Skull base embryology: a multidisciplinary review

Isolated hypertelorism: Late surgical correction using the box osteotomy technique

Background

Orbital hypertelorism is a rare congenital condition caused by craniofacial malformations. It consists of complete orbital lateralization, characterized by an increase in distance (above the 95th percentile) of the inner canthal (ICD), outer canthal, and interpupillary distances. It can be approached surgically, and the main techniques are box osteotomy and facial bipartition. The surgical procedure is usually performed before the age of 8. We describe here two patients who underwent late surgical correction using the box osteotomy technique.

Case Description

Patient 1: A 13-year-old female presenting isolated hypertelorism with 5 cm ICD and left eye amblyopia. Patient 2: A 15-year-old female with orbital hypertelorism, 4.6 cm ICD, and nasal deformity. Both patients underwent orbital translocation surgery and had no neurological disorders.

Conclusion

The article reports two cases of isolated hypertelorism treated late with the box osteotomy technique. Both surgeries were successful, with no postoperative complications. It appears that it is possible to obtain good surgical results even in patients who have not been able to undergo surgery previously.

The role of sphenoid bone in basilar invagination pathophysiology

Basilar invagination (BI) is characterized by rostral dislocation of the cervical spine toward the skull base. The craniometrics of the skull base have shown significant differences among craniocervical junction malformations. The sphenoid bone is the center of the skull base; however, no study has evaluated this bone in cases of BI. This was a cross-sectional study of MRI databanks from two institutions of the author's practice between 1985 and 2020. The craniometrics of the sphenoid bone were measured in BI patients and controls. Fifty-eight MRIs were selected, including 28 BI patients and 30 controls. The mean sphenoid crest-clivus length was 32.66 ± 4.7 mm in the BI group and 29.98 ± 3.0 mm in the control group (p = 0.01). The mean sphenoid planum-top of Dorsum sellae length was 28.53 ± 3.7 mm in the BI group and 26.45 ± 3.2 mm in the control group (p = 0.02). The mean tuberculum sellae-sphenoid floor height was 18.52 ± 4.4 mm in the BI group and 21.32 ± 2.9 mm in the control group (p = 0.00). The mean sella turcica-sphenoid floor height was 10.35 ± 3.8 mm in the BI group and 12.24 ± 3.5 mm in the control group (p = 0.05). The mean clivus length was 29.81 ± 6.3 mm in the BI group and 40.86 ± 4.2 mm in the control group (p = 0.00). The mean sphenoid length was 58.34 ± 7.4 mm in the BI group and 67.31 ± 6.0 mm in the control group (p = 0.00). The mean sphenoid angle was 116.33 ± 8.7° in the BI group and 112.36 ± 6.9° in the control group (p = 0.05). The BI sphenoid bone has shorter vertical dimensions and longer horizontal measures. This morphology promotes a flattening of the sphenoid angle. The sphenoid bone is significantly altered in BI, favoring the congenital hypothesis in the pathophysiology of this disease.

Seizure caused by intraparenchymal hemorrhage from migration of mandibular dental wire through foramen ovale in a child: A case report

The foramen ovale is a structure that allows for the extracranial passage of multiple significant intracranial structures, most notably the mandibular branch of the trigeminal nerve (CN V3). Here we report the case of a 12-year-old male who presented to the emergency department (ED) with a two-day history of nausea and emesis and a one-day history of altered mental status. Prior to presentation, he started speaking only Spanish, which was unusual because he primarily speaks English. He was also showing signs of absence seizures. Computed Tomography (CT) showed his orthodontic wire had migrated and was entering his skull through the foramen ovale, terminating within the inferior temporal lobe. Associated with the wire was an intraparenchymal hemorrhage. Imaging indicated the sparing of the internal carotid artery and its major branches, suggesting the hemorrhage was likely venous in nature. The wire was then safely removed with no complications. Same day and follow-up neurologic exams all demonstrated no deficit in CN V3 or any of the other surrounding structures. To our knowledge, this is the first case described in the literature in which a foreign object penetrated the skull floor through the foramen ovale.

