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

Changes in Ventricular Volume After Posterior Vault Distraction Osteogenesis in Patients With Syndromic and Nonsyndromic Craniosynostosis

OBJECTIVE

Little is known about the response of the ventricular system to cranial vault surgery in patients with craniosynostosis. This study aims to evaluate the changes in the cerebral ventricular system in response to posterior vault distraction osteogenesis (PVDO) in patients with syndromic and nonsyndromic craniosynostosis.

METHODS

A single-institution retrospective review of all patients with craniosynostosis undergoing PVDO from 2000 to 2022 was completed. Patients were included for analysis if they had pre and postoperative cranial computed tomography scans. Ventricular volume (VV) and intracranial volume (ICV) were calculated using segmentation software.

RESULTS

Both patients with syndromic synostosis and nonsyndromic synostosis (NSS) experienced a significant increase in ICV after PVDO, but only patients with NSS experienced a significant VV change (P = 0.004). After normalization by ICV, total, lateral, and third VV changes retained significance with percentage increases of 114%, 117%, and 89%, respectively (P < 0.05 for all).

CONCLUSION

The differing results between cohorts reinforce the concept that the intracranial milieu is different between patients with syndromic synostosis and NSS. The results of the NSS cohort suggest that these patients may exist in a compensated state in which a reduction in cerebral blood flow and VV allows for the maintenance of parenchymal health to prevent the development of intracranial hypertension. Further studies may explore VV as a surrogate marker of ICP elevation, and the utility of cranial vault remodeling on nonsynostotic pathologies with cephalocranial disproportion.

Unravelling the pathogenesis of foramen magnum stenosis in patients with severe achondroplasia: a CT-based comparison with age-matched controls and FGFR3 craniosynostosis syndromes

OBJECTIVE

Foramen magnum(FM) stenosis can be responsible for acute and chronic damage to the cervicomedullary junction in children with achondroplasia. The bony anatomy and patterns of suture fusion of the FM in this context are incompletely understood, yet becoming increasingly important in the light of novel medical therapies for achondroplasia. The objective of this study was to describe and quantify bony anatomy and fusion patterns of FM stenosis in patients with achondroplasia using CT scans, comparing them to age-matched controls and other FGFR3 craniosynostosis patients.

METHODS

Patients with achondroplasia and severe FM stenosis, classified as achondroplasia foramen magnum score(AFMS) grades 3 and 4, were identified from a departmental operative database. All had pre-operative CT scans of the craniocervical junction. Measurements obtained comprised sagittal diameter (SD), transverse diameter (TD), foramen magnum area, and opisthion thickness. Anterior and posterior interoccipital synchondroses (AIOS and PIOS) were graded by the extent of fusion. These measurements were then compared with CT scans from 3 age-matched groups: the normal control group, children with Muenke syndrome, and children with Crouzon syndrome with acanthosis nigricans (CSAN).

RESULTS

CT scans were reviewed in 23 cases of patients with achondroplasia, 23 normal controls, 20 Muenke, and 15 CSAN. Children with achondroplasia had significantly smaller sagittal diameter (mean 16.2 ± 2.4 mm) compared to other groups (control 31.7 ± 2.4 mm, p < 0.0001; Muenke 31.7 ± 3.5 mm, p < 0.0001; and CSAN 23.1 ± 3.4 mm, p < 0.0001) and transverse diameters (mean 14.3 ± 1.8 mm) compared with other groups (control 26.5 ± 3.2 mm, p < 0.0001; Muenke 24.1 ± 2.6 mm, p < 0.0001; CSAN 19.1 ± 2.6 mm, p < 0.0001). This translated into a surface area which was 3.4 times smaller in the achondroplasia group compared with the control group. The median grade of the AIOS fusion achondroplasia group was 3.0 (IQR 3.0-5.0), which was significantly higher compared with the control group (1.0, IQR 1.0-1.0, p < 0.0001), Muenke group (1.0, IQR 1.0-1.0, p < 0.0001), and CSAN (2.0, IQR 1.0-2.0, p < 0.0002). Median PIOS fusion grade was also highest in the achondroplasia group (5.0, IQR 4.0-5.0) compared with control (1.0, IQR 1.0-1.0, p < 0.0001), Muenke (2.5, IQR 1.3-3.0, p < 0.0001), and CSAN (4.0, IQR 4.0-4.0, p = 0.2). Distinct bony opisthion spurs projecting into the foramen magnum were seen in achondroplasia patients but not others, resulting in characteristic crescent and cloverleaf shapes.

CONCLUSION

Patients with AFMS stages 3 and 4 have significantly reduced FM diameters, with surface area 3.4 times smaller than age-matched controls. This is associated with premature fusion of the AIOS and PIOS in comparison with controls and other FGFR3-related conditions. The presence of thickened opisthion bony spurs contributes to stenosis in achondroplasia. Understanding and quantifying bony changes at the FM of patients with achondroplasia will be important in the future quantitative evaluation of emerging medical therapies.

