SOS was evaluated using the four-stage scoring system; completely open, partially fused, semi-fused, or completely fused. The SOS scoring and three-dimensional cephalometric measurements were analyzed by Invivo 6.0.3 software. Descriptive and analytical statistics were performed, and a P-value < 0.05 was considered statistically significant.

RESULTS

There was a statistically significant difference in mandibular measurements among SOS maturation stages in both sexes (P < 0.05). The skeletal growth increments of mandibular variables across the SOS stages had higher mean differences between SOS stages 2 and 3 than those between stages 1 and 2 and stages 3 and 4 in both sexes. The mandibular growth curves increased with chronological age (earlier in females) and SOS maturation stages (mostly in stages 1, 2, and 3 than stage 4).

CONCLUSIONS

The SOS maturation stages are valid and reliable mandibular skeletal indicators as evaluated with three-dimensional cephalometric mandibular measurements. The findings of growth increments and constructed growth curves of mandibular growth might be helpful in diagnosis and treatment planning.

The 27 Facial Sutures: Timing and Clinical Consequences of Closure

SUMMARY

Facial sutures contribute significantly to postnatal facial development, but their potential role in craniofacial disease is understudied. Since interest in their development and physiology peaked in the mid-twentieth century, facial sutures have not garnered nearly the same clinical research interest as calvarial sutures or cranial base endochondral articulations. In addition to reinforcing the complex structure of the facial skeleton, facial sutures absorb mechanical stress and generally remain patent into and beyond adolescence, as they mediate growth and refine the shape of facial bones. However, premature closure of these sites of postnatal osteogenesis leads to disrupted growth vectors and consequent dysmorphologies. Although abnormality in individual sutures results in isolated facial deformities, we posit that generalized abnormality across multiple sutures may be involved in complex craniofacial conditions such as syndromic craniosynostosis. In this work, the authors comprehensively review 27 key facial sutures, including physiologic maturation and closure, contributions to postnatal facial development, and clinical consequences of premature closure.

When does the spheno-occipital synchondrosis close?

In forensic work, the spheno-occipital synchondrosis helps identify the deceased as a child or young adult. In the past, it was generally held that the synchondrosis closed between the late teens and 25 years, but recent studies have suggested closure in adolescence. There are also suggestions that the age at closure recorded might be influenced by ancestry and the technique used to study the joint. This comprehensive review of the literature of the past 60 years concludes that the age of closure of the spheno-occipital synchondrosis is very variable, from childhood to the mid-twenties, with no obvious association with the geographical location of the study population. We note that some studies on bony specimens indicated later closure than others using clinical images and draw attention to a possible misinterpretation of the so-called "fusion scar" which might explain this incongruity. Despite an increasing acceptance that the synchondrosis usually closes in adolescence, we are concerned that insufficient heed is being paid to reports of closure in childhood and in the early to mid-twenties. We conclude that, for forensic purposes, it is unwise to declare that the synchondrosis closes in adolescence. It would be safer to state that a closed synchondrosis indicates a person 6 years or over and that an open synchondrosis may be seen up to the mid-twenties. Clearly, for younger individuals, the dentition and, for all individuals in this age range, documentation of unfused postcranial epiphyses would be important in attempting to narrow this very broad estimation of age.

Morphology of the Occipital Bones and Foramen Magnum Resulting From Premature Minor Suture Fusion in Crouzon Syndrome

To identify skull-base growth patterns in Crouzon syndrome, we hypothesized premature minor suture fusion restricts occipital bone development, secondarily limiting foramen magnum expansion.

Skull-base suture closure degree and cephalometric measurements were retrospectively studied using preoperative computed tomography (CT) scans and multiple linear regression analysis.

Evaluation of multi-institutional CT images and 3D reconstructions from Wake Forest's Craniofacial Imaging Database (WFCID).

Sixty preoperative patients with Crouzon syndrome under 12 years-old were selected from WFCID. The control group included 60 age- and sex-matched patients without craniosynostosis or prior craniofacial surgery.

None.

2D and 3D cephalometric measurements.

3D volumetric evaluation of the basioccipital, exo-occipital, and supraoccipital bones revealed decreased growth in Crouzon syndrome, attributed solely to premature minor suture fusion. Spheno-occipital (β = -398.75; P < .05) and petrous-occipital (β = -727.5; P < .001) suture fusion reduced growth of the basioccipital bone; lambdoid suture (β = -14 723.1; P < .001) and occipitomastoid synchondrosis (β = -16 419.3; P < .001) fusion reduced growth of the supraoccipital bone; and petrous-occipital suture (β = -673.3; P < .001), anterior intraoccipital synchondrosis (β = -368.47; P < .05), and posterior intraoccipital synchondrosis (β = -6261.42; P < .01) fusion reduced growth of the exo-occipital bone. Foramen magnum morphology is restricted in Crouzon syndrome but not directly caused by early suture fusion.