Rethinking the Origin of the Primary Respiratory Mechanism

Spheno-occipital synchondrosis (SOS) is the joint regarded as the most important foundation for understanding cranial osteopathy and craniosacral therapy. SOS is the origin of the primary respiratory mechanism (PRM), a movement between the posterior surface of the body of the sphenoid bone and the anterior surface of the base of the occipital bone. From the PRM perspective, an alteration of the position between the two bone surfaces would create cranial and/or craniosacral dysfunction. These positional alterations of the SOS (in adults and children) would determine specific and schematical movements of the bones of the entire skull, whose movements are recognizable by palpation by trained operators. PRM expression is influenced by other elements, such as movement of the cranial bones, inherent movement of the central nervous system, cyclic movement of cerebrospinal fluid (CSF), mechanical tension of the cranial meninges, and passive movement of the sacral bone between the iliac bones. The article reviews the most up-to-date information on the evolution of cranial sutures/joints and meninges in adulthood, the fluctuations of the CSF, brain, and spinal mass movements. Research should reconsider the motivations that induce the operator to discriminate the palpable cranial rhythmic impulse, and probably, to rethink new cranial dysfunctional patterns.

Radiologic Evaluation of the Fossa Navicularis on Dry Skull: A Comparative CBCT Study

Fossa navicularis (FN) is defined as bony depression that is not always present and is located anterior to the foramen magnum and pharyngeal tubercle on the inferior aspect of the basilar part of the occipital bone. It has been reported that FN can create an infection spread path from the pharynx to the intracranial structures. Therefore, the diagnosis of this variation is important. Although cone beam computed tomography (CBCT) diagnostic accuracy has mostly been verified in detection and quantification particularly on human skulls, there is no study comparing morphometric measurements between direct measurement on the skull and CBCT measurement. The main object of this study is to evaluate the presence of FN on dry bones and CBCT images of the same dry skull and to examine the morphometric and morphological features of this formation. Thirty-two random craniums that were made available for this study that did not have any fractures or deformities of the cranial base were examined. The sagittal diameter, transverse diameter, and depth of the FN was measured both directly on dry skulls and radiologically on CBCT images of dry skull. In addition, the shape of FN (SFN) was determined. FN was detected in 10 (31.25%) of 32 craniums examined with both modalities. It was determined that sagittal diameter of the FN, transverse diameter of the FN, depth of the FN, and the shape of FN did not show a statistically significant difference between the 2 measurements. Unlike the literature, FN was investigated on dry bones both directly and in CBCT images in this study. In contrast to previously thought the FN may be smaller according to this findings, and this small variation can be detected with CBCT images. According to this findings, it can be said that morphometric evaluations on CBCT are accurate and reliable, and CBCT is a safe method for clinical diagnosis and treatment.

Variant Bilateral Foramina of the Middle Cranial Fossa

Variations of the foramina located at the skull base can have direct clinical implications. For example, transcutaneous approaches to the trigeminal nerve using long spinal needles for treatment of trigeminal neuralgia can inadvertently enter such variant foramina and potentially result in hemorrhage. Therefore, knowledge of such variant foramina is important to the clinician treating or diagnosing patients based on imaging of this region. We report an adult male skull found to have unusual foramina located at the skull base. The foramina were located approximately 3.1 cm lateral to the plane of the foramen rotundum and foramen ovale. The left foramen had a diameter of 0.82 mm and the right foramen had a diameter of 0.77 mm. Both foramina opened up just medial to the sphenotemporal suture into the roof of the infratemporal fossa. Additionally, each foramen was the most lateral of a larger collection of foramina found to exit the skull base but confluent with the diploic space of the greater wind of the sphenoid and not with the floor of the middle cranial fossa. This group of openings, including the most lateral which communicated with the middle cranial fossa, were lateral to the lateral plate of the pterygoid process. Knowledge of variant foramina of the skull base is important to clinicians treating patients with pathology of this region. To our knowledge, foramina as described herein have not been previously reported in the extant medical literature.

