Review of quantitative outcome analysis of cranial morphology in craniosynostosis

CranioRate: An Image-Based, Deep-Phenotyping Analysis Toolset and Online Clinician Interface for Metopic Craniosynostosis

BACKGROUND

The diagnosis and management of metopic craniosynostosis involve subjective decision-making at the point of care. The purpose of this work was to describe a quantitative severity metric and point-of-care user interface to aid clinicians in the management of metopic craniosynostosis and to provide a platform for future research through deep phenotyping.

METHODS

Two machine-learning algorithms were developed that quantify the severity of craniosynostosis-a supervised model specific to metopic craniosynostosis [Metopic Severity Score (MSS)] and an unsupervised model used for cranial morphology in general [Cranial Morphology Deviation (CMD)]. Computed tomographic (CT) images from multiple institutions were compiled to establish the spectrum of severity, and a point-of-care tool was developed and validated.

RESULTS

Over the study period (2019 to 2021), 254 patients with metopic craniosynostosis and 92 control patients who underwent CT scanning between the ages of 6 and 18 months were included. CT scans were processed using an unsupervised machine-learning based dysmorphology quantification tool, CranioRate. The average MSS was 0.0 ± 1.0 for normal controls and 4.9 ± 2.3 ( P < 0.001) for those with metopic synostosis. The average CMD was 85.2 ± 19.2 for normal controls and 189.9 ± 43.4 ( P < 0.001) for those with metopic synostosis. A point-of-care user interface (craniorate.org) has processed 46 CT images from 10 institutions.

CONCLUSIONS

The resulting quantification of severity using MSS and CMD has shown an improved capacity, relative to conventional measures, to automatically classify normal controls versus patients with metopic synostosis. The authors have mathematically described, in an objective and quantifiable manner, the distribution of phenotypes in metopic craniosynostosis.

A New Measure of Posterior Morphology in Sagittal Craniosynostosis: The Occipital Bullet Index

INTRODUCTION

Sagittal craniosynostosis (SC) is associated with scaphocephaly, an elongated narrow head shape. Assessment of regional severity in the scaphocephalic head is limited by the use of serial computed tomographic (CT) imaging or complex computer programing. Three-dimensional measurements of cranial surface morphology provide a radiation-free alternative for assessing cranial shape. This study describes the creation of an occipital bulleting index (OBI), a novel tool using surface morphology to assess the regional severity in patients with SC.

METHODS

Surface imaging from CT scans or 3D photographs of 360 individuals with SC and 221 normocephalic individuals were compared to identify differences in morphology. Cartesian grids were created on each individual's surface mesh using equidistant axial and sagittal planes. Area under the curve (AUC) analyses were performed to identify trends in regional morphology and create measures capturing population differences.

RESULTS

The largest differences were located in the medial regions posteriorly. Using these population trends, a measure was created to maximize AUC. The OBI has an AUC of 0.72 with a sensitivity of 74% and a specificity of 61%. When the frontal bossing index is applied in tandem, the two have a sensitivity of 94.7% and a specificity of 93.1%. Correlation between the two scores in individuals with SC was found to be negligible with an intraclass correlation coefficient of 0.018. Severity was found to be independent of age under 24 months, sex, and imaging modality.

CONCLUSIONS

This index creates a tool for differentiating control head shapes from those with SC and has the potential to allow for objective evaluation of the regional severity, outcomes of different surgical techniques, and tracking shape changes in individuals over time, without the need for radiation.

Applications of 3D photography in craniofacial surgery

Three-dimensional (3D) photography is becoming more common in craniosynostosis practice and may be used for research, archiving, and as a planning tool. In this article, an overview of the uses of 3D photography will be given, including systems available and illustrations of how they can be used. Important innovations in 3D computer vision will also be discussed, including the potential role of statistical shape modeling and analysis as an outcomes tool with presentation of some results and a review of the literature on the topic. Potential future applications in diagnostics using machine learning will also be presented.

Three-Dimensional Treatment Outcomes of a Virtual Helmet Design Protocol for Sagittal Strip Craniectomy

BACKGROUND

The helmet worn after sagittal strip craniectomy must be customized to the surgical procedure and the patient's anatomy to achieve optimal outcomes. This study compares three-dimensional head shape outcomes obtained from a novel virtual helmet design and from a traditional helmet design.

