Correction of Coronal Suture Synostosis Using Suture and Dura Mater Allografts in Rabbits With Familial Craniosynostosis

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.

Mice lacking the conserved transcription factor Grainyhead-like 3 (Grhl3) display increased apposition of the frontal and parietal bones during embryonic development

BACKGROUND

Increased apposition of the frontal and parietal bones of the skull during embryogenesis may be a risk factor for the subsequent development of premature skull fusion, or craniosynostosis. Human craniosynostosis is a prevalent, and often serious embryological and neonatal pathology. Other than known mutations in a small number of contributing genes, the aetiology of craniosynostosis is largely unknown. Therefore, the identification of novel genes which contribute to normal skull patterning, morphology and premature suture apposition is imperative, in order to fully understand the genetic regulation of cranial development.

RESULTS

Using advanced imaging techniques and quantitative measurement, we show that genetic deletion of the highly-conserved transcription factor Grainyhead-like 3 (Grhl3) in mice (Grhl3 ^-/- ) leads to decreased skull size, aberrant skull morphology and premature apposition of the coronal sutures during embryogenesis. Furthermore, Grhl3 ^-/- mice also present with premature collagen deposition and osteoblast alignment at the sutures, and the physical interaction between the developing skull, and outermost covering of the brain (the dura mater), as well as the overlying dermis and subcutaneous tissue, appears compromised in embryos lacking Grhl3. Although Grhl3 ^-/- mice die at birth, we investigated skull morphology and size in adult animals lacking one Grhl3 allele (heterozygous; Grhl3 ^+/- ), which are viable and fertile. We found that these adult mice also present with a smaller cranial cavity, suggestive of post-natal haploinsufficiency in the context of cranial development.

CONCLUSIONS

Our findings show that our Grhl3 mice present with increased apposition of the frontal and parietal bones, suggesting that Grhl3 may be involved in the developmental pathogenesis of craniosynostosis.

Rapid re-synostosis following suturectomy in pediatric mice is age and location dependent

Craniosynostosis is the premature fusion of the cranial sutures early in development. If left untreated, craniosynostosis can lead to complications resulting from cranial deformities or increased intracranial pressure. The standard treatment involves calvarial reconstruction, which in many cases undergoes rapid re-synostosis. This requires additional surgical intervention that is associated with a high incidence of life threatening complications. To better understand this rapid healing, a pediatric mouse model of re-synostosis was developed and characterized. Defects (1.5mm by 2.5mm) over the posterior frontal suture were created surgically in weanling (21 days post-natal) and adolescent (50 days post-natal) C57Bl/6J mice. In addition, defects were created in the frontal bone lateral to the posterior frontal suture. The regeneration of bone in the defect was assessed using advanced image processing algorithms on micro-computed tomography scans. The genes associated with defect healing were assessed by real-time PCR of mRNA isolated from the tissue present in the defect. The results showed that the weanling mouse healed in a biphasic process with bone bridging the defect by post-operative (post-op) day 3 followed by an increase in the bone volume on day 14. In adolescent mice, there was a delay in bone bridging across the defect, and no subsequent increase in bone volume. No bridging of the defect by 14 days post-op was seen in identically sized defects placed lateral to the suture in both weanling and adolescent animals. This study demonstrates that bone regeneration in the cranium is both age and location dependent. Rapid and robust bone regeneration only occurred when the defect was created over the posterior frontal suture in immature weanling mice.

