Cranial base in craniofacial development: developmental features, influence on facial growth, anomaly, and molecular basis

Sphenoidal-clival neoformation: an endoscopic approach

The cranial base has distinct embryologic origins. The anterior cranial base is derived solely from the neural crest, similar to other facial bones, whereas the posterior cranial base is formed by the paraxial mesoderm. Both these parts also develop and grow with distinct features. Unlike other craniofacial bones that are mostly formed through intramembraneous ossification, the cranial base is formed through endochondral ossification, in which a cartilage plate, known as the chondrocranium, is formed first and soon replaced by bones. Individual bones are then connected by cartilaginous structures, termed synchondroses, which are morphologically similar to long-bone growth plates.These processes justify the presence of a disembryogenic cyst in the sphenoid bone. The authors present a case of a clival-sphenoidal region neoformation treated with a transnasal-endoscopic approach.

Orthopedic protraction of the maxilla may affect cranial base synchondroses indicated by increased expressions of growth factors

OBJECTIVES

To examine the biological adaptation of cranial base synchondroses (CBS) when the maxilla was forward positioned by orthopedic force.

SETTING AND SAMPLE POPULATION

The Department of Orthodontics at Shanghai Jiao Tong University. 50 Sprague-Dawley rats, 4 weeks of age, were divided into experimental (n=30) and control groups (n=20).

MATERIAL AND METHODS

An orthopedic appliance was fitted to the cranio-maxillary complex to advance the maxilla forward. The animals in the experimental group, together with the counterparts in the control group, were sacrificed at days 1, 3, 5, 7, and 14, respectively. The whole cranial base housing both the spheno-ethmoid (SES) and spheno-occipital synchondroses (SOS) was removed for tissue processing and immunotest of Sox9, Core-binding factor α 1 (Cbfa1), and vascular endothelial growth factor (VEGF), three carefully selected growth factors that are markers of chondrogenesis in different stages and its transition to endochondral ossification. Semiquantitative analysis was also conducted by using a computerizing imaging system.

RESULTS

The temporal tendency of the changes in the expressions of the three growth factors featured an increase from Day 3 and onwards for Cbfa1 and VEGF, and a following decline after Day 5 for Sox9. In both SES and SOS, the expressions of the three growth factors were significantly stronger in the experimental groups than that in groups (p<0.05).

CONCLUSIONS

Protractive orthopedic force imposed on the maxilla provokes an enhancement of chondrogenic process in CBS.

Retinoic acid modulates chondrogenesis in the developing mouse cranial base

The retinoic acid (RA) signaling pathway is known to play important roles during craniofacial development and skeletogenesis. However, the specific mechanism involving RA in cranial base development has not yet been clearly described. This study investigated how RA modulates endochondral bone development of the cranial base by monitoring the RA receptor RARγ, BMP4, and markers of proliferation, programmed cell death, chondrogenesis, and osteogenesis. We first examined the dynamic morphological and molecular changes in the sphenooccipital synchondrosis-forming region in the mouse embryo cranial bases at E12-E16. In vitro organ cultures employing beads soaked in RA and retinoid-signaling inhibitor citral were compared. In the RA study, the sphenooccipital synchondrosis showed reduced cartilage matrix and lower BMP4 expression while hypertrophic chondrocytes were replaced with proliferating chondrocytes. Retardation of chondrocyte hypertrophy was exhibited in citral-treated specimens, while BMP4 expression was slightly increased and programmed cell death was induced within the sphenooccipital synchondrosis. Our results demonstrate that RA modulates chondrocytes to proliferate, differentiate, or undergo programmed cell death during endochondral bone formation in the developing cranial base.

Short mandible, maxilla and cranial base are common in patients with neurofibromatosis 1

Neurofibromatosis type 1 (NF1) is an autosomal-dominant neuro-cutaneous-skeletal syndrome. Neurofibromatosis type 1 is one of the Rasopathies, and at the cellular level NF1 results in a hyperactive Ras pathway. In the current investigation, our aim was to study lateral skull X-rays (cephalograms) to assess NF1-related craniofacial morphology. A total of 85 Finnish patients with NF1, including four patients with plexiform neurofibroma of the 5th cranial nerve, and their age- and gender-matched controls, were enrolled in the study. The results showed that patients with NF1 typically had a short mandible, maxilla, and cranial base compared with healthy controls, irrespective of age, but the results were statistically significant only in adults. The length of the mandible, the maxilla and the cranial base correlated with the height of patients under 19 yr of age, but this correlation was absent in adult patients. Thus, a tall adult patient with NF1 may have short jaws and a short cranial base. In conclusion, the NF1 gene apparently influences the growth of craniofacial bones, thus contributing to the craniofacial morphology in NF1.