Camurati-Engelmann disease combined with transethmoidal meningoencephalocele: illustrative case

BACKGROUND

Camurati-Engelmann disease (CED) is a rare disorder characterized by progressive cranial hyperostosis and diaphyseal sclerosis of the long bones. Chronic intracranial hypertension gradually occurs due to progressive cranial vault hyperostosis.

OBSERVATIONS

A 57-year-old man who had been diagnosed with CED at 9 years old suddenly developed cerebrospinal fluid rhinorrhea. A bone defect of the right cribriform plate and protrusion of brain tissue from the right cribriform plate into the right nasal cavity were identified. The patient underwent endoscopic resection of the meningoencephalocele combined with the bath-plug procedure. After surgery, cerebrospinal fluid rhinorrhea disappeared.

LESSONS

Chronic intracranial hypertension due to progressive cranial vault hyperostosis in CED may cause a bone defect and meningoencephalocele in the anterior skull base, resulting in cerebrospinal fluid rhinorrhea.

Clivus pathologies from diagnosis to surgical multidisciplinary treatment. Review of the literature

The Clivus is a bone that lies in a central position of the skull base, and it is a crucial point that splits and connects different anatomical compartments at the same time. There is significant variability of diseases involving the clivus, from neoplasms to non-neoplastic, inflammatory or traumatic lesions. Each of these is rare in frequency, and this heterogeneity contributes to yield the management even more challenging. Clival pathologies can be asymptomatic or have manifestations ranging from aspecific headache to cranial nerves palsies, till life-threatening complications as cerebrospinal fluid rhinorrhoea, meningitis or brain abscess. There isn’t an univocal endorsement among experts with regard to the best approaches to manage the clivus. The paths described are many, the main division is between the transclival and transcranial lateral approaches. We performed a review of the literature, thus highlighting how authors seem to suggest that the surgical approach shouldn’t be chosen aprioristically, but based on a patient centred analysis, considering the combination of multiple surgical corridors. From diagnosis to surgery and medical therapy, clival pathologies require a team of multidisciplinary experts to ensure the best standard of treatment and higher survival rate.

Skeletal stem and progenitor cells maintain cranial suture patency and prevent craniosynostosis

Cranial sutures are major growth centers for the calvarial vault, and their premature fusion leads to a pathologic condition called craniosynostosis. This study investigates whether skeletal stem/progenitor cells are resident in the cranial sutures. Prospective isolation by FACS identifies this population with a significant difference in spatio-temporal representation between fusing versus patent sutures. Transcriptomic analysis highlights a distinct signature in cells derived from the physiological closing PF suture, and scRNA sequencing identifies transcriptional heterogeneity among sutures. Wnt-signaling activation increases skeletal stem/progenitor cells in sutures, whereas its inhibition decreases. Crossing Axin2LacZ/+ mouse, endowing enhanced Wnt activation, to a Twist1+/- mouse model of coronal craniosynostosis enriches skeletal stem/progenitor cells in sutures restoring patency. Co-transplantation of these cells with Wnt3a prevents resynostosis following suturectomy in Twist1+/- mice. Our study reveals that decrease and/or imbalance of skeletal stem/progenitor cells representation within sutures may underlie craniosynostosis. These findings have translational implications toward therapeutic approaches for craniosynostosis.

The Skull's Girder: A Brief Review of the Cranial Base

The cranial base is a multifunctional bony platform within the core of the cranium, spanning rostral to caudal ends. This structure provides support for the brain and skull vault above, serves as a link between the head and the vertebral column below, and seamlessly integrates with the facial skeleton at its rostral end. Unique from the majority of the cranial skeleton, the cranial base develops from a cartilage intermediate-the chondrocranium-through the process of endochondral ossification. Owing to the intimate association of the cranial base with nearly all aspects of the head, congenital birth defects impacting these structures often coincide with anomalies of the cranial base. Despite this critical importance, studies investigating the genetic control of cranial base development and associated disorders lags in comparison to other craniofacial structures. Here, we highlight and review developmental and genetic aspects of the cranial base, including its transition from cartilage to bone, dual embryological origins, and vignettes of transcription factors controlling its formation.

