Correlation between head shape and volumetric changes following spring-assisted posterior vault expansion.

The aim of the study was to investigate whether different head shapes show different volumetric changes following spring-assisted posterior vault expansion (SA-PVE) and to investigate the influence of surgical and morphological parameters on SA-PVE. Preoperative three-dimensional skull models from patients who underwent SA-PVE were extracted from computed tomography scans. Patient head shape was described using statistical shape modelling (SSM) and principal component analysis (PCA). Preoperative and postoperative intracranial volume (ICV) and cranial index (CI) were calculated. Surgical and morphological parameters included skull bone thickness, number of springs, duration of spring insertion and type of osteotomy. In the analysis, 31 patients were included. SA-PVE resulted in a significant ICV increase (284.1 ± 171.6 cm3, p < 0.001) and a significant CI decrease (-2.9 ± 4.3%, p < 0.001). The first principal component was significantly correlated with change in ICV (Spearman ρ = 0.68, p < 0.001). Change in ICV was significantly correlated with skull bone thickness (ρ = -0.60, p < 0.001) and age at time of surgery (ρ = -0.60, p < 0.001). No correlations were found between the change in ICV and number of springs, duration of spring insertion and type of osteotomy. SA-PVE is effective for increasing the ICV and resolving raised intracranial pressure. Younger, brachycephalic patients benefit more from surgery in terms of ICV increase. Skull bone thickness seems to be a crucial factor and should be assessed to achieve optimal ICV increase. In contrast, insertion of more than two springs, duration of spring insertion or performing a fully cut through osteotomy do not seem to impact the ICV increase. When interpreting ICV increases, normal calvarial growth should be taken into account.

Spring-assisted posterior vault expansion-a single-centre experience of 200 cases.

PURPOSE: Children affected by premature fusion of the cranial sutures due to craniosynostosis can present with raised intracranial pressure and (turri)brachycephalic head shapes that require surgical treatment. Spring-assisted posterior vault expansion (SA-PVE) is the surgical technique of choice at Great Ormond Street Hospital for Children (GOSH), London, UK. This study aims to report the SA-PVE clinical experience of GOSH to date. METHODS: A retrospective review was carried out including all SA-PVE cases performed at GOSH between 2008 and 2020. Demographic and clinical data were recorded including genetic diagnosis, craniofacial surgical history, surgical indication and assessment, age at time of surgery (spring insertion and removal), operative time, in-patient stay, blood transfusion requirements, additional/secondary (cranio)facial procedures, and complications. RESULTS: Between 2008 and 2020, 200 SA-PVEs were undertaken in 184 patients (61% male). The study population consisted of patients affected by syndromic (65%) and non-syndromic disorders. Concerns regarding raised intracranial pressure were the surgical driver in 75% of the cases, with the remainder operated for shape correction. Median age for SA-PVE was 19 months (range, 2-131). Average operative time for first SA-PVE was 150 min and 87 for spring removal. Median in-patient stay was 3 nights, and 88 patients received a mean of 204.4 ml of blood transfusion at time of spring insertion. A single SA-PVE sufficed in 156 patients (85%) to date (26 springs still in situ at time of this analysis); 16 patients underwent repeat SA-PVE, whilst 12 underwent rigid redo. A second SA-PVE was needed in significantly more cases when the first SA-PVE was performed before age 1 year. Complications occurred in 26 patients with a total of 32 events, including one death. Forty-one patients underwent fronto-orbital remodelling at spring removal and 22 required additional cranio(maxillo)facial procedures. CONCLUSIONS: Spring-assisted posterior vault expansion is a safe, efficient, and effective procedure based on our 12-year experience. Those that are treated early in life might require a repeat SA-PVE. Long-term follow-up is recommended as some would require additional craniomaxillofacial correction later in life.

Local Soft Tissue and Bone Displacements Following Midfacial Bipartition Distraction in Apert Syndrome - Quantification Using a Semi-Automated Method.

