A new in utero sheep model for unilateral coronal craniosynostosis

Advances in Fetal Surgery: Current and Future Relevance in Plastic Surgery

Scarless healing has long been the holy grail for plastic surgery. While historically fetal surgery has tempted plastic surgeons with the allure of scarless correction of congenital abnormalities, the risks far outweighed the benefits and these interventions never materialized. Current advances in fetal surgery with minimally invasive fetoscopic surgery have made these early fetal interventions safer, leading to expanding applications. While the plastic surgeon's role is limited as of yet, this article provides a review of the history of fetal surgery and the advances that may become relevant to the future plastic surgeon.

Unilateral Coronal Synostosis: A Histomorphometric Study

Objective

This histomorphometric study compared the open and prematurely fused side of the coronal suture in subjects with unilateral coronal synostosis (UCS).

Methods

Sutures and parasutural bone were obtained from seven subjects with nonsyndromic UCS during operative correction at 3 to 24 months of age. Histological and cellular analyses were performed for the affected and open sutures. Specimens were examined by light and polarizing microscopy. Sutural patterns, osseous morphology, calvarial thickness, tartrate-resistant acid phosphatase (TRAP)-positive cells, and marrow spaces were evaluated histomorphologically, qualitatively, and semiquantitatively. Histomorphometry was performed to determine total projected area of marrow space as a percentage of unit area, total number of TRAP-positive cells per specimen, and perisutural cranial thickness.

Results

Polarizing microscopy showed that affected sutures were composed of more lamellar bone than the normal sutures. By light microscopy, the clinically fused sutures were 1.7-fold thicker (p < .02), had twofold larger marrow spaces (p < .0006), and contained sixfold more TRAP-positive osteoclasts in marrow spaces near the suture (p < .04) than the normal sutures. Quantitative analysis of the normal sutures revealed that calvarial thickness was greater with age and that there was an inverse correlation between medullary area and age. For the affected sutures, there was also an age-related increase in calvarial thickness. There were also trends for age-related declines in numbers of osteoclasts in both open and affected sides.

Conclusions

These results question the hypothesis that defective osteoclastic activity is pivotal in the pathogenesis of UCS and support the hypothesis that this condition results from abnormally active bony remodeling.

Models of cranial suture biology

Craniosynostosis is a common congenital defect caused by premature fusion of cranial sutures. The severe morphologic abnormalities and cognitive deficits resulting from craniosynostosis and the potential morbidity of surgical correction espouse the need for a deeper understanding of the complex etiology for this condition. Work in animal models for the past 20 years has been pivotal in advancing our understanding of normal suture biology and elucidating pathologic disease mechanisms. This article provides an overview of milestone studies in suture development, embryonic origins, and signaling mechanisms from an array of animal models including transgenic mice, rats, rabbits, fetal sheep, zebrafish, and frogs. This work contributes to an ongoing effort toward continued development of novel treatment strategies.

In utero surgery--current state of the art--part II

Background

Fetal surgery, also referred to as in utero, prenatal or intrauterine surgery, consists of treatment of congenital malformations during the fetal period. The idea of treating malformations diagnosed in the course of intrauterine life dates back to 1963, when Lilly performed the first blood transfusion in a fetus. Since then it has been introduced as a treatment option in a series of lethal malformations. Efforts are being made to treat nonlethal malformations by means of fetal surgery.

Material/Methods

A comprehensive search of the literature using MEDLINE and PubMed between 1925 and February 2009 was performed. Search terms for MEDLINE and PubMed were: fetal surgery, foetal surgery, in utero surgery, prenatal surgery, and in utero treatment. In addition, information was obtained at Web sites of the International Medicine and Surgery Society and the University of California Fetal Treatment Centre.

Results

Authors’ attention focused on the survey of indications to intrauterine operations. We outline potential directions of its development, quoting the groundwork of the most experienced researchers and clinicians. Moreover, owing to the authors’ interest in plastic surgery, some remarks on the role of intrauterine medicine and surgery in this branch of medicine are made.

Conclusions

In utero surgery may be regarded as an efficient tool of preventive medicine. It offers some advantages that no other branch of medicine may offer. However, its implementation is more troublesome than in the past, therefore only selected cases may benefit from its advantages. Nevertheless, current tendencies are to include, after thorough evaluation of benefit-risk ratio, some new indications for fetal surgery.