Premature minor suture fusion restricts the volume of developing occipital bones providing a plausible mechanism for observed foramen magnum anomalies.

Physiologic Timeline of Cranial-Base Suture and Synchondrosis Closure

BACKGROUND

Fusion of cranial-base sutures/synchondroses presents a clinical conundrum, given their often unclear "normal" timing of closure. This study investigates the physiologic fusion timelines of cranial-base sutures/synchondroses.

METHODS

Twenty-three age intervals were analyzed in subjects aged 0 to 18 years. For each age interval, 10 head computed tomographic scans of healthy subjects were assessed. Thirteen cranial-base sutures/synchondroses were evaluated for patency. Partial closure in greater than or equal to 50 percent of subjects and complete bilateral closure in less than 50 percent of subjects defined the fusion "midpoint." Factor analysis identified clusters of related fusion patterns.

RESULTS

Two hundred thirty scans met inclusion criteria. The sutures' fusion midpoints and completion ages, respectively, were as follows: frontoethmoidal, 0 to 2 months and 4 years; frontosphenoidal, 6 to 8 months and 12 years; and sphenoparietal, 6 to 8 months and 4 years. Sphenosquamosal, sphenopetrosal, parietosquamosal, and parietomastoid sutures reached the midpoint at 6 to 8 months, 8 years, 9 to 11 months, and 12 years, respectively, but rarely completed fusion. The occipitomastoid suture partially closed in less than or equal to 30 percent of subjects. The synchondroses' fusion midpoints and completion ages, respectively, were as follows: sphenoethmoidal, 3 to 5 months and 5 years; spheno-occipital, 9 years and 17 years; anterior intraoccipital, 4 years and 10 years; and posterior intraoccipital, 18 to 23 months and 4 years. The petro-occipital synchondrosis reached the midpoint at 11 years and completely fused in less than 50 percent of subjects. Order of fusion of the sutures, but not the synchondroses, followed the anterior-to-posterior direction. Factor analysis suggested three separate fusion patterns.

CONCLUSIONS

The fusion timelines of cranial-base sutures/synchondroses may help providers interpret computed tomographic data of patients with head-shape abnormalities. Future work should elucidate the mechanisms and sequelae of cranial-base suture fusion that deviates from normal timelines.

Facial Suture Pathology in Syndromic Craniosynostosis: Human and Animal Studies

BACKGROUND

Facial deformities in syndromic craniosynostosis are not only functionally, psychosocially, and aesthetically impairing but also notoriously challenging to reconstruct. Whether facial suture synostosis plays a significant role in the pathogenesis of these deformities is inadequately studied in human patients.

METHODS

The MEDLINE database was queried using a methodologically generated search term inventory. Article inclusion was adjudicated by 2 authors after independent review. Articles provided insight into facial suture involvement in either syndromic craniosynostosis patients or animal models of disease.

RESULTS

Comprehensive review yielded 19 relevant articles meeting inclusion criteria. Mid-20th century craniofacial biologists characterized how patent facial sutures are essential for normal postnatal facial development. They also posited that premature ossification disrupts growth vectors, causing significant dysmorphologies. Recently, facial suture synostosis was found to cause midfacial deformities independent of cranial base pathology in mouse models of syndromic craniosynostosis. Few recent studies have begun exploring facial suture involvement in patients, and although they have paved the way for future research, they bear significant limitations.

CONCLUSIONS

The hypothesis that facial suture synostosis acts in conjunction with cranial base pathology to produce the prominent, multifocal facial deformities in syndromic craniosynostosis may fundamentally alter surgical management and warrants further investigation. Methodically evaluating the literature, this review synthesizes all basic science and human clinical research thus far on the role of facial sutures in syndromic craniosynostosis and elucidates important topics for future research. We ultimately identify the need for rigorous imaging studies that longitudinally evaluate facial osteology across patients with various craniosynostosis syndromes.