Chiari I malformation: management evolution and technical innovation

BACKGROUND AND DEFINITION

In recent years thanks to the growing use of radiological assessment, Chiari I malformation became one of the major diseases for a neurosurgeon to deal with. CIM can be classified according to the extent of cerebellar tonsil tip into the foramen magnum being a protrusion over five mm considered pathological. Such a disease is a heterogeneous condition with a multifactorial pathogenetic mechanism that can subdivided into a primary and secondary form. Regardless of the form, it seems that CIM is the result of an imbalance between the volume of the braincase and its content. Acquired CIMs are secondary to conditions causing intracranial hypertension or hypotension while the pathogenesis of primary forms is still controversial.

PATHOGENESIS AND TREATMENT

There are several theories in the literature but the most accepted one implies an overcrowding due to a small posterior cranial fossa. While asymptomatic CIM do not need treatment, symptomatic ones prompt for surgical management. Several techniques are proposed being the dilemma centered in the need for dural opening procedures and bony decompression ones.

CONCLUSION

Alongside the paper, the authors will address the novelty presented in the literature on management, diagnosis and pathogenesis in order to offer a better understanding of such a heterogeneous pathology.

Overexpression of fibroblast growth factor receptor 2 in bone marrow mesenchymal stem cells enhances osteogenesis and promotes critical cranial bone defect regeneration

Background: Reconstruction of cranial bone defects is one of the most challenging problems in reconstructive surgery, and several biological tissue engineering methods have been used to promote bone repair, such as genetic engineering of bone marrow mesenchymal stem cells (BMSCs). Fibroblast growth factor receptor 2 (Fgfr2) is an important regulator of bone construction and can be used as a potential gene editing site. However, its role in the osteogenesis process of BMSCs remains unclear. This article clarifies the function of Fgfr2 in BMSCs and explores the role of Fgfr2-overexpressed BMSCs carried by light-induced porous hydrogel (GelMA) in the repair of cranial bone defects. Methods: Lenti-virus was used to overexpress Fgfr2 in BMSCs, and cell counting kit-8, transwell, and flow cytometry assays were conducted to investigate the proliferation, migration, and characteristics. After 0, 3, 7, and 10 days of osteogenic or chondrogenic induction, the changes in osteogenic and chondrogenic ability were detected by real-time PCR, western blot, alkaline phosphatase staining, alizarin Red staining, and alcian blue staining. To investigate the viability of BMSCs carried by GelMA, calcein and propyl iodide staining were carried out as well. Finally, a critical cranial bone defect model was established in 6-week-old male mice and micro-computerized tomography, masson staining, and immunohistochemistry of OCN were conducted to test the bone regeneration properties of implanting Fgfr2-overexpressed BMSCs with GelMA in cranial bone defects over 6 weeks. Results: Overexpression of Fgfr2 in BMSCs significantly promoted cell proliferation and migration and increased the percentage of CD200+CD105+ cells. After osteogenic and chondrogenic induction, Fgfr2 overexpression enhanced both osteogenic and chondrogenic ability. Furthermore, in cranial bone defect regeneration, BMSCs carried by light-induced GelMA showed favorable biocompatibility, and Fgfr2-overexpressed BMSCs induced superior cranial bone regeneration compared to a normal BMSCs group and an untreated blank group. Conclusion: In vitro, Fgfr2 enhanced the proliferation, migration, and stemness of BMSCs and promoted osteogenesis and chondrogenesis after parallel induction. In vivo, BMSCs with Fgfr2 overexpression carried by GelMA showed favorable performance in treating critical cranial bone defects. This study clarifies the multiple functions of Fgfr2 in BMSCs and provides a new method for future tissue engineering.

Changes in venous drainage after posterior cranial vault distraction and foramen magnum decompression in syndromic craniosynostosis

OBJECTIVE

The authors' objective was to measure the effect of posterior cranial vault distraction (PCVD) plus foramen magnum decompression (FMD) on dural sinus volume and venous flow in patients with syndromic craniosynostosis.

METHODS

The volumes of the sagittal, straight, transverse, and sigmoid sinuses of 5 consecutive patients with syndromic craniosynostosis who underwent PCVD+FMD were calculated in cubic centimeters with T2-weighted volumetric MRI sequences before surgery, immediately after surgery, and after the end of the distraction process. Tridimensional reconstructions of phase-contrast magnetic resonance angiography (PC-MRA) images were obtained with multiplanar reconstruction (MPR).