ABSTRACT: Patients with Apert syndrome experience midfacial hypoplasia, hypertelorism, and downslanting palpebral fissures which can be corrected by midfacial bipartition distraction with rigid external distraction device. Quantitative studies typically focus on quantifying rigid advancement and rotation postdistraction, but intrinsic shape changes of bone and soft tissue remain unknown. This study presents a method to quantify these changes. Pre- and post-operative computed tomography scans from patients with Apert syndrome undergoing midfacial bipartition distraction with rigid external distraction device were collected. Digital Imaging and Communications in Medicine files were converted to three-dimensional bone and soft tissue reconstructions. Postoperative reconstructions were aligned on the preoperative maxilla, followed by nonrigid iterative closest point transformation to determine local shape changes. Anatomical point-to-point displacements were calculated and visualized using a heatmap and arrow map. Nine patients were included.Zygomatic arches and frontal bone demonstrated the largest changes. Mid-lateral to supra-orbital rim showed an upward, inward motion. Mean bone displacements ranged from 3.3 to 12.8 mm. Soft tissue displacements were relatively smaller, with greatest changes at the lateral canthi. Midfacial bipartition distraction with rigid external distraction device results in upward, inward rotation of the orbits, upward rotation of the zygomatic arch, and relative posterior motion of the frontal bone. Local movements were successfully quantified using a novel method, which can be applied to other surgical techniques/syndromes.

Statistical shape modelling for the analysis of head shape variations.

The aim of this study is, firstly, to create a population-based 3D head shape model for the 0 to 2-year-old subjects to describe head shape variability within a normal population and, secondly, to test a combined normal and sagittal craniosynostosis (SAG) population model, able to provide surgical outcome assessment. 3D head shapes of patients affected by non-cranial related pathologies and of SAG patients (pre- and post-op) were extracted either from head CTs or 3D stereophotography scans, and processed. Statistical shape modelling (SSM) was used to describe shape variability using two models - a normal population model (MODEL1) and a combined normal and SAG population model (MODEL2). Head shape variability was described via principal components analysis (PCA) which calculates shape modes describing specific shape features. MODEL1 (n = 65) mode 1 showed statistical correlation (p < 0.001) with width (125.8 ± 13.6 mm), length (151.3 ± 17.4 mm) and height (112.5 ± 11.1 mm) whilst mode 2 showed correlation with cranial index (83.5 mm ± 6.3 mm, p < 0.001). The remaining 9 modes showed more subtle head shape variability. MODEL2 (n = 159) revealed that post-operative head shape still did not achieve full shape normalization with either spring cranioplasty or total calvarial remodelling. This study proves that SSM has the potential to describe detailed anatomical variations in a paediatric population.

A machine learning framework for automated diagnosis and computer-assisted planning in plastic and reconstructive surgery.

Current computational tools for planning and simulation in plastic and reconstructive surgery lack sufficient precision and are time-consuming, thus resulting in limited adoption. Although computer-assisted surgical planning systems help to improve clinical outcomes, shorten operation time and reduce cost, they are often too complex and require extensive manual input, which ultimately limits their use in doctor-patient communication and clinical decision making. Here, we present the first large-scale clinical 3D morphable model, a machine-learning-based framework involving supervised learning for diagnostics, risk stratification, and treatment simulation. The model, trained and validated with 4,261 faces of healthy volunteers and orthognathic (jaw) surgery patients, diagnoses patients with 95.5% sensitivity and 95.2% specificity, and simulates surgical outcomes with a mean accuracy of 1.1 ± 0.3 mm. We demonstrate how this model could fully-automatically aid diagnosis and provide patient-specific treatment plans from a 3D scan alone, to help efficient clinical decision making and improve clinical understanding of face shape as a marker for primary and secondary surgery.

The turricephaly index: A validated method for recording turricephaly and its natural history in Apert syndrome.

INTRODUCTION: We present the CT scan-derived turricephaly index (TI) as a quotient of the maximal occipito-frontal length of the skull to the distance from the centre of the sella to the highest point on the vertex as a validated tool for assessing turricephaly and evaluating surgical techniques aimed at reducing it. MATERIALS AND METHODS: Measurements taken from CTs of non-operated children with Apert syndrome and age-matched controls were analysed using Centricity PACS system (from the lateral scout image) and the thick-sliced Osirix tool. CTs from non-operated children with Apert syndrome were used to investigate the natural history of their turricephaly both as a group and individually. RESULTS: There was statistically significant agreement between measurements taken from the CT scout and Osirix for 42 control children (R2 = 0.97) and 42 children with Apert syndrome (R2 = 0.98) and between two separate observers. There was a statistically significant difference (p < 0.001) between CT scout-derived TI value between controls (1.73 ± 0.12, range 1.46-1.99) and Apert children (1.42 ± 0.15, range 1.13-1.73). Analysis of 113 CTs of 65 non-operated children with Apert syndrome showed a decrease in turricephaly with age (positive spearman correlation: r = 0.50, p < 0.001). Analysis of 37 CTs of those with multiple (>2) CT's showed a similar decrease in turricephaly in the individual child (p < 0.001). CONCLUSIONS: TI derived from the CT scout view provides a simple, objective and validated method for assessing turricephaly. We recommend it for monitoring and for the prospective evaluation of reconstructive techniques in children with complex/syndromic craniosynostosis.