Effect of Early Spheno-Occipital Synchondrosis Fusion in Preadolescent Patients With Syndromic Craniosynostosis on Craniofacial Skeletal Patterns: A Preliminary Study Using Cephalometric Analysis

ABSTRACT

The purpose of this study was to investigate the effects of early spheno-occipital synchondrosis (SOS) fusion in preadolescent patients with syndromic craniosynostosis (SC) on the craniofacial skeletal patterns. Twenty preadolescent SC patients were divided into the fused SOS (FS, n = 10; 8 Crouzon and 2 Apert) and not-fused SOS groups (NFS, n = 10; 9 Crouzon and 1 Apert). Lateral cephalograms (mean age: 9.60 years, cervical vertebral maturation index: stage I and II) were used to investigate the skeletal sagittal (ANB) and vertical patterns (SN-GoMe), upward inclination of the anterior cranial base (ACB; SN-FH), degree of midface hypoplasia (MH, SNA), retrusive position of orbitale (SNO), and forward position of the condyle in relation to sella (saddle angle). Using the ordinal values calculated by ethnic norm (criteria: moderate, over ±1 standard deviation, severe, over ±2 standard deviation), statistical analysis was performed. The FS group showed a higher percentage of severe MH than the NFS group (70% versus 10%, P < 0.05). Although the 2 groups did not differ in the distribution of ANB, SN-GoMe, saddle angle, and SN-FH (all P > 0.05), the FS group showed relatively higher percentages of severe Class III (100% versus 70%), severe hyper-divergent pattern (40% versus 10%), severely forward condyle position (30% versus 0%), and moderate and severe upward anterior cranial base inclination (90% versus 50%) than the NFS group. However, the 2 groups exhibited the same distribution of moderately and severely retrusive orbitale position ([50%, 20%], P > 0.05). Early SOS fusion in preadolescent SC patients might not be related to retrusive orbitale position, but to severe MH.

Respective Roles of Craniosynostosis and Syndromic Influences on Cranial Fossa Development

BACKGROUND

Little is known about the detailed growth of the cranial fossae, even though they provide an important structural connection between the cranial vault and the facial skeleton. This study details the morphologic development of isolated cranial vault synostosis and associated syndromes on cranial fossa development.

METHODS

A total of 125 computed tomographic scans were included (nonsyndromic bicoronal synostosis, n = 36; Apert syndrome associated with bicoronal synostosis, n = 24; Crouzon syndrome associated with bicoronal synostosis, n = 11; and controls, n = 54). Three-dimensional analyses were produced using Materialise software.

RESULTS

The regional anterior and middle cranial fossae volumes of nonsyndromic bicoronal synostosis are characterized by significant increases of 43 percent (p < 0.001) and 60 percent (p < 0.001), respectively, and normal posterior cranial fossa volume. The cranial fossae depths of nonsyndromic bicoronal synostosis were increased, by 37, 42, and 21 percent (all p < 0.001) for anterior, middle, and posterior cranial fossae, respectively, accompanying the shortened cranial fossae lengths. The volume and morphology of all cranial fossae in Apert syndrome nearly paralleled nonsyndromic bicoronal synostosis. However, Crouzon syndrome had reduced depths of cranial fossae, and more restricted fossa volumes than both Apert syndrome and nonsyndromic bicoronal synostosis.

CONCLUSIONS

Cranial vault suture synostosis is likely to be more influential on cranial fossae development than other associated influences (genetic, morphologic) in Apert and Crouzon syndromes. Isolated Apert syndrome pathogenesis is associated with an elongation of the anterior cranial fossa length in infants, whereas in Crouzon syndrome, there is a tendency to reduce cranial fossa depth, suggesting individual adaptability in cranial fossae development related to vault synostosis.

Craniofacial, oral, and cervical morphological characteristics in Japanese patients with Apert syndrome or Crouzon syndrome

BACKGROUND AND OBJECTIVES

Mutations in the fibroblast growth factor receptor 2 (FGFR2) gene are responsible for both Apert syndrome (AS) and Crouzon syndrome (CS). These diseases share phenotypic characteristics, including midfacial hypoplasia and premature fusion of the calvarial suture(s). Given the extensive range of craniofacial growth and developmental abnormalities, management of these patients requires a multidisciplinary approach. This study aimed to compare craniofacial, oral, and cervical morphological characteristics in Japanese orthodontic patients with AS or CS.

SUBJECTS AND METHODS

Lateral cephalograms, orthopantomograms, dental casts, medical interview records, facial photographs, and intraoral photographs of 7 AS patients and 12 CS patients on initial visits were used in this study. Cephalometric analyses were performed, and standard scores were calculated based on age- and sex-matched Japanese standard values.

RESULTS

Cephalometric analysis revealed that AS patients had significantly more severe maxillary hypoplasia in two dimensions and increased clockwise mandibular rotation. Additionally, cleft of the soft palate, anterior open bite, severe crowding in the maxillary dental arch, and congenitally missing teeth occurred more frequently among AS patients. Multiple fusions between cervical vertebrae C2, C3, C5, and C6 were observed in the AS patients.