RESULTS

The average total volume of all dural sinuses increased immediately after surgery (from 10.06 cm3 to 12.64 cm3) and continued to increase throughout the 30-day distraction period (from 12.64 cm3 to 14.71 cm3) (p = 0.04), except that the right sigmoid sinus remained stable after the initial increase. The most important increases were observed for the left transverse sinus (+113.2%), right transverse sinus (+104.3%), left sigmoid sinus (+91.3%), and sagittal sinus (+41.8%). Less important modifications were evident for the right sigmoid sinus (+33.7%) and straight sinus (+23.4%). Significant improvements in venous flow were noted on the tridimensional reconstructions of the PC-MRA images. Venous obstruction grading score improved in 4 patients (average [range] 2.4 [ 2-5]) (p = 0.023) and remained stable in 1 patient. All patients had chronic tonsillar herniation (CTH) (mean [range] 16.6 [8-26] mm), and 3 had syringomyelia. CTH showed improvement on the last follow-up MRI evaluation in 4 patients (mean [range] 10.5 [0-25] mm) and worsened from 15 mm to 19 mm in 1 patient. Syringomyelia improved in 2 patients and remained unchanged in 1.

CONCLUSIONS

This study has provided the first radiological evidence of the impact of craniofacial surgery on dural sinus anatomy and venous drainage. The venous anomalies described in patients with syndromic craniosynostosis are not static, and PCVD+FMD triggers a dynamic process that can lead to significant modifications of intracranial venous drainage. The traction exerted by the distracted bone flap onto the occipitoparietal dura mater adherent to the inner calvaria may account for the enlargement of the dural sinus throughout the distraction period. The impact of these modifications on venous pressure, intracranial pressure, CTH, and hydrocephalus remains to be determined.

Management of ventriculomegaly in pediatric patients with syndromic craniosynostosis: a single center experience

INTRODUCTION

Management of ventriculomegaly in pediatric patients with syndromic craniosynostosis (SC) requires understanding the underlying mechanisms that cause increased intracranial pressure (ICP) and the role of cerebrospinal fluid (CSF) in cranial vault expansion in order to select the best treatment option for each individual patient.

METHODS

A total of 33 pediatric patients with SC requiring craniofacial surgery were retrospectively evaluated. Cases of nonsyndromic craniosynostosis and shunt-induced craniosynostosis were excluded. Six syndrome-based categories were distinguished: Crouzon syndrome, Pfeiffer syndrome, Apert syndrome, cloverleaf skull syndrome, and others (Muenke syndrome, Sensenbrenner syndrome, unclassified). All of the patients were treated surgically for their cranial deformity between 2010 and 2016. The presence of ventriculomegaly and ventriculoperitoneal (VP) shunt requirement with its impact in cranial vault expansion were analyzed. Clinical and neuroimaging studies covering the time from presentation through the follow-up period were revised. The mean postoperative follow-up was 6 years and 3 months. A systematic review of the literature was conducted through a PubMed search.

RESULTS

Of the total of 33 patients with SC, 18 (54.5%) developed ventriculomegaly and 13 (39.4%) required ventriculoperitoneal (VP) shunt placement. Six patients (18.2%) required shunt placement previous to craniofacial surgery. Seven patients (21.2%) required a shunt after craniofacial surgery. Seven fixed pressure ventriculoperitoneal shunts and six programmable valves were placed as first choice. All patients improved their clinical symptoms after shunt placement. Aesthetic results seemed to be better in patients with programmable shunts.

CONCLUSIONS

Unless clear criteria for overt hydrocephalus are present, it is recommended to perform craniofacial surgery as a first step in the management of patients with SC in order to preserve the expansive effect of CSF for cranial vault expansion. In our experience, the use of externally programmable valves allows for the treatment of hydrocephalus while maintaining the expansive effect of CSF for the remodeling of the cranial vault. Prospective evaluations are needed to determine causality.

Craniosynostosis and hydrocephalus: relevance and treatment modalities

INTRODUCTION

Hydrocephalus is variously associated to syndromic craniosynostosis (CS), while it is randomly encountered in monosutural CS. Pathogenesis is still debated and reliable criteria for the diagnosis of overt hydrocephalus are lacking. Additionally, optimal treatment is controversial since it should balance the need to relieve intracranial hypertension and the risk of recurrence favored by lowering intracranial pressure.

METHODS

A thorough review of the literature has been performed. Accordingly, pathogenic theories, diagnostic issues, and treatment options on hydrocephalus presenting in the context of CS are discussed.