METHODS

Twenty-four patients underwent extended sagittal strip craniectomy performed by a single surgeon and helmet management performed by a single orthotist. Eleven patients constitute the traditional helmet group, with helmet design based on laser scans. Thirteen patients constitute the virtual helmet group, with helmet design based on an overlay of a three-dimensional volume rendering of a low-radiation protocol computed tomographic scan and three-dimensional photograph. Cephalic index and vertical height were recorded from three-dimensional photographs. Three-dimensional whole-head composite images were generated to compare global head shape outcomes to those of age-matched controls.

RESULTS

There was no significant difference in mean cephalic index between the virtual helmet group (83.70 ± 2.33) and controls (83.53 ± 2.40). The differences in mean cephalic index between the traditional helmet group (81.07 ± 3.37) and controls and in mean vertical height were each significant (p < 0.05). Three-dimensional analysis demonstrated normal biparietal and vertical dimensions in the virtual helmet group compared to controls. The traditional helmet group exhibited narrower biparietal dimension and greater vertical dimension compared to controls.

CONCLUSIONS

Traditional and virtual helmet protocols improved mean cephalic index, but the virtual helmet group yielded more consistent and greater change in cephalic index. The virtual helmet design protocol yielded three-dimensional outcomes similar to those of age-matched controls. Traditional helmet design yielded a narrower biparietal dimension and greater vertical dimension to the cranial vault compared to the virtual helmet group and controls.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Three-dimensional surface scanning methods in osteology: A topographical and geometric morphometric comparison

Objectives

Three‐dimensional (3D) data collected by structured light scanners, photogrammetry, and computed tomography (CT) scans are increasingly combined in joint analyses, even though the scanning techniques and reconstruction software differ considerably. The aim of the present study was to compare the quality and accuracy of surface models and landmark data obtained from modern clinical CT scanning, 3D structured light scanner, photogrammetry, and MicroScribe digitizer.

Material and methods

We tested 13 different photogrammetric software tools and compared surface models obtained by different methods for four articulated human pelves in a topographical analysis. We also measured a set of 219 landmarks and semilandmarks twice on every surface as well as directly on the dry bones with a MicroScribe digitizer.

Results

Only one photogrammetric software package yielded surface models of the complete pelves that could be used for further analysis. Despite the complex pelvic anatomy, all three methods (CT scanning, 3D structured light scanning, photogrammetry) yielded similar surface representations with average deviations among the surface models between 100 and 200 μm. A geometric morphometric analysis of the measured landmarks showed that the different scanning methods yielded similar shape variables, but data acquisition via MicroScribe digitizer was most prone to error.

Discussion

We demonstrated that three‐dimensional models obtained by different methods can be combined in a single analysis. Photogrammetry proved to be a cheap, quick, and accurate method to generate 3D surface models at useful resolutions, but photogrammetry software packages differ enormously in quality.

Public Perception of a Normal Head Shape in Children With Sagittal Craniosynostosis

: A question that remains unanswered is at what level of surgical correction does the public perceive a head shape to be "normal" or "acceptable?" For most cases of non-syndromic asymptomatic craniosynostosis, the parents desire for surgical correction is to improve the cosmetic appearance of head shape. At the time of this writing, the intraoperative surgeons' perspective of what constitutes an acceptable head shape is the target for surgical correction. In introducing an improved objectively cosmetic goal, an appropriate outcome measure would be to assess what the general public considers a normal or acceptable head shape in children with craniosynostosis.

METHOD

Twenty-two unique images were presented via an online crowdsourcing survey of a severe case of non-syndromic sagittal craniosynosis gradually corrected to an age and gender matched normalized head shape. Participants were recruited via the Sick Kids Twitter account. Participants were invited to rate the head shapes as "normal" or "abnormal."

RESULTS

The 538 participants completed the online survey. Participants were able to reliably and consistently identify normal and abnormal head shapes with a Kappa Score >0.775. Furthermore, participants indicated that a correction of 70% is required in order for the cranial deformity to be regarded as "normal." This threshold closely reflects a normal Cranial Index, which is a widely used morphometric outcome in craniosynostosis.