LIMITATIONS

Small sample size.

CONCLUSIONS/IMPLICATIONS

Our study shows that AS patients have more severe craniofacial and maxillofacial deformities than CS patients.

Defining the critical period of hedgehog pathway inhibitor-induced cranial base dysplasia in mice

BACKGROUND

The hedgehog signaling pathway is critical for developmental patterning of the limb, craniofacial and axial skeleton. Disruption of this pathway in mice leads to a series of structural malformations, but the exact role and critical period of the Hh pathway in the early development of the cranial base have been rarely described.

RESULTS

Embryos exposed to vismodegib from E7.5, E9.5, and E10.5 had a higher percentage of cranial base fenestra. The peak incidence of hypoplasia in sphenoid winglets and severe craniosynostosis in cranial base synchondroses was observed when vismodegib was administered between E9.5 and E10.5. Cranial base craniosynostosis results from accelerating terminal differentiation of chondrocytes and premature osteogenesis.

CONCLUSIONS

We define the critical periods for the induction of cranial base deformity by vismodegib administration at a meticulous temporal resolution. Our findings suggest that the Hh pathway may play a vital role in the early development of the cranial base. This research also establishes a novel and easy-to-establish mouse model of synostosis in the cranial base using a commercially available pathway-selective inhibitor.

Fusion patterns of the spheno-occipital synchondrosis in the age range of 9-22: A computed tomography analysis

OBJECTIVES

To assess the fusion patterns of the spheno-occipital synchondrosis (SOS) in the age range of 9-22 using CT and CBCT images of an Iranian population.

SETTING/SAMPLE POPULATION

Spiral CT and CBCT scans of 763 subjects (459 males and 304 females) aged 9-22 were evaluated. The scans had to cover the cranial base area, and those with diseases affecting the bone density, cranial base masses and history of trauma were excluded.

MATERIALS AND METHODS

Two oral and maxillofacial radiologists scored the images with regard to the status of SOS fusion based on a 5-stage system. Mann-Whitney, Kruskal-Wallis and Fisher's exact tests were used for data analysis. Age and SOS fusion stages were evaluated through Spearman correlation and linear regression methods (α = 0.01).

RESULTS

The earliest age for onset of SOS fusion was 9 in both sexes. Open SOS could be observed until the age of 15 and 14 in males and females, respectively. The earliest age of complete fusion was 12 in males and 13 in females. Furthermore, there was a significant, positive correlation between age and the different stages of SOS fusion (P < .001).

CONCLUSION

A significant correlation exists between age and the fusion stages of SOS, rendering it an appropriate means of age estimation during growth periods. Fusion of SOS begins approximately 2 years earlier in females; however, it ends at the age of 17 in both sexes. The fusion scar can be detected up to the age of 12 and 13 in males and females, respectively.

Timing of Spheno-Occipital Synchondrosis Ossification in Children and Adolescents with Cleft Lip and Palate: A Retrospective Case-Control Study

Background: Cleft lip and palate (CLP) can affect the development of the maxilla; which may create a midfacial deficiency as well as an interference of the facial growth pattern and dentofacial esthetics. Objective: This study aimed to estimate the chronological age of complete fusion of the spheno-occipital synchondrosis (SOS) in cleft lip and palate patients and a control group; using cone beam computed tomography (CBCT) images. Methods: In this retrospective study; 125 patients were enrolled (cleft lip and palate group (n = 91); control group (n = 34)). Age comparison was made with a chi-square test; and a Kaplan–Meier analysis determined the median time to reach complete fusion of the spheno-occipital synchondrosis (p < 0.05). Results: The experimental group showed statistically significant differences in the median time for complete ossification between males and females (p = 0.019). The median time for complete ossification of the spheno-occipital synchondrosis was; for males; 15.0 years in both groups; for females; it was 14.0 years and 13.0 years in the experimental group and in the control group; respectively. Both for males and females; there were no statistically significant differences between experimental and control groups (p = 0.104). Conclusions: The present study showed no differences in the ossification of the spheno-occipital synchondrosis between individuals with and without cleft lip and/or palate.