Using principal component analysis to describe the midfacial deformities in patients with craniofacial microsomia.

PURPOSE: Craniofacial microsomia (CFM) is the result of a disturbance in embryologic development and is characterised by an asymmetric, mostly unilateral facial underdevelopment. The aim of this study is to understand the midfacial involvement in CFM using principal component analysis (PCA). MATERIALS AND METHODS: Pre-operative data from 19 CFM and 23 control patients were collected. A set of 71 landmarks was placed on three-dimensional (3D) reconstructions of all skulls to compare both populations. PCA visualised variation within both groups and calculated the vector of change. Linear measurements were taken to compare ratios between the populations and between the affected and unaffected sides in CFM patients. RESULTS: PCA defined a vector that described shape changes between both populations. Videos showed the variation within the control and CFM group and the transformation from a mean CFM skull into a normal phenotype. Linear measurements showed a significant difference between the affected and unaffected sides in CFM patients. CONCLUSION: PCA has not been applied on asymmetrical data before, but it has proved to be a useful method to describe CFM. The virtual normalisation of a mean CFM skull enables visualisation of the bony shape changes, which is promising to delineate and to plan surgical correction and could be used as an outcome measure.

Intracranial Volume and Head Circumference in Children with Unoperated Syndromic Craniosynostosis.

BACKGROUND: When analyzing intracranial volume gain resulting from operative intervention in craniosynostosis, it is necessary to understand the underlying growth. The authors sought to create comprehensive intracranial volume and occipitofrontal circumference growth charts, as measured on unoperated craniosynostotic children, and aimed to investigate whether intracranial volume and occipitofrontal circumference could act as proxy measures for each other. METHODS: All preoperative Great Ormond Street Hospital patients with a diagnosis of Apert, Crouzon-Pfeiffer, or Saethre-Chotzen syndrome from the year 2004 onward were considered for this study. A control group of unaffected Great Ormond Street Hospital patients were also measured. Intracranial volume and occipitofrontal circumference were measured on the same scans. To study correlation between intracranial volume and occipitofrontal circumference, logarithmic fits were assessed. RESULTS: One hundred forty-seven craniosynostotic children with 221 preoperative scans were included (81 Apert, 81 Crouzon, 31 Pfeiffer, and 28 Saethre-Chotzen). The control group comprised 56 patients with 58 scans. Apert intracranial volume curves were significantly larger than those of other syndromes from 206 days onward; occipitofrontal circumference curves were not significantly different. The correlation coefficient between intracranial volume and occipitofrontal circumference was R = 0.87 for all syndromes combined and R = 0.91 for the control group. CONCLUSIONS: Apert syndrome children have a larger intracranial volume than children with other syndromic craniosynostotic conditions and unaffected children but maintain a similar occipitofrontal circumference. This study demonstrates high correlation between intracranial volume and occipitofrontal circumference with clinical care implications. The authors' reference growth curves can be used to monitor intracranial volume change over time and correct operative change for underlying growth.

A novel soft tissue prediction methodology for orthognathic surgery based on probabilistic finite element modelling.

Repositioning of the maxilla in orthognathic surgery is carried out for functional and aesthetic purposes. Pre-surgical planning tools can predict 3D facial appearance by computing the response of the soft tissue to the changes to the underlying skeleton. The clinical use of commercial prediction software remains controversial, likely due to the deterministic nature of these computational predictions. A novel probabilistic finite element model (FEM) for the prediction of postoperative facial soft tissues is proposed in this paper. A probabilistic FEM was developed and validated on a cohort of eight patients who underwent maxillary repositioning and had pre- and postoperative cone beam computed tomography (CBCT) scans taken. Firstly, a variables correlation assessed various modelling parameters. Secondly, a design of experiments (DOE) provided a range of potential outcomes based on uniformly distributed input parameters, followed by an optimisation. Lastly, the second DOE iteration provided optimised predictions with a probability range. A range of 3D predictions was obtained using the probabilistic FEM and validated using reconstructed soft tissue surfaces from the postoperative CBCT data. The predictions in the nose and upper lip areas accurately include the true postoperative position, whereas the prediction under-estimates the position of the cheeks and lower lip. A probabilistic FEM has been developed and validated for the prediction of the facial appearance following orthognathic surgery. This method shows how inaccuracies in the modelling and uncertainties in executing surgical planning influence the soft tissue prediction and it provides a range of predictions including a minimum and maximum, which may be helpful for patients in understanding the impact of surgery on the face.