Craniosynostosis: molecular pathways and future pharmacologic therapy

Craniosynostosis describes the premature fusion of one or more cranial sutures and can lead to dramatic manifestations in terms of appearance and functional impairment. Contemporary approaches for this condition are primarily surgical and are associated with considerable morbidity and mortality. The additional post-operative problems of suture refusion and bony relapse may also necessitate repeated surgeries with their own attendant risks. Therefore, a need exists to not only optimize current strategies but also to develop novel biological therapies which could obviate the need for surgery and potentially treat or even prevent premature suture fusion. Clinical studies of patients with syndromic craniosynostosis have provided some useful insights into the important signaling pathways and molecular events guiding suture fate. Furthermore, the highly conserved nature of craniofacial development between humans and other species have permitted more focused and step-wise elucidation of the molecular underpinnings of craniosynostosis. This review will describe the clinical manifestations of craniosynostosis, reflect on our understanding of syndromic and non-syndromic craniosynostoses and outline the different approaches that have been adopted in our laboratory and elsewhere to better understand the pathogenesis of premature suture fusion. Finally, we will assess to what extent our improved understanding of the pathogenesis of craniosynostosis, achieved through laboratory-based and clinical studies, have made the possibility of a non-surgical pharmacological approach both realistic and tangible.

Matrices and scaffolds for drug delivery in dental, oral and craniofacial tissue engineering

Current treatments for diseases and trauma of dental, oral and craniofacial (DOC) structures rely on durable materials such as amalgam and synthetic materials, or autologous tissue grafts. A paradigm shift has taken place to utilize tissue engineering and drug delivery approaches towards the regeneration of these structures. Several prototypes of DOC structures have been regenerated such as temporomandibular joint (TMJ) condyle, cranial sutures, tooth structures and periodontium components. However, many challenges remain when taking in consideration the high demand for esthetics of DOC structures, the complex environment and yet minimal scar formation in the oral cavity, and the need for accommodating multiple tissue phenotypes. This review highlights recent advances in the regeneration of DOC structures, including the tooth, periodontium, TMJ, cranial sutures and implant dentistry, with specific emphasis on controlled release of signaling cues for stem cells, biomaterial matrices and scaffolds, and integrated tissue engineering approaches.

Morphometric methods to evaluate craniofacial growth: study in rabbits

OBJECTIVES

The purpose of this study was to evaluate the reliability of direct and indirect measurement methods, with a view to standardizing morphometry instruments.

METHODS

Dry skulls of 30 New Zealand rabbits were used. Measurements were made with a transparent flexible plastic ruler, an EKG calliper and a digital calliper, as well as with computerized tomography and lateral radiographs for direct and indirect analysis of distances and angles.

RESULTS

The different instruments studied showed only partial agreement.

CONCLUSIONS

A standardized and reliable direct or indirect morphometry method for the craniofacial skeleton of rabbits still has not been determined.

Relationship of brain and skull in pre- and postoperative sagittal synostosis

Models of vertebrate skull evolution stress the coordinated developmental relationship between the skull and the brain that it houses. This study investigates the relationship between altered skull morphology and brain morphology in premature fusion of the cranial sagittal suture (isolated sagittal synostosis; ISS), a condition associated with dysmorphology of both neurocranium and brain. Although the skull displays a more normal shape following reconstructive cranial vault surgery, effects of this surgery on the brain have not been investigated. Landmark coordinate data were collected from three-dimensional magnetic resonance imaging reconstructions of the brain in a sample of ISS patients and an age-matched unaffected cohort. These data were analysed using Euclidean distance matrix analysis (EDMA). Results show that the brain in ISS is dysmorphic preoperatively, displaying a posteriorly directed neural expansion that does not 'worsen' with growth. Postoperatively, the brain in ISS displays a more globular shape overall as compared with the preoperative morphology, but differs from normal in its subcortical morphology. These results show that the ISS brain is altered following neurocranial surgery, but does not more closely approximate that of unaffected individuals. This suggests that although the brain is affected by manipulation of the skull, it retains a growth pattern that is, at least in part, independent of the skull.

Cytokine therapy for craniosynostosis

The birth prevalence of craniosynostosis (premature suture fusion) is 300-500 per 1,000,000 live births. Surgical management involves the release of the synostosed suture. In many cases, however, the suturectomy site rapidly reossifies, further restricts the growing brain and alters craniofacial growth. This resynostosis requires additional surgery, which increases patient morbidity and mortality. New findings in bone biology and molecular pathways involved with suture fusion, combined with novel tissue engineering techniques, may allow the design of targeted and complementary therapies to decrease complications inherent in high-risk surgical procedures. This paper selectively reviews recent advances in i) identifying genetic mutations and the aetiopathogenesis of a number of craniosynostotic conditions; ii) cranial suture biology and molecular biochemical pathways involved in suture fusion; and iii) the design, development and application of various vehicles and tissue engineered constructs to deliver cytokines and genes to cranial sutures. Such biologically based therapies may be used as surgical adjuncts to rescue fusing sutures or help manage postoperative resynostosis.