New Insights Into Cranial Synchondrosis Development: A Mini Review

The synchondroses formed via endochondral ossification in the cranial base are an important growth center for the neurocranium. Abnormalities in the synchondroses affect cranial base elongation and the development of adjacent regions, including the craniofacial bones. In the central region of the cranial base, there are two synchondroses present—the intersphenoid synchondrosis and the spheno-occipital synchondrosis. These synchondroses consist of mirror image bipolar growth plates. The cross-talk of several signaling pathways, including the parathyroid hormone-like hormone (PTHLH)/parathyroid hormone-related protein (PTHrP), Indian hedgehog (Ihh), Wnt/β-catenin, and fibroblast growth factor (FGF) pathways, as well as regulation by cilium assembly and the transcription factors encoded by the RUNX2, SIX1, SIX2, SIX4, and TBX1 genes, play critical roles in synchondrosis development. Deletions or activation of these gene products in mice causes the abnormal ossification of cranial synchondrosis and skeletal elements. Gene disruption leads to both similar and markedly different abnormalities in the development of intersphenoid synchondrosis and spheno-occipital synchondrosis, as well as in the phenotypes of synchondroses and skeletal bones. This paper reviews the development of cranial synchondroses, along with its regulation by the signaling pathways and transcription factors, highlighting the differences between intersphenoid synchondrosis and spheno-occipital synchondrosis.

TBX1 Regulates Chondrocyte Maturation in the Spheno-occipital Synchondrosis

The synchondrosis in the cranial base is an important growth center for the craniofacial region. Abnormalities in the synchondroses affect the development of adjacent regions, including the craniofacial skeleton. Here, we report that the transcription factor TBX1, the candidate gene for DiGeorge syndrome, is expressed in mesoderm-derived chondrocytes and plays an essential and specific role in spheno-occipital synchondrosis development by inhibiting the expression of genes involved in chondrocyte hypertrophy and osteogenesis. In Tbx1-deficient mice, the spheno-occipital synchondrosis was completely mineralized at birth. TBX1 interacts with RUNX2, a master molecule of osteoblastogenesis and a regulator of chondrocyte maturation, and suppresses its transcriptional activity. Indeed, deleting Tbx1 triggers accelerated mineralization due to accelerated chondrocyte differentiation, which is associated with ectopic expression of downstream targets of RUNX2 in the spheno-occipital synchondrosis. These findings reveal that TBX1 acts as a regulator of chondrocyte maturation and osteogenesis during the spheno-occipital synchondrosis development. Thus, the tight regulation of endochondral ossification by TBX1 is crucial for the normal progression of chondrocyte differentiation in the spheno-occipital synchondrosis.

Vestiges of Ossified Spheno-occipital Suture in an Elderly Patient With Down Syndrome and Lateral Skull Base Fracture

BACKGROUND/AIM

Down syndrome (DS) patients often show characteristic changes in the skull, e.g. short cranial base. The synchondroses of the skull base have a significant influence on the shape of the skull. The sphenooccipital synchondrosis (SOS) is the last of the basal synchondroses to ossify. This report is about residual ossification of SOS in an elderly patient with DS.

CASE REPORT

The 65-year-old DS patient was polytraumatized by a fall. In the course of treatment, a purulent otitis externa on the right side was diagnosed, which had developed as a result of the fracture of the fossa glenoidalis. Computed tomograms of the skull base showed the fracture of the mandibular condyle, glenoid fossa and vestiges of SOS.

CONCLUSION

The coincidental finding of vestiges of SOS in an elderly patient with DS raises the question of whether cross-sectional skull base images can show differences in the ossification of SOS between DS patients and a normal population.

Role of thyroid hormones in craniofacial development

The development of the craniofacial skeleton relies on complex temporospatial organization of diverse cell types by key signalling molecules. Even minor disruptions to these processes can result in deleterious consequences for the structure and function of the skull. Thyroid hormone deficiency causes delayed craniofacial and tooth development, dysplastic facial features and delayed development of the ossicles in the middle ear. Thyroid hormone excess, by contrast, accelerates development of the skull and, in severe cases, might lead to craniosynostosis with neurological sequelae and facial hypoplasia. The pathogenesis of these important abnormalities remains poorly understood and underinvestigated. The orchestration of craniofacial development and regulation of suture and synchondrosis growth is dependent on several critical signalling pathways. The underlying mechanisms by which these key pathways regulate craniofacial growth and maturation are largely unclear, but studies of single-gene disorders resulting in craniofacial malformations have identified a number of critical signalling molecules and receptors. The craniofacial consequences resulting from gain-of-function and loss-of-function mutations affecting insulin-like growth factor 1, fibroblast growth factor receptor and WNT signalling are similar to the effects of altered thyroid status and mutations affecting thyroid hormone action, suggesting that these critical pathways interact in the regulation of craniofacial development.

The growth of the posterior cranial fossa in FGFR2-induced faciocraniosynostosis: A review

BACKGROUND

The growth of the posterior fossa in syndromic craniostenosis was studied in many papers. However, few studies described the pathophysiological growth mechanisms in non-operated infants with fibroblast growth factor receptor (FGFR) type 2 mutation (Crouzon, Apert or Pfeiffer syndrome), although these are essential to understanding cranial vault expansion and hydrocephalus treatment in these syndromes.