Study of the growth and shape of the brain and cranial base during the first two years of life

Ontogeny of the cranial base and the brain integrates data on growth, maturation and ontogenetic allometry of these two systems in the course of development. The aim of our work was to study the ontogeny of the cranial base and the brain in order to understand their growth dynamic and shape changes using a traditional morphometric approach in individuals with normal (non-pathological) development.

MATERIEL AND METHOD

Forty-seven infants having been included in the unexpected infant death french protocol were analyzed. Medical imaging (CT and MRI) exams, followed by an autopsy and pathology examination allowed us to include only infants free from brain disease or pathology affecting growth.

RESULTS

Testing of measurement reliability validated 12 distances and 3 angles as well as the positioning of the landmarks that had been used to obtain the distances and the angles. No correlation between sex and the various variables studied was found. However, a correlation was observed between these variables and age, making it possible to propose a growth curve. A medium to strong correlation was found between brain variables and the bone variables of the cranial base, underlining the parallel development of the two systems.

CONCLUSION

Our study, carried out in a rigorously selected population of infants, presents a fundamental approach to the study of ontogenesis.

Assessing the abilities of senior otolaryngology residents and graduated otolaryngologists in recognizing skull base elements in axial CT scan: proposing a new method for differentiating superior orbital fissure and optic canal

BACKGROUND AND OBJECTIVES

The aim of this study was to evaluate the ability of recognizing some important elements of the skull base in axial CT-scan cuts, including the optic canal (OC), superior orbital fissure (SOF), vidian canal (VC), foramen rotundum (FR), jugular foramen (JF) and hypoglossal canal (HC).

METHODS

In this study, 25 otolaryngology residents and 25 recently graduated otolaryngologists were evaluated in terms of their recognition of skull base elements, using 30 axial CT-scan cuts. Two months later, the exam related to skull base CT scans was taken in groups after a brief anatomy courses for otolaryngology residents.

RESULTS

The percentage of correct answers from otolaryngology residents regarding OC, SOF, VC, FR, JF, and HC in the first exam were 74 ± 26, 47 ± 34, 65 ± 30, 41 ± 38, 58 ± 26, and 68 ± 32, respectively. The correct answer for each element was similar between groups, and the differences were not statistically significant (p > 0.05). p value for the differences observed regarding the percentage of correct answers for the second exam between trained otolaryngology residents and recent otolaryngology graduates regarding OC and JF was no significant (p > 0.05) but significant for the other elements with better result in trained otolaryngology residents and most for SOF (p > 0.0001).

CONCLUSION

This study showed that the ability of recognition for the mentioned elements in axial CT-scan cuts was low among otolaryngology residents and graduated otolaryngologists. The proposed novel method for distinguishing SOF from OC had a powerful and long-lasting effect on trainee.

Symptomatic Internal Carotid Agenesis in Children

Carotid artery agenesis is a rare congenital anomaly, and there are controversies in the leading cause for it. We present a 6-year-old girl with resolved focal neurological ischemic stroke that showed bilateral internal carotid artery (ICA) agenesis. Through this paper, we highlight the carotid canal congenital obliteration hypothesis as it may be a risk for such finding.

Morphometric and Anatomic Variations of Foramen Ovale in Human Skull and Its Clinical Importance

Objective:

There is a paucity of information regarding the specific anatomy and clinical significance of variations of foramen ovale (FO). The present study was undertaken to define this anatomy in more detail and to review the literature regarding these anatomic variations.

Materials and Methods:

A total of 124 adult human dry skulls were analyzed for the variations in appearance and number of FO being noted. The length and width of the FO of both sides were determined using digital vernier calipers and area (A) was also calculated and analyzed.