3-Dimensional cone-beam computed tomography analysis of transverse changes with Schwarz appliances on both jaws

OBJECTIVE

To evaluate transverse changes from Schwarz appliances on both jaws in young, growing patients using cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

All subjects had Angle Class I molar relationships and crowding. They were randomly divided into two groups; 30 expanded and 30 control subjects. Three-dimensional CBCT software was used to evaluate and compare treatment effects between the groups. To test for any significant differences between groups at T0 and T1, an independent t-test and paired t-tests were used.

RESULTS

The interbuccal dentoalveolar width (BDAW), interpalatal dentoalveolar width (PDAW), and interlingual dentoalveolar width (LDAW) values showed significant changes when measured from a point 3 mm coronal to the cementoenamel junction (CEJ) to 8 mm apical to the CEJ. When compared with mandibular interdentoalveolar width differences (BDAW-LDAW), significant differences (P < .05) were observed. The soft tissue width of the maxillary and mandibular teeth and alveolar bone showed no significant changes (P > .05), even with dentoalveolar arch expansion in both jaws.

CONCLUSIONS

This study indicates that Schwarz appliances primarily affect the dentoalveolar complex and have varying effects on mandibular and maxillary alveolar bone width. Also, soft tissue is not affected in the area of expansion in this research.

Facial suture synostosis of newborn Fgfr1(P250R/+) and Fgfr2(S252W/+) mouse models of Pfeiffer and Apert syndromes

Apert and Pfeiffer syndromes are hereditary forms of craniosynostosis characterized by midfacial hypoplasia and malformations of the limbs and skull. A serious consequence of midfacial hypoplasia in these syndromes is respiratory compromise due to airway obstruction. In this study, we have evaluated Fgfr1(P250R/+) and Fgfr2(S252W/+) mouse models of these human conditions to study the pathogenesis of midfacial hypoplasia. Our histologic and micro-CT evaluation revealed premature synostosis of the premaxillary-maxillary, nasal-frontal, and maxillary-palatine sutures of the face and dysplasia of the premaxilla, maxilla, and palatine bones. These midfacial abnormalities were detected in the absence of premature ossification of the cranial base at postnatal day 0. Our results indicate that midfacial hypoplasia is not secondary to premature cranial base ossification but rather primary synostosis of facial sutures. Birth Defects Research (Part A), 2011.

Hes1 is required for the development of craniofacial structures derived from ectomesenchymal neural crest cells

The cranial neural crest cells contribute extensively to the formation of skeletogenic mesenchyme in the head and neck. Hes1 functions as a repressor of basic helix-loop-helix transcription factors and is implicated in controlling the maintenance of undifferentiated cells and the timing of cell differentiation. We show here that Hes1 homozygous null mutant mice exhibit multiple craniofacial malformations including calvaria agenesis, defective anterior cranial base, shortened maxilla and mandible, and abnormal palate and tongue. In the null mutant cranium, the calvarial bones, meninges including the dura mater and skin were not formed, and the brain was therefore exposed without the outer cover. The defective anterior cranial base in the mutants was attributable to the lack of presphenoid bone and the flexed cranial base angle, which was in contrast with the flat cranial base of wild-type mice. Furthermore, in the null mutants, palatal shelf growth was impaired because of the early elevation of the palatal shelves, resulting in a narrow palate and oral cavity, which were consistently associated with a small size of the tongue. These craniofacial anomalies could be the result of the defective development of neural crest cells. Taken together, it is supposed that Hes1 signaling plays an essential role in regulating the development of various craniofacial structures derived from the cranial neural crest cells.

Inactivation of Six2 in mouse identifies a novel genetic mechanism controlling development and growth of the cranial base

The cranial base is essential for integrated craniofacial development and growth. It develops as a cartilaginous template that is replaced by bone through the process of endochondral ossification. Here, we describe a novel and specific role for the homeoprotein Six2 in the growth and elongation of the cranial base. Six2-null newborn mice display premature fusion of the bones in the cranial base. Chondrocyte differentiation is abnormal in the Six2-null cranial base, with reduced proliferation and increased terminal differentiation. Gain-of-function experiments indicate that Six2 promotes cartilage development and growth in other body areas and appears therefore to control general regulators of chondrocyte differentiation. Our data indicate that the main factors restricting Six2 function to the cranial base are tissue-specific transcription of the gene and compensatory effects of other Six family members. The comparable expression during human embryogenesis and the high protein conservation from mouse to human implicate SIX2 loss-of-function as a potential congenital cause of anterior cranial base defects in humans.