OBJECTIVE

A review of the medical literature was performed, to understand the physiological and pathological growth mechanisms of the posterior fossa in normal infants and infants with craniostenosis related to FGFR2 mutation.

DISCUSSION

Of the various techniques for measuring posterior fossa volume, direct slice-by-slice contouring is the most precise and sensitive. Posterior fossa growth follows a bi-phasic pattern due to opening of the petro-occipital, occipitomastoidal and spheno-occipital sutures. Some studies reported smaller posterior fossae in syndromic craniostenosis, whereas direct contouring studies reported no difference between normal and craniostenotic patients. In Crouzon syndrome, synchondrosis fusion occurs earlier than in normal subjects, and follows a precise pattern. This premature fusion in Crouzon syndrome leads to a stenotic foramen magnum and facial retrusion.

Imaging study of midface growth with bone-borne trans-sutural distraction osteogenesis therapy in growing cleft lip and palate patients

Trans-sutural distraction osteogenesis (TSDO) promotes midface growth in growing cleft lip and palate (CLP) patients with midfacial hypoplasia. The superficial skeletal changes after therapy revealed rotation advancement of the midfacial skeleton associated with differential displacement in each segment, but reports rarely focus on the changes of internal structures, including circummaxillary sutures, the maxillary tuberosity and the maxillary sinus, which may play a crucial role during this process. This study evaluated the computed tomographic (CT) images of 26 growing CLP patients who received bone-borne TSDO therapy. The results revealed that the most prominent new bone formation occurred in the pterygomaxillary suture and pushed the P-point forward. The maxillary first molar exhibited significantly greater advancement compared with the P-point due to the growth of the maxillary tuberosity. The contribution ratio values of the advancement of the maxillary tuberosity and P-point to the maxillary first molar were 26% and 74%, respectively, in UCLP and 25% and 75%, respectively, in BCLP. Furthermore, the maxillary sinus volume was also significantly increased. In conclusion, midface growth with bone-borne TSDO therapy depends on both secondary displacement promoted by sutural bone formation mainly in the pterygomaxillary suture and primary displacement by growth of the maxillary tuberosity and maxillary sinus volume.

Mouse models for the study of cranial base growth and anomalies

The cranial base is a central and integral component of the cranioskeleton, yet little is known about its growth. Despite the dissimilarities between human and murine cranioskeletal form, mouse models are proving instrumental in studying craniofacial growth. The objectives of this review are to summarize recent findings from numerous mouse models that display growth defects in one or more cranial base synchondroses, with accompanying changes in chondrocyte cellular zones. Many of these models also display altered growth of the cranial vault and/or the facial region. FGFR, PTHrP, Ihh, BMP and Wnt/β-catenin, as well as components of primary cilia, are the major genes and signalling pathways identified in cranial base synchondroses. Together, these models are helping to uncover specific genetic influences and signalling pathways operational at the cranial base synchondroses. Many of these genes are in common with those of importance in the cranial vault and the facial skeleton, emphasizing the molecular integration of growth between the cranial base and other cranial regions. Selected models are also being utilized in testing therapeutic agents to correct defective craniofacial and cranial base growth.

Midface Distraction Osteogenesis Using a Modified External Device With Elastic Distraction for Crouzon Syndrome

PURPOSE

Midface distraction osteogenesis has been popularized for the correction of midface hypoplasia associated with exophthalmos and obstructive sleep apnea in patients with Crouzon syndrome. The purpose of this study was to present the method of utilizing the modified external device with elastic distraction for the midface advancement in Crouzon syndrome, and the clinical outcomes and skeletal changes were analyzed.

METHODS

Five consecutive patients with Crouzon syndrome underwent Le Fort III osteotomy with midface advancement using a modified external device with elastic distraction. The distraction system consists of a rigid external distractor, nickel-titanium shape memory alloy spring, and bone-borne traction hooks. The midface advancement was initiated with the bony anchorage around the nasomaxillary buttress at the level between occlusal plane and infraorbital margin. The device was activated at a rate of 1 to 1.5 mm per day by the length of spring. The skeletal changes were analyzed by cephalometric and computed tomographic measurement.

RESULTS

All the patients achieved improvements in midface appearance, obstructive sleep apnea, exophthalmos, and occlusion. No complications occurred during this procedure. After the distraction, 1 patient developed an open bite that was corrected by a definitive orthognathic surgery. Cephalometric and computed tomographic measurement analysis showed a differential advancement of midface with more at the occlusal level than the orbital level. In addition, midface suture and bone remodeling was also observed in growing patient.