Results:

Of 82 adult skulls, the values for the right side was 7.64 ± 1.194 mm, 5.128 ± 0.827 mm, and 30.808 ± 7.545 mm² and for the left side the values was 7.561 ± 1.123 mm, 5.244 ± 0.950 mm, and 31.310 ± 8.262 mm², respectively, for the mean length, width, and area of the FO. The shape of foramen was typically ovale in most of the skulls (56.70%) with some bony variations such as spine, tubercles, bony bridge/bar, and confluence.

Conclusion:

Such variants in the FO could interfere with transcutaneous needle placement into the FO or distort anatomic relationships during approaches to the cranial base.

The Comparison of the Right and Left Sigmoid Sinus Cross-Sectional Areas in Fetal Period and the Factors Affecting the Venous Dominance

OBJECTIVES

Skull base is an important and a challenging area for surgeons. Success in skull base surgery depends on various factors such as pre-operative evaluation, appropriate surgical technique, anesthesia duration, intraoperative neuromonitorization and wound care.

MATERIALS AND METHODS

This study was performed in the Anatomy dissection laboratory of M.U. Medical Faculty (Ethical committee approval number 2010-103). Twelve fetuses between 17-33 gestational weeks fixed with formaldehyde were enrolled to the study.

RESULTS

This study was planned to investigate the cross sectional areas of the sigmoid sinus in three levels to compare the right-left sides and the probable relationship among the levels in fetuses to further delineate the developmental factors on jugular foramen asymmetry. The cross-sectional measurements of sigmoid sinus lumen were done on 3 levels which are described as A1 level; sinodural angle, A2 level; the midpoint between the sinodural angle and endocranial orifice and A3 level as the entrance (endo-cranial orifice) of the jugular foramen. There is a strong positive correlation between left (L) A1 and L A2 and also the same for L A1 and right (R) A2. These strong and positive correlations are all valid between L A2-L A3, L A2-R A2, L A2-R A3, L A3-R A3, R A1-R A2.

CONCLUSION

Multicenter studies would be beneficial to investigate the topic with greater number of fetuses also on the different regions for genetic differences.

Repair of a Transclival Meningocele Through a Transoral Approach: Case Report and Literature Review

BACKGROUND

Transclival meningoceles and related primary spontaneous cerebrospinal fluid leaks at the clivus are extremely rare lesions, with only a few cases reported in the literature.

CASE DESCRIPTION

An infant presented with nasal airway obstruction and meningitis secondary to cerebrospinal fluid leak from a transclival meningocele. The radiologic investigation and surgical repair of the lesion are reported, along with intraoperative findings. Basic anatomy, embryology, and development of the clivus are reviewed to clarify the relationship of anatomic variants with the formation of transclival meningoceles.

CONCLUSIONS

Transclival meningocele should be considered in patients with spontaneous cerebrospinal fluid rhinorrhea. The existing classification of meningoencephaloceles based on the location of the defect in the cranium should probably be reconsidered, taking into consideration the described entity.

Differential evolution of cerebral and cerebellar fossae in recent Homo: A new methodological approach

The endocranium shows the influence of the shape and development of brain tissues and overall brain modifications. During the late Upper Pleistocene and Holocene smaller brains appeared and the higher position of endinion relative to inion might indicate changes in cerebellar and occipital lobes. In previous studies, the depths of the cerebral and cerebellar fossae were not specifically considered; new tools for quantitatively measuring these irregular, problematic curved areas need to be developed. This paper's main objective is to investigate to what degree changes in the fossae's depths of extant humans have occurred with respect to fossil anatomically modern humans (AMH) and older Homo species. The proportions of the occipital and nuchal planes are compared measuring the inner and outer surfaces of the bone. Additionally, this paper proposes a quantitative geometric methodology based on endocranial landmarks that create a plane with which to measure the position of the deepest part of the fossa: it represents a curvature maxima - concavity - associated with local structures. The four points thus obtained could be framed in Bookstein's Type II landmarks but without biomechanical implication. Through univariate, bivariate and multivariate analyses (principal components analysis) of raw and size-corrected data we study the differential evolution in recent Homo species, which presents a more vertical occipital area than ancient fossils. Our results corroborate this derived trait; additionally, we have observed a tendency towards a relative decrease in the depth of the cerebral fossae and maintenance of the cerebellar fossae.