New directions in craniofacial morphogenesis

The vertebrate head is an extremely complicated structure: development of the head requires tissue-tissue interactions between derivates of all the germ layers and coordinated morphogenetic movements in three dimensions. In this review, we highlight a number of recent embryological studies, using chicken, frog, zebrafish and mouse, which have identified crucial signaling centers in the embryonic face. These studies demonstrate how small variations in growth factor signaling can lead to a diversity of phenotypic outcomes. We also discuss novel genetic studies, in human, mouse and zebrafish, which describe cell biological mechanisms fundamental to the growth and morphogenesis of the craniofacial skeleton. Together, these findings underscore the complex interactions leading to species-specific morphology. These and future studies will improve our understanding of the genetic and environmental influences underlying human craniofacial anomalies.

Oculoauriculovertebral complex with an atypical cause of obstructive sleep apnea

Oculoauriculovertebral spectrum (OAVS) is a birth defect of unknown etiology, often causing obstructive sleep apnea, due to unilateral retrognathia. We describe an adolescent sleep apnea patient, with usual and unusual signs of OAVS. Apart from mandibular hypoplasia, microtia, external auditory canal atresia and cervical vertebrae anomalies, skull base asymmetry was also noted, resulting in aberrant anatomy of the tympanic cavity, and nasopharyngeal obstruction, which was the main source of the patient's apneas. The extended craniofacial abnormalities manifested here, suggest a broader developmental impairment, exceeding the 1st and 2nd branchial arch malformation theory, which is the principal hypothesis for OAVS etiology.

Abnormal basiocciput development in CHARGE syndrome

BACKGROUND AND PURPOSE

The causative gene of the common congenital malformation referred to as CHARGE syndrome is CHD7. Affected individuals often undergo head and neck imaging to assess abnormalities of the olfactory structures, hypothalamus-pituitary axis, and inner ear. We encountered a few children with severe hypoplasia of the basiocciput during a radiologic assessment of patients with CHARGE syndrome. To our knowledge, this anomaly has not been reported. Our purpose was to evaluate the incidence and severity of this anomaly in this syndrome.

MATERIALS AND METHODS

Sagittal MR images of 8 patients with CHARGE syndrome were retrospectively reviewed by 2 radiologists who consensually evaluated the status of the basiocciput of the patients with CHARGE syndrome, as either normal or hypoplastic; and associated anomalies, which include basilar invagination, Chiari type I malformation, and syringomyelia, as either present or absent. The length between the basion (Ba) and the endo-sphenobasion (Es) and between the basion and the exo-sphenobasion (Xs) was measured on midsagittal MR images of the 8 patients and 70 age-matched controls. We searched for trends related to age in the length of Ba-Es and Ba-Xs of the control children by using a matched t test.

RESULTS

Basioccipital hypoplasia was identified in 7 of the 8 patients with CHARGE syndrome and was severe in 6. Of those, 5 had associated basilar invagination and 1 had Chiari type I malformation with syringomyelia.

CONCLUSIONS

Basioccipital hypoplasia and basilar invagination are prevalent in patients with CHARGE syndrome.

Temporal Expression of SOX9 and Type II Collagen in Spheno-Occipital Synchondrosis of Mice after Mechanical Tension Stimuli

Objective: To associate the expressions of SOX9 and type II collagen during growth in the synchondrosis with and without tensile stress in order to understand the role of these factors in the growth of cartilage in spheno-occipital synchondrosis.

Materials and Methods: Sixty 1-day-old male BALB/c mice were randomly divided into experimental and control groups. Each group was subdivided again into five different time points which were 6, 24, 48, 72, and 168 hours. Each subgroup consisted of five mice. Each mouse was sacrificed using an overdose of pentobarbitone sodium. The synchondroses were aseptically removed and incubated in a 24-well plate with or without tensile stress in tissue culture. Tissue sections were stained immunohistochemically to quantitatively analyze the expression of SOX9 and type II collagen.

Results: There was a statistically significant increase of 57% (P &lt; .001) in the expression of SOX9 between the experimental and control groups at 24 hours, followed by a significant increase of 44.4% (P &lt; .001) in the expression of type II collagen at 72 hours.

Conclusions: SOX9 may play an important role for early differentiation of chondrocytes and increase the expression of type II collagen, a major component of the extracellular matrix, during the growth of cartilage in the spheno-occipital synchondrosis.