Tissue-engineered rabbit cranial suture from autologous fibroblasts and BMP2

Craniosynostosis is a congenital disorder of premature ossification of cranial sutures, occurring in one of approximately every 2500 live human births. This work addressed a hypothesis that a cranial suture can be tissue-engineered from autologous cells. Dermal fibroblasts were isolated subcutaneously from growing rabbits, culture-expanded, and seeded in a gelatin scaffold. We fabricated a composite tissue construct by sandwiching the fibroblast-seeded gelatin scaffold between two collagen sponges loaded with recombinant human BMP2. Surgically created, full-thickness parietal defects were filled with the composite tissue construct in the same rabbits from which dermal fibroblasts had been obtained. After four-week in vivo implantation, there was de novo formation of tissue-engineered cranial suture, microscopically reminiscent of the adjacent natural cranial suture. The tissue-engineered cranial suture showed radiolucency on radiographic images, in contrast to radio-opacity of microscopically ossified calvarial defects filled with fibroblast-free, BMP2-loaded constructs. This approach may be refined for tissue engineering of cranial sutures for craniosynostosis patients.

Neurocranial suture autotransplantation and periosteal dura stripping to provide a passive growth site in craniosynostosis--a case report

AIM

The behaviour of a neurocranial suture autograft in a plagiocephalic infant is described.

PATIENT AND METHODS

In a 7-month-old girl, born with right-sided unicoronal synostosis, part of the left-sided unicoronal suture was transplanted to the right-sided synostosectomy site. Also, in the pathological area, the periosteal 'layer' of the dura was surgically removed. The suture autotransplantation was integrated into the classical concept of radical remodelling, planned in a computer design environment. Growth of the suture was monitored by CT.

RESULTS

Suture patency and osseous growth within the autograft could be demonstrated over a 1-year period.

CONCLUSION

Neurocranial suture autotransplantation together with the prohibition of fusion-inducing dural signals seems to be a promising technique in the treatment of certain premature synostoses. This warrants a prospective clinical trial.

Management of craniosynostosis

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Review the etiopathogenesis of craniosynostosis and craniofacial anomalies. 2. Develop a basic understanding of the clinical manifestations and diagnosis of craniofacial anomalies. 3. Describe the surgical principles of managing craniosynostosis and craniofacial anomalies.Craniosynostosis, or the premature closure of calvarial sutures, results in deformed calvaria at birth. Although the etiology of craniosynostosis is currently unknown, animal experiments and a recent interest in molecular biology point toward interplay between the dura and the underlying brain. This interaction occurs by means of a local alteration in the expression of transforming growth factor, MSX2, fibroblast growth factor receptor, and TWIST. The fused suture restricts growth of the calvaria, thus leading to a characteristic deformation, each associated with a different type of craniosynostosis. Uncorrected craniosynostosis leads to a continuing progression of the deformity, and in some cases, an elevation of intracranial pressure. Clinical examination should include not only an examination of the skull but also a general examination to rule out the craniofacial syndromes that accompany craniosynostosis. Because deformational plagiocephaly, or plagiocephaly without synostosis, occurs secondary to sleeping in the supine position during the early perinatal period, the physician should be aware of this abnormality. Treatment for deformational plagiocephaly is conservative when compared with treatment for craniosynostosis, which requires surgery. Appropriate investigations should include genetic screening, radiologic examination with a computerized tomographic scan, and neurodevelopmental analysis. Surgical intervention should be performed during infancy, preferably in the first 6 months of postnatal life, to prevent the further progression of the deformity and possible complications associated with increased intracranial pressure. The principles of surgical intervention are not only to excise the fused suture but also to attempt to normalize the calvarial shape. Long-term follow-up is critical to determine the effect of the surgical outcome.