Force-induced craniosynostosis in the murine sagittal suture

BACKGROUND

The cause of nonsyndromic craniosynostosis remains elusive. Although compressive forces have been implicated in premature suture fusion, conclusive evidence of force-induced craniosynostosis is lacking. The purpose of this study was to determine whether cyclical loading of the murine calvaria could induce suture fusion.

METHODS

Calvarial coupons from postnatal day-21, B6CBA, wild-type mice (n = 18) were harvested and cultured. A custom appliance capable of delivering controlled, cyclical, compressive loads was applied perpendicular to the sagittal suture within the coupon in vitro. Nine coupons were subjected to 0.3 g of force for 30 minutes each day for a total of 14 days. A control group of nine coupons was clamped in the appliance without loading. Analysis of suture phenotype was performed using alkaline phosphatase and hematoxylin and eosin staining techniques and in situ hybridization analysis using bone sialoprotein.

RESULTS

Control group sagittal sutures-which normally remain patent in mice-showed their customary histologic appearance. In contradistinction, sagittal sutures subjected to cyclic loading showed histologic evidence of premature fusion (craniosynostosis). In addition, alkaline phosphatase activity and bone sialoprotein expression were observed to be increased in the experimental group when compared with matched controls.

CONCLUSIONS

An in vitro model of force-induced craniosynostosis has been devised. Premature fusion of the murine sagittal suture was induced with the application of controlled, cyclical, compressive loads. These results implicate abnormal forces in the development of nonsyndromic craniosynostosis, which supports our global hypothesis that epigenetic phenomena play a crucial role in the pathogenesis of craniosynostosis.

Induced premaxillary suture fusion: class III malocclusion model

The etiology of class III malocclusion remains unknown. The present study investigates the relationship between craniofacial morphology and premaxillary suture fusion to test the hypothesis that class III malocclusion may be related to premaxillary suture fusion. Cyanoacrylate was applied to immobilize the left premaxillary suture in the experimental group. Sham surgeries in rats were used for controls. Dental impressions and radiographs were taken before and after surgery for comparison of craniofacial differences between groups. Overall cranial base lengths, craniofacial widths, and craniofacial angulations related to the anterior base showed significant differences between groups. At the end of the experiment, the growth of the snout in the experimental group was inhibited and deviated to the treated side, while no obvious change was seen in the control group. The results show that induced premaxillary suture fusion can affect craniofacial morphology and indicate that premature premaxillary suture fusion may result in class III malocclusion.

Effects of induced premaxillary suture fusion on the craniofacial morphology in growing rats

OBJECTIVE

Due to premaxillary rapid development and fusion with the maxilla at the fetus stage, the functions of the premaxillary suture still remain unclear. This study was designed to explore the effect of artificial induced premaxillary suture fusion on craniofacial morphology.

METHODS

Thirty Sprague Dawley rats were divided into control and experimental groups, with 3 week, 5 week and 8 week subgroups of five animals each. An incision was made in each rat along the premaxillary suture and cyanoacrylate was administered to immobilize the exposed premaxillary suture for experimental rats. No glue was applied to controls. Weights, dental impressions and radiographs were taken before and after surgery until sacrifice and used to determine the differences between groups using the one-way ANOVA test.

RESULTS

After immobilizing the premaxillary suture, significant changes in the craniofacial morphology were measured at the different time points. In the experimental groups, local changes occurred at the 3rd week. A global alteration in craniofacial morphology was apparent at the 8th week in the experimental group compared to the control. At each successive time point, craniofacial morphological alterations increased in rats with fused premaxillary sutures.

CONCLUSIONS

Induced premaxillary suture fusion can inhibit the growth of the premaxilla and cause extensive craniofacial morphological changes. These findings suggest that premaxillary suture fusion may be related to craniofacial malformation or malocclusion and to the formation of the flattened craniofacial profile in humans.

Intrauterine autogenous foetal bone transplantation for the repair of cleft-like defects in the mid-gestational sheep model

AIM

The success of intrauterine surgery in treating non-life-threatening malformations such as myelomeningocoele, has also renewed strong interest in using this technique for treating craniofacial malformations. Nevertheless, the only experimental cleft-like defect models known, are those concerning wound healing of soft tissues.

MATERIAL AND METHODS

Attempts were made to repair artificial cleft-like defects including transplantation of 11 autogenous foetal bone grafts from the iliac crest or ulna, and were randomly assigned to three study groups, using the mid-gestational sheep model. In a 4th study group, lyophilized collagen, a bone-regenerating bioresorbable implant material, was used to fill the alveolar defect.