Sagittal craniofacial growth evaluated on children dry skulls using V2 and V3 canal openings as references

The purpose of this study was to investigate the relationship between standard cephalometric landmarks and lines and those using ovale, rotundum, greater palatine and infra-orbital foramina as references. Thirty-four children dry skulls, 19 males and 15 females aged 0-6 years, were examined by computed tomography scanning. The classical cephalometric dimensions of skull base were measured from middle sagittal plane crossing over basion, nasion and sella turcica. Those of hard palate (maxilla and palatine bone) were measured from axial plane intersecting posterior nasal spine and anterior nasal spine. The dimensions between ovale and rotundum foramina, rotundum and infra-orbital foramina, greater palatine and infra-orbital foramina were determined by using constructed tomographic planes enclosing these different foramina. Biostatistical analysis using partial correlations showed that the linear variables with nerve canal openings as references are strongly related to length of both the skull base and of the hard palate. The results highlight the importance of the nerve canal openings of skull base and bone facial components in normal or pathologic craniofacial growth investigations.

Developmentally regulated expression of MSX1, MSX2 and Fgfs in the developing mouse cranial base

OBJECTIVE

To examine the expression pattern of the Fgf and Msx genes in cranial base development.

MATERIALS AND METHODS

To detect the expression of these genes, antisense riboprobes were synthesized by in vitro transcription. Radioactive in situ hybridization was performed on parasagittal sections of embryonic mouse heads.

RESULTS

Msx2 was observed in the underlying perichondrium at restricted stages. Msx1 was not observed in cranial base development. Fgf1 was localized in osteogenic cells from the time of ossification; Fgf10 was highly expressed in the occipital-vertebral joint during E13 to E14; Fgf2, Fgf7, and Fgf18 were localized in the perichondria; Fgf12 was transitorily expressed at early chondrocranium; Fgf9 was seen in the hypertrophic chondrocytes.

CONCLUSIONS

The Fgf and Msx gene expression in the cranial base was different from that of other skeletons.

Sox9 mRNA expression in the developing palate and craniofacial muscles and skeletons

BACKGROUND

SOX9 is a critical transcription factor for chondrogenesis and sex determination. Haploinsufficiency mutations of Sox9 in humans lead to campomelic dysplasia. Inactivation of Sox9 in the craniofacial region of mice results in an absence of endochondral bones and in malformation of other structures. This suggests that Sox9 plays multiple roles in craniofacial development and these remain to be elucidated. In order to study the functions of Sox9 in craniofacial development, a preliminary expression examination was performed.

MATERIAL AND METHODS

To detect the expression of Sox9 mRNA, antisense riboprobe was synthesized by in vitro transcription. Radioactive in situ hybridization was performed on sagittal and coronal sections of mice head from organogenesis to the early postnatal stage.

RESULTS

It was found that Sox9 was expressed in multiple stages and distinct processes. Besides the expression in cartilage, it was seen in the fusing stage of palatogenesis. Sox9 was also present during differentiation and maturation of craniofacial muscles. In addition, it was observed in intramembranous skeletal elements at restricted sites and stage.

CONCLUSIONS

The expression pattern suggests that Sox9 serves broad roles in craniofacial development.

Developmental expression of Dkk1-3 and Mmp9 and apoptosis in cranial base of mice

The Dickkopf (Dkk) family and Mmp9 are important for apoptosis and a number of other developmental processes. However, little is known about their roles in the development of cranial base, which is an important structure for coordinated development and growth of the craniofacial skeletons. In order to establish whether and in what way these genes are involved in cranial base development, we examined their expression patterns and cell apoptosis. Dkk1 was first seen in the perichondral mesenchyme in restricted domains from E14, and later in the migrating mesenchymal cells within the cartilage. Thereafter, it was widespread throughout the bones of the cranial base. The expression was downregulated in postnatal stages. Dkk2 was localized in the perichondral mesenchyme outlining the anterior cranial base in embryogenesis. Dkk3 was mainly detected in the occipital-vertebral joint at E13 and E14. Mmp9 transcripts were clustered in the inner layer of perichondral mesenchyme, juxtaposed with the terminally differentiated hypertrophic chondrocytes from E14. Later Mmp9-expressing cells were found at the sites of chondrocyte apoptosis. This was particularly clear at the distal ends of the synchondroses. These data indicate that Mmp9 regulates skeletogenesis in cranial base in a manner that is largely similar to that of the appendicular skeletons. Expression of Dkks suggests other roles that remain to be defined.