A comprehensive review of the clivus: anatomy, embryology, variants, pathology, and surgical approaches

INTRODUCTION

The clivus is a bony structure formed by the fusion of the basioccipital and basispheniod bone at the sphenooccipital synchondrosis. This downward sloping structure from the dorsum sellae to the foramen magnum is derived from mesoderm and ectoderm properties.

METHODS

This comprehensive review of the clivus will discuss its basic anatomy, embryology, pathological findings, and surgical implications. The clivus is an endochondral bone, formed under two processes; first, a cartilaginous base is developed, and it is secondly reabsorbed and replaced with bone. Knowledge of its embryological structure and growth of development will clarify the pathogenesis of anatomical variants and pathological findings of the clivus.

CONCLUSIONS

Understanding the anatomy including proximity to anatomical structures, adjacent neurovasculature properties, and anatomical variants will aid neurosurgeons in their surgical management when treating pathological findings around the clivus.

Bone development in laboratory mammals used in developmental toxicity studies

Evaluation of the skeleton in laboratory animals is a standard component of developmental toxicology testing. Standard methods of performing the evaluation have been established, and modification of the evaluation using imaging technologies is under development. The embryology of the rodent, rabbit, and primate skeleton has been characterized in detail and summarized herein. The rich literature on variations and malformations in skeletal development that can occur in the offspring of normal animals and animals exposed to test articles in toxicology studies is reviewed. These perturbations of skeletal development include ossification delays, alterations in number, shape, and size of ossification centers, and alterations in numbers of ribs and vertebrae. Because the skeleton is undergoing developmental changes at the time fetuses are evaluated in most study designs, transient delays in development can produce apparent findings of abnormal skeletal structure. The determination of whether a finding represents a permanent change in embryo development with adverse consequences for the organism is important in study interpretation. Knowledge of embryological processes and schedules can assist in interpretation of skeletal findings.

The Measurement of Various Anatomical Structures and Assessment of Morphometric Development of Fetal Skull Base

BACKGROUND

As the skull base has a complex anatomy, we underline the importance of anomalies for side asymmetry. It is useful to investigate relationship between anatomical structures for the surgical procedure orientations. Dural adherence, enlarged superior petrosal sinus, influence of neural crest cells, and cranial base ossification are among the factors in morphometric growth on skull base.

MATERIAL AND METHODS

Twenty-five fetuses of an estimated gestational age ranging from 17 to 34 weeks were studied in the Anatomy Laboratory of Mersin University Medical Faculty. Craniotomy was made to each fetus and brain hemispheres were dissected. We put plates, passing from the external points of lateral and anterior-posterior borders of fetus heads that are perpendicular to each other. An analytical calculation was formulated for the angle of foraminae to the root of zygoma by using different formulations depending on their posterior or anterior location to the root of zygoma. Statistical method was based on correlation analysis, simple regression, independent 2 group t tests, SPSS20.0, and MedCalc 11.5 (MedicReS, New York, NY).

RESULTS

Neither side dominance for the jugular foramen, nor the differences of foramen rotundum, spinosum, and ovale to anterior skull wall, root of zygoma, and to midline were found to be significant.

CONCLUSION

There is a debate on asymmetry of foramina of the skull base. No certain consensus about the initiation time and the causes of asymmetry in the past was documented. Studies are to be encouraged to further enlighten pre-postnatal factors affecting the fetal skull base morphometrism.