CONCLUSIONS

Our modified external device with elastic distraction offers an alternative method to achieve midface advancement in patients with Crouzon syndrome.

Role of Matrix Gla protein in midface development: Recent advances

Craniofacial development is a delicate process that involves complex interactions among cells of multiple developmental origins, their migration, proliferation, and differentiation. Tissue morphogenesis of the craniofacial skeleton depends on genetic and environmental factors, and on specific signaling pathways, which are still not well understood. Developmental defects of the midface caused by the absence, delays, or premature fusion of nasal and maxillary prominences vary in severity; leading to clefts, hypoplasias, and midline expansion. In the current review, we focus on the importance of the chondrocranium in craniofacial growth and how its impaired development leads to midface hypoplasia. More importantly, we reported how Matrix Gla protein (MGP), a potent inhibitor of extracellular matrix mineralization, facilitates midface development by preventing ectopic calcification of the nasal septum. In fact, MGP may act as a common link in multiple developmental pathologies all showing midface hypoplasia caused by abnormal cartilage calcification. This brief review discusses the gap in knowledge in the field, raises pertinent questions, which remain unanswered, and sheds light on the future research directions.

The Significance of Squamosal Suture Synostosis

The squamosal suture is one of the lateral minor skull sutures, separating the parietal and squamous temporal bones. While the phenotypic appearances and sequelae of synostosis of the major cranial vault sutures are well documented, little is reported concerning synostosis of the squamosal suture (SQS). The aim of this study was to determine the frequency of squamosal suture synostosis, and to document the significance of this entity.A retrospective review of the diagnostic imaging for all new pediatric patients (aged ≤16 years) referred to the Oxford Craniofacial Unit between January 2008 and February 2013 was completed to identify patients with SQS. Computed tomography (CT) imaging was available in 422 patients and the axial and three-dimensional reconstructed images reviewed.Squamosal suture synostosis was confirmed in 38 patients (9%). It was present in conjunction with major suture synostosis in 33 patients and in isolation in 5. The incidence increased with age. It was more common in patients with syndromic craniosynostosis (18%) and associated syndromic conditions (36%) than in those with isolated major suture synostosis (6%). It was found to occur with coronal, lambdoid, and sagittal synostosis, but was most frequent with multisuture fusion patterns. Squamosal suture synostosis was not associated with a consistent calvarial deformity either in isolation or when associated with a major suture fusion. No patient underwent surgery specifically to correct SQS.In conclusion, contrary to previous reports, squamosal suture synostosis is a relatively frequent finding in the general case mix of a typical craniofacial unit, but is of limited clinical significance.

Postnatal Craniofacial Skeletal Development of Female C57BL/6NCrl Mice

The craniofacial skeleton is a complex and unique structure. The perturbation of its development can lead to craniofacial dysmorphology and associated morbidities. Our ability to prevent or mitigate craniofacial skeletal anomalies is at least partly dependent on our understanding of the unique physiological development of the craniofacial skeleton. Mouse models are critical tools for the study of craniofacial developmental abnormalities. However, there is a lack of detailed normative data of mouse craniofacial skeletal development in the literature. In this report, we employed high-resolution micro-computed tomography (μCT) in combination with morphometric measurements to analyze the postnatal craniofacial skeletal development from day 7 (P7) through day 390 (P390) of female C57BL/6NCrl mice, a widely used mouse strain. Our data demonstrates a unique craniofacial skeletal development pattern in female C57BL/6NCrl mice, and differentiates the early vs. late craniofacial growth patterns. Additionally, our data documents the complex and differential changes in bone parameters (thickness, bone volume, bone volume/tissue volume, bone mineral density, and tissue mineral density) of various craniofacial bones with different embryonic origins and ossification mechanisms during postnatal growth, which underscores the complexity of craniofacial bone development and provides a reference standard for future quantitative analysis of craniofacial bones.

Posterior cranial base natural growth and development: A systematic review

OBJECTIVE

To provide a synthesis of the published studies evaluating the natural growth and development of the human posterior cranial base (S-Ba).

MATERIALS AND METHODS

The search was performed on MEDLINE, Embase, PubMed, and all EBM Reviews electronic databases. In addition, reference lists of the included studies were hand-searched. Articles were included if they analyzed posterior cranial-base growth in humans specifically. Study selection, data extraction, and risk of bias assessment were completed in duplicate. A meta-analysis was not justified.