CONCLUSION

Crowdsourcing provides an ideal method for capturing the general population's perspective on what constitutes a normal and acceptable head shape in children with sagittal craniosynostosis. Laypersons are able to reliably and consistently distinguish cranial deformities from a "normal" head shape. The public indicates a threshold correction of 70% in sagittal craniosynosis to regard it as a "normal" head shape.

Outcome Measures Reported in Published Clinical Research Studies in Craniosynostosis: A Systematic Review

CONTEXT

The fair comparison of treatment interventions for craniosynostosis across different studies is expected to be impaired by incomplete reporting and the use of inconsistent outcomes.

OBJECTIVE

This review assessed the outcomes currently reported in studies of craniosynostosis, and whether these outcomes are formally defined and prespecified in the study methods.

DATA SOURCES, SEARCH TERMS, AND STUDY SELECTION

Studies were sourced via an electronic, multi-database literature search for "craniosynostosis." All primary, interventional research studies published from 2011 to 2015 were reviewed.

DATA EXTRACTION

Two independent researchers assessed each study for inclusion and performed the data extraction. For each study, data were extracted on the individual outcomes reported, and whether these outcomes were defined and prespecified in the methods.

DATA SYNTHESIS AND RESULTS

Of 1027 studies screened, 240 were included and proceeded to data extraction. These studies included 18,365 patients.2192 separate outcomes were reported. Of these, 851 outcomes (38.8%) were clearly defined, 1394 (63.6%) were prespecified in the study methods."Clinical and functional" was the most commonly reported outcome theme (900 outcomes, 41.1%), and "patient-reported" outcomes the least (7 outcomes, 0.3%)."Duration of surgery" was the most commonly reported single outcome (reported 80 times). "Cranial index" was the most variably defined outcome (18 different definitions used).

CONCLUSION

The outcomes reported following treatment interventions for craniosynostosis are incompletely and variably defined. Improving definitions for these outcomes may aid comparison of different management strategies and improve craniosynostosis care. Suboptimal prespecification of these outcomes in the study methods implied that outcome reporting bias cannot be excluded.

Cranial growth in isolated sagittal craniosynostosis compared with normal growth in the first 6 months of age

Sagittal craniosynostosis (SCS), the most common type of premature perinatal cranial suture fusion, results in abnormal head shape that requires extensive surgery to correct. It is important to find objective and repeatable measures of severity and surgical outcome to examine the effect of timing and technique on different SCS surgeries. The purpose of this study was to develop statistical models of infant (0-6 months old) skull growth in both normative and SCS subjects (prior to surgery). Our goal was to apply these models to the assessment of differences between these two groups in overall post-natal growth patterns and sutural growth rates as a first step to develop methods for predictive models of surgical outcome. We identified 81 patients with isolated, non-syndromic SCS from Seattle Children's Craniofacial Center patient database who had a preoperative CT exam before the age of 6 months. As a control group, we identified 117 CT exams without any craniofacial abnormalities or bone fractures in the same age group. We first created population-level templates from the CT images of the SCS and normal groups. All CT images from both groups, as well as the canonical templates of both cohorts, were annotated with anatomical landmarks, which were used in a growth model that predicted the locations of these landmarks at a given age based on each population. Using the template images and the landmark positions predicted by the growth models, we created 3D meshes for each week of age up to 6 months for both populations. To analyze the growth patterns at the suture sites, we annotated both templates with additional semi-landmarks equally spaced along the metopic, coronal, sagittal and lambdoidal cranial sutures. By transferring these semi-landmarks to meshes produced from the growth model, we measured the displacement of the bone borders and suture closure rates. We found that the growth at the metopic and coronal sutures were more rapid in the SCS cohort than in the normal cohort. The antero-posterior displacement of the semi-landmarks also indicated a more rapid growth in the sagittal plane in the SCS model than in the normal model. Statistical templates and geometric morphometrics are promising tools for understanding the growth patterns in normal and synostotic populations and to produce objective and reproducible measurements of severity and outcome. Our study is the first of its kind to quantify the bone growth for the first 6 months of life in both normal and sagittal synostosis patients.

Physiologic closure time of the metopic suture in South Australian infants from 3D CT scans

Metopic synostosis is a craniofacial condition characterised by the premature fusion of the metopic suture. This early fusion restricts frontal bone growth [17] and has significant impacts on the developing infant during a critical phase of rapid growth and development [4]. Diagnosis of the condition is usually achieved by clinical assessment, followed by a three-dimensional computed tomography (3D CT) scan, verifying premature metopic suture fusion.

