Modeling the effect of brain growth on cranial bones using finite-element analysis and geometric morphometrics

A landmarking protocol for geometric morphometric analysis of squamate endocasts

Landmark-based geometric morphometrics is widely used to study the morphology of the endocast, or internal mold of the braincase, and the diversity associated with this structure across vertebrates. Landmarks, as the basic unit of such methods, are intended to be points of correspondence, selected depending on the question at hand, whose proper definition is essential to guarantee robustness and reproducibility of results. In this study, 20 landmarks are defined to provide a framework to analyze the morphological variability in squamate endocasts. Ten species representing a cross-section of the diversity of Squamata from both phylogenetic and ecological (i.e., habitat) perspectives were considered, to select landmarks replicable throughout the entire clade, regardless of the degree of neuroanatomical resolution of the endocast. To assess the precision, accuracy, and repeatability of these newly defined landmarks, both intraobserver and interobserver error were investigated. Estimates of measurement error show that most of the landmarks established here are highly replicable, and preliminary results suggest that they capture aspects of endocast shape related to both phylogenetic and ecologic signals. This study provides a basis for further examinations of squamate endocast disparity using landmark-based geometric morphometrics.

Paediatric skull growth models: A systematic review of applications to normal skulls and craniosynostoses

INTRODUCTION

Craniosynostoses affect 1/2000 births and their incidence is currently increasing. Without surgery, craniosynostosis can lead to neurological issues due to restrained brain growth and social stigma due to abnormal head shapes. Understanding growth patterns is essential to develop surgical planning approaches and predict short- and long-term post-operative results. Here we provide a systematic review of normal and pathological cranial vault growth models.

MATERIAL AND METHODS

The systematic review of the literature identified descriptive and comprehensive skull growth models with the following criteria: full text articles dedicated to the skull vault of children under 2 years of age, without focus on molecular and cellular mechanisms. Models were analysed based on initial geometry, numerical method, age determination method and validation process.

RESULTS

A total of 14 articles including 17 models was reviewed. Four descriptive models were assessed, including 3 models using statistical analyses and 1 based on deformational methods. Thirteen comprehensive models were assessed including 7 finite element models and 6 diffusion models. Results from the current literature showed that successful models combined analyses of cranial vault shape and suture bone formation.

DISCUSSION

Growth modelling is central when assessing craniofacial architecture in young patients and will be a key factor in the development of future customized treatment strategies. Recurrent technical difficulties were encountered by most authors when generalizing a specific craniosynostosis model to all types of craniosynostoses, when assessing the role of the brain and when attempting to relate the age with different stages of growth.

A study of 285 cases of cranial vault suture closure in Chinese adults

PURPOSE

To examine the presence and characteristics of cranial vault suture closure in Chinese adults and to explore whether craniosacral therapy (CST) manipulation is rational from the anatomical perspective.

METHODS

Anthropological non-metric observation and craniometry were used to study 285 dry skull specimens of Chinese adults.

RESULTS

A total of 91 specimens with closed extracranial sutures were observed, with an occurrence rate of 31.93%. Based on the mode of closure, there were 32 cases of single type closure, with sagittal suture closure predominating with 20 cases (21.98%); 59 cases of composite closure, with a partial closure of coronal suture + sagittal suture + lambdoid suture predominating with 26 cases (28.57%). In terms of the degree of closure, there were 13 cases (14.28%) of sagittal suture grade 0 closure and 78 cases (85.72%) of grade 1 - 4 closure; 34 cases (37.36%) of coronal suture grade 0 closure and 57 cases (62.64%) of grade 1 - 4 closure; 47 cases (51.65%) of lambdoid suture grade 0 closure and 44 cases (48.35%) of grade 1 - 4 closure. The segment and degree of coronal suture closure (46, 80.7%) and lambdoid suture (31, 70.45%) were mostly left-right symmetrical. The bone surfaces on either side of the cranial vault sutures are embedded in each other, forming a rough, complex and interlocking bone-suture-bone structure.

CONCLUSION

This study observed the closure of the cranial vault suture, summarized its characteristics, and explored the irrationality of the CST manipulation. The anatomical characteristics of the cranial suture dictate that manipulation cannot push the cranial suture at will.

Using Sensitivity Analysis to Develop a Validated Computational Model of Post-operative Calvarial Growth in Sagittal Craniosynostosis

Craniosynostosis is the premature fusion of one or more sutures across the calvaria, resulting in morphological and health complications that require invasive corrective surgery. Finite element (FE) method is a powerful tool that can aid with preoperative planning and post-operative predictions of craniosynostosis outcomes. However, input factors can influence the prediction of skull growth and the pressure on the growing brain using this approach. Therefore, the aim of this study was to carry out a series of sensitivity studies to understand the effect of various input parameters on predicting the skull morphology of a sagittal synostosis patient post-operatively. Preoperative CT images of a 4-month old patient were used to develop a 3D model of the skull, in which calvarial bones, sutures, cerebrospinal fluid (CSF), and brain were segmented. Calvarial reconstructive surgery was virtually modeled and two intracranial content scenarios labeled “CSF present” and “CSF absent,” were then developed. FE method was used to predict the calvarial morphology up to 76 months of age with intracranial volume-bone contact parameters being established across the models. Sensitivity tests with regards to the choice of material properties, methods of simulating bone formation and the rate of bone formation across the sutures were undertaken. Results were compared to the in vivo data from the same patient. Sensitivity tests to the choice of various material properties highlighted that the defined elastic modulus for the craniotomies appears to have the greatest influence on the predicted overall skull morphology. The bone formation modeling approach across the sutures/craniotomies had a considerable impact on the level of contact pressure across the brain with minimum impact on the overall predicated morphology of the skull. Including the effect of CSF (based on the approach adopted here) displayed only a slight reduction in brain pressure outcomes. The sensitivity tests performed in this study set the foundation for future comparative studies using FE method to compare outcomes of different reconstruction techniques for the management of craniosynostosis.