RESULTS

Finally, 23 published studies were selected: 5 cross-sectional and 18 cohort studies. Articles were published between 1955 and 2015, and all were published in English. The sample sizes varied between 20 and 397 individuals and consisted of craniofacial measurements from either living or deceased human skulls. Validity of the measurements was not determined in any of the studies, while six papers reported some form of reliability assessment. All the articles included multiple time points within the same population or data from multiple age groups. Growth of S-Ba was generally agreed to be from spheno-occipital synchondrosis growth. Basion displaced downward and backward and sella turcica moved downward and backward during craniofacial growth. Timing of cessation of S-Ba growth was not conclusive due to limited identified evidence.

CONCLUSIONS

Current evidence suggests that S-Ba is not totally stable, as its dimensions change throughout craniofacial growth and a minor dimensional change is observed even in late adulthood.

Comparison of endocranial morphology according to age in one-piece fronto-orbital advancement using a distraction in craniosynostotic plagiocephaly

The capacity for cranial remodelling is known to be better at younger ages. The timing of cranioplasty could affect the axis of the skull base. We investigated whether age at the time of distraction is related to the outcome of endocranial morphology correction. In this retrospective study, we investigated the surgical outcome of 14 patients with unilateral craniosynostotic plagiocephaly who underwent one-piece fronto-orbital advancement without bandeau by using a distraction technique between April 2005 and December 2015. Satisfactory results were achieved in all 14 patients with unilateral coronal suture craniosynostosis. An average distraction of 27.3 mm was obtained without detachment from the dura mater. The endocranial angulation of the anteroposterior axis was reduced from 165.4° to 173.5° on average, and the average total change was 8.1°. Between patients aged <1 year and those >1 year, there was a statistically significant difference in the postoperative endocranial angulation of the anteroposterior axis after 3 months (p = 0.003). The distraction techniques resulted in better correction of endocranial morphology. This indicates that the changes in the skull base axis after one-piece fronto-orbital advancement without bandeau are related to the remodelling capacity of the skull base in growing children based on the dura mater.

Matrix Gla protein deficiency impairs nasal septum growth, causing midface hypoplasia

Genetic and environmental factors may lead to abnormal growth of the orofacial skeleton, affecting the overall structure of the face. In this study, we investigated the craniofacial abnormalities in a mouse model for Keutel syndrome, a rare genetic disease caused by loss-of-function mutations in the matrix Gla protein (MGP) gene. Keutel syndrome patients show diffuse ectopic calcification of cartilaginous tissues and impaired midface development. Our comparative cephalometric analyses of micro-computed tomography images revealed a severe midface hypoplasia in Mgp-/- mice. In vivo reporter studies demonstrated that the Mgp promoter is highly active at the cranial sutures, cranial base synchondroses, and nasal septum. Interestingly, the cranial sutures of the mutant mice showed normal anatomical features. Although we observed a mild increase in mineralization of the spheno-occipital synchondrosis, it did not reduce the relative length of the cranial base in comparison with total skull length. Contrary to this, we found the nasal septum to be abnormally mineralized and shortened in Mgp-/- mice. Transgenic restoration of Mgp expression in chondrocytes fully corrected the craniofacial anomalies caused by MGP deficiency, suggesting a local role for MGP in the developing nasal septum. Although there was no up-regulation of markers for hypertrophic chondrocytes, a TUNEL assay showed a marked increase in apoptotic chondrocytes in the calcified nasal septum. Transmission electron microscopy confirmed unusual mineral deposits in the septal extracellular matrix of the mutant mice. Of note, the systemic reduction of the inorganic phosphate level was sufficient to prevent abnormal mineralization of the nasal septum in Mgp-/-;Hyp compound mutants. Our work provides evidence that modulation of local and systemic factors regulating extracellular matrix mineralization can be possible therapeutic strategies to prevent ectopic cartilage calcification and some forms of congenital craniofacial anomalies in humans.

Developmental Regulation of the Growth Plate and Cranial Synchondrosis

Long bones and the cranial base are both formed through endochondral ossification. Elongation of long bones is primarily through the growth plate, which is a cartilaginous structure at the end of long bones made up of chondrocytes. Growth plate chondrocytes are organized in columns along the longitudinal axis of bone growth. The cranial base is the growth center of the neurocranium. Synchondroses, consisting of mirror-image growth plates, are critical for cranial base elongation and development. Over the last decade, considerable progress has been made in determining the roles of the parathyroid hormone-related protein, Indian hedgehog, fibroblast growth factor, bone morphogenetic protein, and Wnt signaling pathways in various aspects of skeletal development. Furthermore, recent evidence indicates the important role of the primary cilia signaling pathway in bone elongation. Here, we review the development of the growth plate and cranial synchondrosis and the regulation by the above-mentioned signaling pathways, highlighting the similarities and differences between these 2 structures.