PURPOSE

This retrospective study aims to investigate the timing of metopic suture fusion in the developing infant in an Australian subpopulation.

METHODS

The study evaluates metopic suture fusion in 258 cranial 3D CT scans of children aged 0-24 months over a 5-year period (2011-2016), scanned at Women's and Children's Hospital.

RESULTS

The findings suggest that the age range over which physiologic metopic suture fusion occurs is larger than previously reported.

CONCLUSIONS

The approximate range for physiologic fusion was found to be 3-19 months and patients with fusion within this range can be considered normal. Complete suture fusion is expected by 19 months. Additionally, results indicate suture fusion prior to 3 months is abnormal and diagnostically indicative of metopic synostosis.

Single Suture Synostosis and Isolated Cleft Palate in Non-Apert Syndrome Patients

INTRODUCTION

Single suture craniosynostosis (SSC) and isolated cleft palate (ICP) in non-Apert syndrome patients rarely occur together. Management includes airway optimization, timing surgery appropriately, and assessing both cranial vault aesthetics and speech outcomes. The aim of this study was to compare treatment pathways and outcomes in patients with both conditions to standard treatment for these conditions in isolation.

METHODS

Patient hospital medical records were retrospectively reviewed for demographic data, timing of surgery, aesthetic outcome (using the Whitaker grading system for head shape), and speech outcome (from speech therapy records of general development and speech assessment).

RESULTS

Six patients with SSC and ICP were identified over an 18-year period. Cranial surgery was performed between 4 and 16 months and cleft surgery between 6 and 34 months of age in all cases. Documentation of cleft surgery and genetic testing was not available for 1 patient. One patient with hemi-palatal absence had an obturator inserted at 34 months. Two patients were found to have Fragile X and Emanuel syndrome, respectively.No increased perioperative airway risk was highlighted in any case. Four cases were designated Whitaker grade 1, 1 case was designated grade 2, and 1 case was not graded as no cranial surgery was performed. Half of the patients had general and speech developmental delay, while the other half demonstrated no signs of developmental delay.

DISCUSSION/CONCLUSION

Examination of 6 patients with SSC and ICP suggests the presence of both conditions does not adversely impact management or outcome for each condition, or increase perioperative risk.

Statistical shape modelling to aid surgical planning: associations between surgical parameters and head shapes following spring-assisted cranioplasty

PURPOSE

Spring-assisted cranioplasty is performed to correct the long and narrow head shape of children with sagittal synostosis. Such corrective surgery involves osteotomies and the placement of spring-like distractors, which gradually expand to widen the skull until removal about 4 months later. Due to its dynamic nature, associations between surgical parameters and post-operative 3D head shape features are difficult to comprehend. The current study aimed at applying population-based statistical shape modelling to gain insight into how the choice of surgical parameters such as craniotomy size and spring positioning affects post-surgical head shape.

METHODS

Twenty consecutive patients with sagittal synostosis who underwent spring-assisted cranioplasty at Great Ormond Street Hospital for Children (London, UK) were prospectively recruited. Using a nonparametric statistical modelling technique based on mathematical currents, a 3D head shape template was computed from surface head scans of sagittal patients after spring removal. Partial least squares (PLS) regression was employed to quantify and visualise trends of localised head shape changes associated with the surgical parameters recorded during spring insertion: anterior-posterior and lateral craniotomy dimensions, anterior spring position and distance between anterior and posterior springs.

RESULTS

Bivariate correlations between surgical parameters and corresponding PLS shape vectors demonstrated that anterior-posterior (Pearson's [Formula: see text]) and lateral craniotomy dimensions (Spearman's [Formula: see text]), as well as the position of the anterior spring ([Formula: see text]) and the distance between both springs ([Formula: see text]) on average had significant effects on head shapes at the time of spring removal. Such effects were visualised on 3D models.

CONCLUSIONS

Population-based analysis of 3D post-operative medical images via computational statistical modelling tools allowed for detection of novel associations between surgical parameters and head shape features achieved following spring-assisted cranioplasty. The techniques described here could be extended to other cranio-maxillofacial procedures in order to assess post-operative outcomes and ultimately facilitate surgical decision making.