Genetically induced abnormal cranial development in human trisomy 18 with holoprosencephaly: comparisons with the normal tempo of osteogenic-neural development

Craniofacial malformations are common congenital defects caused by failed midline inductive signals. These midline defects are associated with exposure of the fetus to exogenous teratogens and with inborn genetic errors such as those found in Down, Patau, Edwards' and Smith-Lemli-Opitz syndromes. Yet, there are no studies that analyze contributions of synchronous neurocranial and neural development in these disorders. Here we present the first in-depth analysis of malformations of the basicranium of a holoprosencephalic (HPE) trisomy 18 (T18; Edwards' syndrome) fetus with synophthalmic cyclopia and alobar HPE. With a combination of traditional gross dissection and state-of-the-art computed tomography, we demonstrate the deleterious effects of T18 caused by a translocation at 18p11.31. Bony features included a single developmentally unseparated frontal bone, and complete dual absence of the anterior cranial fossa and ethmoid bone. From a superior view with the calvarium plates removed, there was direct visual access to the orbital foramen and hard palate. Both the eyes and the pituitary gland, normally protected by bony structures, were exposed in the cranial cavity and in direct contact with the brain. The middle cranial fossa was shifted anteriorly, and foramina were either missing or displaced to an abnormal location due to the absence or misplacement of its respective cranial nerve (CN). When CN development was conserved in its induction and placement, the respective foramen developed in its normal location albeit with abnormal gross anatomical features, as seen in the facial nerve (CNVII) and the internal acoustic meatus. More anteriorly localized CNs and their foramina were absent or heavily disrupted compared with posterior ones. The severe malformations exhibited in the cranial fossae, orbital region, pituitary gland and sella turcica highlight the crucial involvement of transcription factors such as TGIF, which is located on chromosome 18 and contributes to neural patterning, in the proper development of neural and cranial structures. Our study of a T18 specimen emphasizes the intricate interplay between bone and brain development in midline craniofacial abnormalities in general.

Morphology of the foramen magnum in syndromic and non-syndromic brachycephaly

PURPOSE

The shape and size of the foramen magnum (FM) can be altered in craniosynostoses. However, few studies have investigated these changes. In this paper, we investigate the morphology of the foramen magnum in syndromic and non-syndromic brachycephaly.

METHODS

Surface area, anteroposterior (AP) diameter, and transverse diameters of the FM were measured on high-resolution CT scans in children with Crouzon (25), Pfeiffer (21), Apert (26), Saethre-Chotzen (7) syndromes, and isolated bicoronal synostosis (9) and compared to an age-matched control group (30).

RESULTS

A significantly smaller FM surface area was observed in Crouzon (6.3 ± 1.7 cm(2)) and Pfeiffer (6.4 ± 2.3 cm(2)) syndromes as compared to the control group (7.4 ± 1.3 cm(2), p = 0.006 and p = .017, respectively). In comparison to the control group, no statistically significant alteration in FM surface area was noted in patients with Apert, Saethre-Chotzen, or isolated bicoronal synostosis (p = 0.37, p = 0.71, p = 0.40 respectively). The transverse diameter of FM was significantly smaller in Crouzon, Pfeiffer, and Apert syndromes compared to the control group (p = 0.005, p = 0.002, p = 0.03 respectively). In Saethre-Chotzen and isolated bicoronal synostosis, no difference in transverse diameter was demonstrated. Among all groups, only Crouzon syndrome showed reduced anteroposterior diameter as compared to controls (p = 0.005). In Pfeiffer and Apert syndromes, there was elongation of the shape of the FM with a relatively narrowed width as demonstrated in a significantly increased AP to transverse diameter ratio (p = 0.002 and p = 0.019, respectively).

DISCUSSION AND CONCLUSIONS

The FM shape and area is significantly altered in fibroblast growth factor receptor (FGFR)-related brachycephaly syndromes (Crouzon, Pfeiffer, and Apert), whereas in patients with Saethre-Chotzen syndrome (TWIST-1 mutation) and isolated non-syndromic bicoronal synostosis, the shape and mean FM area was not statistically different from that of normals. This study brings to light the important role of FGFRs on FM growth and shape. TWIST-1 mutation (Saethre-Chotzen syndrome) does not appear to have an important effect in shaping the FM.