Intracranial Volume Measurement: A Systematic Review and Comparison of Different Techniques.

The ability to calculate intracranial volume (ICV) from 3-dimensional imaging is a useful tool in a craniofacial team's armamentarium. Intracranial volume uses range from decision making to assessment. Various methods to calculate ICV exist including fully manual, semiautomatic, and fully automatic techniques and they are used with varying frequency in craniofacial centres globally.This study aimed to systematically analyze and compare ICV calculations across the 3 methods and provide information to allow the reader to utilize these processes in practice.Twenty-six computed tomography scans from Apert patients were used to compare ICV measurements calculated using the following techniques: fully manual segmentation with OsiriX (taken as the gold standard); semiautomatic segmentation using Simpleware ScanIP; and fully automatic segmentation using FSL neuroimaging software. In addition, to assess the effect that a reducing CT scan slice number had on ICV measurement, 13 scans were remeasured using half, quarter, and an eighth of the slices of the full scan.The manual and semiautomatic techniques had intraclass correlation coefficients of 0.997, and 0.993 respectively. Intracranial volume measurements using the semi- and fully automatic techniques showed high linear correlation with manual techniques (R = 0.993 and R = 0.995). The coefficients of determination for full scan versus half, quarter, and eighth scan were R = 0.98, 0.96, and 0.94 respectively.Similar ICV results can be obtained using manual, semiautomatic, or automatic techniques with decreasing amount of time required to perform each method. Command line code for the fully automatic method is provided.

Three-dimensional surface scanners compared with standard anthropometric measurements for head shape.

Three-dimensional (3D) surface imaging devices designed to capture and quantify craniofacial surface morphology are becoming more common in clinical environments. Such scanners overcome the limitations of two-dimensional photographs while avoiding the ionizing radiation of computed tomography. The purpose of this study was to compare standard anthropometric cranial measurements with measurements taken from images acquired with 3D surface scanners. Two 3D scanners of different cost were used to acquire head shape data from thirteen adult volunteers: M4D scan and Structure Sensor. Head circumference and cephalic index were measured directly on the patients as well as on 3D scans acquired with the two scanners. To compare head volume measurements with a gold standard, magnetic resonance imaging scans were used. Repeatability and accuracy of both devices were evaluated. Intra-rater repeatability for both scanners was excellent (intraclass correlation coefficients > 0.99, p < 0.001). Direct and digital measures of head circumference, cephalic index and head volume were strongly correlated (0.85 < r < 0.91, p < 0.001). Compared to direct measurements, accuracy was highest for M4D scan. Both 3D scanners provide reproducible data of head circumference, cephalic index and head volume and show a strong correlation with traditional measurements. However, care must be taken when using absolute values.

Spring-Assisted Cranioplasty for the Correction of Nonsyndromic Scaphocephaly: A Quantitative Analysis of 100 Consecutive Cases.

BACKGROUND: Spring-assisted cranioplasty has been proposed as an alternative to total calvarial remodeling for sagittal craniosynostosis. Advantages include its minimally invasive nature, and reduced morbidity and hospital stay. Potential drawbacks include the need for a second procedure for removal and the lack of published long-term follow-up. The authors present a single-institution experience of 100 consecutive cases using a novel spring design. METHODS: All patients treated at the authors' institution between April of 2010 and September of 2014 were evaluated retrospectively. Patients with isolated nonsyndromic sagittal craniosynostosis were included. Data were collected for operative time, anesthetic time, hospital stay, transfusion requirement, and complications in addition to cephalic index preoperatively and at 1 day, 3 weeks, and 6 months postoperatively. RESULTS: One hundred patients were included. Mean cephalic index was 68 preoperatively, 71 at day 1, and 72 at 3 weeks and 6 months postoperatively. Nine patients required transfusion. Two patients developed a cerebrospinal fluid leak requiring intervention. One patient required early removal of springs because of infection. One patient had a wound dehiscence over the spring and one patient sustained a venous infarct with hemiplegia. Five patients required further calvarial remodeling surgery. CONCLUSIONS: The authors' modified spring design and protocol represents an effective strategy in the management of single-suture sagittal craniosynostosis with reduced total operative time and blood loss compared with alternative treatment strategies. In patients referred within the first 6 months of birth, this technique has become the authors' procedure of choice. In a minority of cases, especially in the older age groups, further remodeling surgery is required. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

Comparison of three-dimensional scanner systems for craniomaxillofacial imaging.