RESULTS

In all groups, there was a slight degree of asymmetry and thinning of the lip. Radiological studies demonstrated a variable degree of abnormality of the maxilla, ranging from none to a mild deviation. Three-dimensional computer tomography, two-dimensional maximal intensity projection findings, and histological analysis confirmed bony healing of the alveolar cleft-like defect.

DISCUSSION/CONCLUSION

Intrauterine autogenous foetal bone transplantation for the repair of cleft-like defects in the sheep is feasible. This is a reliable and valuable model toward a possible clinical application for intrauterine treatment of clefts.

Unicoronal Suture Immobilization in the Fetal Rabbit

Pre-clinical evaluation of surgical procedures aimed to correct craniosynostosis is ideally performed in species of small animals characterized by perinatal brain development, early skeletal maturation, and genuine synostosis in all newborns. It would be nearly impossible to breed such a colony to homozygosity, so most researchers have resorted to artificial postnatal suture immobilization. Our aim was to test the hypothesis that artificial immobilization of a unicoronal suture in the fetal rabbit (25 days of gestation) would result in neurocranial growth alterations similar to those seen in the 9-day postnatally immobilized or congenital synostotic rabbit models. The advantages of prenatal immobilization are that rabbits can undergo the tested corrective procedure at postnatal day 9. This age corresponds to a human age of 6 months and allows the deformity and the effects of its correction to be more readily detected. The heads of 25-day-old fetuses of five time-dated pregnant New Zealand white rabbits were exposed by hysterotomy. The left unicoronal suture of 4 fetuses in each litter was immobilized with a polyglactin suture piercing the frontal and parietal bone plates. The remaining two fetuses were sham-operated. Nine days after spontaneous delivery, all rabbits were marked with four titanium screws close to the sagittal and coronal sutures. Growth was recorded with dorsoventral cephalograms at 9 and 90 days. The group with the immobilized suture showed a small increase in growth across the sagittal sutures. However, the decreases in growth at the unicoronal suture in both the immobilized (5.41-mm difference with sham-treated group) and nonimmobilized (1.17-mm difference with sham-treated group) were significant. Fetal immobilization results in growth alterations similar to those observed after postnatal immobilization.

Advances in Craniosynostosis Research and Management

The purpose of the present paper is to analyze the most recent advances in the field of craniosynostosis basic and clinical research and management, and to give an overview of the more frequently adopted surgical strategies. After reviewing some basic concepts regarding normal craniofacial embryology and growth, aetiopathogenesis of craniosynostosis and craniofacial dysostosis, classification and diagnosis and historical evolution of surgical treatment, the authors elaborate on a selection of topics that have modified our current understanding of and therapeutical approach to these disease processes. Areas covered include advances in molecular biology and genetics, imaging techniques and surgical planning, resorbable fixation technology, bone substitutes and tissue engineering, distraction osteogenesis and the spring-mediated cranioplasties, resorbable distractor devices, minimally invasive surgery and in utero surgery. A review of the main subtypes of craniosynostosis and craniofacial dysostosis is presented, including their specific clinical features and a commentary on the presently available surgical options.

Gene therapy in plastic surgery

Recent developments in gene therapy have shown promise in the treatment of soft-tissue repair, bone formation, nerve regeneration, and cranial suture development. This special topic article reviews commonly used methods of gene therapy and discusses their various advantages and disadvantages. In addition, an overview of new developments in gene therapy as they relate to plastic surgery is provided.