RESULTS

The association of hydrocephalus to simple CS is considered a fortuitous event. Its treatment is usually driven by the etiology and clinical relevance of hydrocephalus, favoring treatment before surgical correction to reduce CSF-related complications. On the other side, pathogenesis of hydrocephalus in the context of syndromic CS has been mainly related to factors that are secondary to the synostostic process, such as craniocerebral disproportion and venous hypertension. Hydrocephalus complicates 12-15% of syndromic CS, though its incidence is more relevant in FGFR2-related CS and raises up to 88% in Pfeiffer syndrome. Overt hydrocephalus should be properly differentiated by non-tense ventriculomegaly that is more frequent in Apert syndrome. Since intracranial hypertension is constant in syndromic CS even in the absence of active hydrocephalus, radiological monitoring of ventricular size along with intracranial pressure monitoring is essential. Active hydrocephalus occurs more frequently in infants, though stable ventriculomegaly may evolve into overt hydrocephalus after cranial expansion. If hydrocephalus is not clinically prominent, cranial expansion should be favored as first surgical step. Although posterior cranial expansion may address posterior cranial fossa constriction and stabilize ventricular dilation, effectiveness in long-term control of hydrocephalus is not clear. ETV is an effective treatment option, though success rate is affected by the presence of brain malformations and patient age. Extrathecal CSF shunting should be used as last resource due to the increased risk of complications in this context.

CONCLUSIONS

The pathogenesis of hydrocephalus complicating syndromic CS should be further investigated. Concomitantly, the definition of reliable diagnostic criteria is advocated in order to promptly and properly identify active hydrocephalus. Finally, treatment algorithm should refine the best timing and treatment options aiming to relieve intracranial hypertension on one side and reduce the risk of restenosis on the other side.

Crouzon syndrome: posterior fossa volume studies in vestibular orientation

INTRODUCTION

With the increasing possibilities of surgical treatment addressing the complex spectrum of defects in Crouzon syndrome (CS), it is of utmost importance to obtain accurate assessment of the malformation. Evaluating the volume of the posterior fossa is of great importance since many authors, considering that its volume is always decreased, favor posterior fossa enlargement as a first step in the treatment of CS.

MATERIAL AND METHODS

We studied CT scans of children with CS, which were vestibular-oriented (VO) in order to conform with physiological landmarks, and we measured intracranial volume by manual segmentation; these abnormal CT scans were superposed with VO 3D-CT scanners of age-matched controls. We studied the volume index of the posterior fossa for each CS patient defined as the ratio of its volume in CS patients with the normal for age calculated from normal controls.

RESULTS

We studied the imaging of 41 children with CS and 70 control. Among CS patients, the volume of the posterior fossa was increased in 10, compared with control. We found closure of the sphenoidal synchondrosis was correlated with age and with the width of the posterior fossa, but not with its length nor with the posterior fossa volume index.

CONCLUSION

Segmentation on VO-CT scanner and superposition with CT scanners of normal controls is a powerful tool for the study of the impact of CS or other synostoses on volume and shape. We found that CS is more heterogeneous than previously thought, and surgical strategies should be adapted accordingly.

Functional and morphological changes in hypoplasic posterior fossa

BACKGROUND

The knowledge of the development and the anatomy of the posterior cranial fossa (PCF) is crucial to define the occurrence and the prognosis of diseases where the surface and/or the volume of PCF is reduced, as several forms of craniosynostosis or Chiari type I malformation (CIM). To understand the functional and morphological changes resulting from such a hypoplasia is mandatory for their correct management. The purpose of this article is to review the pertinent literature to provide an update on this topic.

METHODS

The related and most recent literature addressing the issue of the changes in hypoplasic PCF has been reviewed with particular interest in the studies focusing on the PCF characteristics in craniosynostosis, CIM, and achondroplasia.

RESULTS AND CONCLUSIONS

In craniosynostoses, namely, the syndromic ones, PCF shows different degrees of hypoplasia, according to the different pattern and timing of early suture fusion. Several factors concur to PCF hypoplasia and contribute to the resulting problems (CIM, hydrocephalus), as the fusion of the major and minor sutures of the lambdoid arch, the involvement of the basal synchondroses, and the occlusion of the jugular foramina. The combination of these factors explains the variety of the clinical and radiological phenotypes. In primary CIM, the matter is complicated by the evidence that, in spite of impaired PCF 2D measurements and theories on the mesodermal defect, the PCF volumetry is often comparable to healthy subjects. CIM is revealed by the overcrowding of the foramen magnum that is the result of a cranio-cerebral disproportion (altered PCF brain volume/PCF total volume). Sometimes, this disproportion is evident and can be demonstrated (basilar invagination, real PCF hypoplasia); sometimes, it is not. Some recent genetic observations would suggest that CIM is the result of an excessive growth of the neural tissue rather than a reduced growth of PCF bones. Finally, in achondroplasia, both macrocephaly and reduced 2D and 3D values of PCF occur. Some aspects of this disease remain partially obscure, as the rare incidence of hydrocephalus and syringomyelia and the common occurrence of asymptomatic upper cervical spinal cord damage. On the other hand, the low rate of CIM could be explained on the basis of the reduced area of the foramen magnum, which would prevent the hindbrain herniation.