Unicoronal suture autotransplantation in the rabbit

INTRODUCTION

Our hypothesis was that a neurocranial suture autograft will, when shielded from dura, grow and be incorporated into the calvarium.

METHODS

Growth was monitored by marker separation in three isohistogenic groups of rabbits, between postnatal days 9 and 90. In order to simulate increased neurocapsular expansion force, the left-sided coronal suture of a group of 20 rabbits was immobilised with a resorbable suture on gestational day 25. The other group of 10 rabbits was sham-operated. On postnatal day 9, 10 of the experimental rabbits underwent transplantation of the suture contralateral to the defect resulting from extirpation of the immobilised suture. The transplant was shielded from dural influence by a platinum foil.

RESULTS

The growth of the immobilised coronal sutures was severely impaired, and also that of the contralateral unicoronal sutures to a lesser extent. A significant catch-up of growth occurred in the transplanted unicoronal sutures. Overgrowth occurred at the donor sites.

CONCLUSION

The results allow us to consider suture transplantation combined with endosteal dura stripping in craniosynostosis surgery.

Cranial base changes following coronal suturectomy in craniosynostotic rabbits

It has been suggested that surgical release of synostosed sutures may ameliorate various cranial base abnormalities in craniosynostotic patients. The present study was designed to test this hypothesis in a rabbit model with familial coronal suture synostosis (CSS). Data were collected from 56 New Zealand White rabbits: 32 unaffected controls, 11 with unoperated CSS, and 13 with CSS released by suturectomy performed at 25 days of age. Serial radiographs were taken at 25, 42 and 84 days. Linear, angular and triangular shape cranial base measurements were compared using ANOVA and tensor biometric analysis. Results revealed that at 84 days, both groups of CSS rabbits had significantly (p < 0.05) different anterior and total cranial base lengths, flatter cranial base angles, and dysmorphic anterior cranial base shapes when compared with normals. Significant (p < 0.05) differences were noted only for palatal and cranial base angles and posterior cranial base shape between CSS rabbits with and without suturectomy. However, significant (p < 0.05) changes were noted between pre- and postoperative measurements in posterior and total cranial base lengths and anterior and posterior cranial base shapes in CSS rabbits with suturectomy. Results revealed that surgical release of synostosed coronal sutures through suturectomy did not normalize cranial base growth patterns in CSS rabbits. These findings may be explained by the relatively late age of surgical release or suturectomy site resynostosis with continued dysmorphic cranial base growth. Alternatively, cranial base abnormalities seen in CSS rabbits may be early primary malformations, not secondary deformations amenable to surgical modification.

Coronal suturectomy does not cause acute postoperative displacement in the cranial bases of craniosynostotic rabbits

Approximately 300 to 500 infants per 1,000,000 have prematurely fused cranial sutures (craniosynostosis). Craniosynostosis can result in increased intracranial pressure and craniofacial deformities, which often require extensive and costly craniofacial surgery. Because the neurocranium and basicranium are developmentally interrelated, understanding their influence on one another is important for surgical planning. Although surgery has been found to have long-term effects on the cranial bases of craniosynostotic human beings and rabbits, the biological mechanisms behind these effects remain uncertain. Some researchers have suggested that the surgical release of synostosed sutures alters long-term growth patterns, resulting in cranial base differences between craniosynostotic individuals who undergo surgery and those who do not. Additionally, some investigators have proposed that an acute and surgically related displacement of basicranial elements may contribute to the observed differences. The current study examines acute postoperative changes in four lengths, three angles, and three triangles between cranial base landmarks in a sample of seven New Zealand white rabbits with familial nonsyndromic craniosynostosis. Results indicate that suturectomy caused no statistically significant (P < 0.05) acute length, angular, or shape differences in the cranial base. Thus, previous long-term cranial base differences found between rabbits that were operated on and those that were not were probably not caused by an acute displacement of skeletal elements as a result of surgery. These findings suggest that postoperative cranial base changes may be related more to chronically altered growth patterns than to acutely altered changes in intracranial pressure or dural tension.