Plasticity of the endocranial base in nonsyndromic craniosynostosis

Limited in vivo data exist on the dysmorphology of the cranial base in nonsyndromic craniosynostosis. Few studies have documented the effect of calvarial surgery for synostosis on endocranial morphology. Previous work has suggested that the dysmorphology of the endocranial base is diagnostically specific for metopic, sagittal, and unicoronal sutures. The purpose of this study was to further evaluate the endocranial base in infants with nonsyndromic craniosynostosis by testing the hypothesis that the dysmorphology is, to some degree, a secondary deformation rather than a primary malformation. Three questions were addressed: (1) Can individuals reliably identify affected suture-specific endocranial-base morphology using standard templates? (2) Does calvarial surgery in infancy for craniosynostosis affect the perception of endocranial-base morphology? and (3) Does calvarial surgery in infancy for nonsyndromic craniosynostosis normalize the endocranial base?In this study, three-dimensional volumetric reconstructions from archived computed tomography digital data were processed using the ANALYZE imaging software. Dysmorphology was assessed by nine independent, blinded skilled observers who reviewed two separate sets of images of endocranial bases. Both sets contained images from the same patients: one set contained preoperative images, and the other contained images of the endocranial base 1 year after calvarial surgery. Observers were asked to sort each set into four suture-specific diagnostic groups: normal, unicoronal, metopic, and sagittal. Each set contained 10 patients with unicoronal synostosis, 10 with metopic synostosis, 10 with sagittal synostosis, and four normal patients. Seventy-eight percent of the total number of preoperative images were correctly sorted into the suture-specific diagnostic group, whereas only 55 percent of the total number of postoperative images were correctly matched. With regard to the individual sutures, the results were as follows (data are presented as preoperative accuracy versus postoperative accuracy): metopic, 76 percent versus 44 percent; sagittal, 58 percent versus 34 percent; unicoronal, 100 percent versus 79 percent; and normal, 83 percent versus 72 percent. Although 36 of 306 total images per group (12 percent) actually represented normal patients, the observers called 72 of 306 normal (24 percent) in the preoperative set versus 110 of 306 normal (36 percent) in the postoperative set. In conclusion, (1) the endocranial dysmorphology of nonsyndromic craniosynostosis is recognizably specific to the affected suture; (2) calvarial surgery for nonsyndromic craniosynostosis normalizes the endocranial base qualitatively with regard to the diminished ability of raters to identify the primary pathology; and (3) the documented postoperative changes in endocranial base morphology after calvarial surgery for nonsyndromic craniosynostosis in infancy indicates that a major component of that dysmorphology is a secondary deformity rather than a primary malformation.

Growth restriction of cranial sutures in the fetal lamb causes deformational changes, not craniosynostosis

Newborns with in utero cranial vault molding can present with severe forms of plagiocephaly. Intrauterine constraint has been proposed as one cause for craniosynostosis. The purpose of this experiment was to investigate whether rigid plate fixation across a fetal cranial suture, representing a severe form of growth restriction in utero, would lead to cranial suture fusion in a fetal lamb model. Six fetal lambs at 85 to 95 days gestation (term = 145 days) underwent laparotomy, hysterotomy, fetal coronal scalp incision, and miniplate screw fixation across the right coronal suture in utero. Two unoperated twins and four unoperated age-matched lambs were used as controls (n = 12). Animals were killed at both 4 and 8 weeks postoperatively. Fetal head analysis consisted of gross examination, photography, basilar and lateral radiographs, and three-dimensional computed tomographic scans. Cranial suture analysis consisted of imaging by computed tomographic scan (axial and sagittal cuts) and histology of experimentally plated coronal sutures, contralateral nonplated coronal sutures and twin control coronal sutures. Gross examination, radiographs, and three-dimensional computed tomographic analysis of heads with cranial suture plating showed ipsilateral forehead flattening, contralateral forehead bossing, superiorly displaced ipsilateral orbital rim, anterolateral projection of ipsilateral malar eminence, and anterior position of the ipsilateral ear point compared with the contralateral side of the same animal and normal controls. There was no change in nasal root, chin point, or predentition occlusal plane. Although analysis of the plated coronal sutures by computed tomographic scans showed diminished width or even stenosis, the histology revealed narrowed but patent experimental coronal sutures at 4 and 8 weeks. Contralateral, nonplated coronal sutures were not only patent, but widened compared with normal control sutures. This finding may have represented compensatory changes in the contralateral coronal suture caused by growth restriction at the plated suture. These data demonstrate that intrauterine growth restriction across a cranial suture caused by compression plate fixation resulted in deformational skull changes, not craniosynostosis. In addition, these data strongly support a role for in utero positional molding secondary to growth restriction in the maternal pelvis as a cause for nonsynostotic plagiocephaly seen in newborns.

New developments in craniofacial surgery research

The recent explosion in our understanding of developmental biology and genetics has enhanced our understanding of craniofacial biology. While it is not possible to summarize all new developments in craniofacial research, this article will review three areas: fetal models and surgery for craniofacial disorders, the biology of distraction osteogenesis, and the molecular mechanisms of cranial suture fusion. Numerous models of craniofacial disorders have been described, including small, short gestation and large, long gestation. The benefits and shortcomings of each are discussed. In addition, we discuss recent studies investigating the molecular mechanisms of mandibular distraction osteogenesis. Finally, we present a review of recent advances in the understanding of mechanisms of craniosynostosis, with particular emphasis on the biology of programmed cranial suture fusion in rodents.