Two-dimensional photographs are the standard for assessing craniofacial surgery clinical outcomes despite lacking three-dimensional (3D) depth and shape. Therefore, 3D scanners have been gaining popularity in various fields of plastic and reconstructive surgery, including craniomaxillofacial surgery. Head shapes of eight adult volunteers were acquired using four 3D scanners: 1.5T Avanto MRI, Siemens; 3dMDface System, 3dMD Inc.; M4D Scan, Rodin4D; and Structure Sensor, Occipital Inc. Accuracy was evaluated as percentage of data within a range of 2 mm from the 3DMDface System reconstruction, by surface-to-surface root mean square (RMS) distances, and with facial distance maps. Precision was determined by RMS. Relative to the 3dMDface System, accuracy was the highest for M4D Scan (90% within 2 mm; RMS of 0.71 mm ± 0.28 mm), followed by Avanto MRI (86%; 1.11 mm ± 0.33 mm) and Structure Sensor (80%; 1.33 mm ± 0.46). M4D Scan and Structure Sensor precision were 0.50 ± 0.04 mm and 0.51 ± 0.03 mm, respectively. Clinical and technical requirements govern scanner choice; however, 3dMDface System and M4D Scan provide high-quality results. It is foreseeable that compact, handheld systems will become more popular in the near future.

Quantifying the effect of corrective surgery for trigonocephaly: A non-invasive, non-ionizing method using three-dimensional handheld scanning and statistical shape modelling.

Trigonocephaly in patients with metopic synostosis is corrected by fronto-orbital remodelling (FOR). The aim of this study was to quantitatively assess aesthetic outcomes of FOR by capturing 3D forehead scans of metopic patients pre- and post-operatively and comparing them with controls. Ten single-suture metopic patients undergoing FOR and 15 age-matched non-craniosynostotic controls were recruited at Great Ormond Street Hospital for Children (UK). Scans were acquired with a three-dimensional (3D) handheld camera and post-processed combining 3D imaging software. 3D scans were first used for cephalometric measurements. Statistical shape modelling was then used to compute the 3D mean head shapes of the three groups (FOR pre-op, post-op and controls). Head shape variations were described via principal component analysis (PCA). Cephalometric measurements showed that FOR significantly increased the forehead volume and improved trigonocephaly. This improvement was supported visually by pre- and post-operative computed mean 3D shapes and numerically by PCA (p < 0.001). Compared with controls, post-operative scans showed flatter foreheads (p < 0.001). In conclusion, 3D scanning followed by 3D statistical shape modelling enabled the 3D comparison of forehead shapes of metopic patients and non-craniosynostotic controls, and demonstrated that the adopted FOR technique was successful in correcting bitemporal narrowing but overcorrected the rounding of the forehead.

A Mock Circulatory System Incorporating a Compliant 3D-Printed Anatomical Model to Investigate Pulmonary Hemodynamics.

A realistic mock circulatory system (MCS) could be a valuable in vitro testbed to study human circulatory hemodynamics. The objective of this study was to design a MCS replicating the pulmonary arterial circulation, incorporating an anatomically representative arterial model suitable for testing clinically relevant scenarios. A second objective of the study was to ensure the system's compatibility with magnetic resonance imaging (MRI) for additional measurements. A latex pulmonary arterial model with two generations of bifurcations was manufactured starting from a 3D-printed mold reconstructed from patient data. The model was incorporated into a MCS for in vitro hydrodynamic measurements. The setup was tested under physiological pulsatile flow conditions and results were evaluated using wave intensity analysis (WIA) to investigate waves traveling in the arterial system. Increased pulmonary vascular resistance (IPVR) was simulated as an example of one pathological scenario. Flow split between right and left pulmonary artery was found to be realistic (54 and 46%, respectively). No substantial difference in pressure waveform was observed throughout the various generations of bifurcations. Based on WIA, three main waves were identified in the main pulmonary artery (MPA), that is, forward compression wave, backward compression wave, and forward expansion wave. For IPVR, a rise in mean pressure was recorded in the MPA, within the clinical range of pulmonary arterial hypertension. The feasibility of using the MCS in the MRI scanner was demonstrated with the MCS running 2 h consecutively while acquiring preliminary MRI data. This study shows the development and verification of a pulmonary MCS, including an anatomically correct, compliant latex phantom. The setup can be useful to explore a wide range of hemodynamic questions, including the development of patient- and pathology-specific models, considering the ease and low cost of producing rapid prototyping molds, and the versatility of the setup for invasive and noninvasive (i.e., MRI) measurements.