Sexual dimorphism in shape and size of the neurocranium.

Sex identification is a primary step in forensic analysis of skeletal remains. The accuracy of sex estimation methods greatly depends on the sexual dimorphism manifested by the target anatomical region. The study aims to evaluate the sexual dimorphism in shape and size of the neurocranium and to compare the potential of shape and size of different cranial regions to classify correctly the male and female crania. The study was carried out on computed tomography images of 373 Bulgarian adults (161 males and 212 females). Three-dimensional coordinates of 32 landmarks were acquired. The landmarks were arranged in 4 configurations: neurocranium, frontal bone, parietotemporal region, and occipital bone. For each configuration, the presence of significant sex differences in shape and size was tested. Principal component analysis (PCA) was applied to explore the shape variation. The classification power of size and shape was tested using discriminant analysis and k-means clustering. The neurocranium shows significant sex differences in shape and size. The parietotemporal region is the most dimorphic neurocranial part in size and the frontal bone is the most differing one in shape. The size of the parietotemporal region and frontal bone classifies correctly more than 80% of the crania. The discrimination ability based on shape is rather low as the highest values of about 70% are obtained for the frontal and occipital bone. The PCA plots show large overlapping of the male and female crania. It can be inferred that the sex-specific size differences in the neurocranium are more important than the shape differences.

Machine learning approaches for sex estimation using cranial measurements.

The aim of the present study is to apply support vector machines (SVM) and artificial neural network (ANN) as sex classifiers and to generate useful classification models for sex estimation based on cranial measurements. Besides, the performance of the generated sub-symbolic machine learning models is compared with models developed through logistic regression (LR). The study was carried out on computed tomography images of 393 Bulgarian adults (169 males and 224 females). The three-dimensional coordinates of 47 landmarks were acquired and used for calculation of the cranial measurements. A total of 64 measurements (linear distances, angles, triangle areas and heights) and 22 indices were calculated. Two datasets were assembled including the linear measurements only and all measurements and index, respectively. An additional third dataset comprising all possible interlandmark distances between the landmarks was constructed. Two machine learning algorithms-SVM and ANN and a traditional statistical analysis LR-were applied to generate models for sex estimation. In addition, two advanced attribute selection techniques (Weka BestFirst and Weka GeneticSearch) were used. The classification accuracy of the models was evaluated by means of 10 × 10-fold cross-validation procedure. All three methods achieved accuracy results higher than 95%. The best accuracy (96.1 ± 0.5%) was obtained by SVM and it was statistically significantly higher than the best results achieved by ANN and LR. SVM and ANN reached higher accuracy by training on the full datasets than the selection datasets, except for the sample described by the interlandmark distances, where the reduction of attributes by the GeneticSearch algorithm improved the accuracy.

Sagittal suture maturation: Morphological reorganization, relation to aging, and reliability as an age-at-death indicator.

OBJECTIVES: The sagittal suture (SS) is assumed to be an initial site for the commencement of cranial suture closure as well as the most frequent spot of isolated craniosynostosis. The present study aimed to inspect the reorganization of the SS at the microlevel to assess the relation between its closure and aging and to establish whether it could be used as a reliable indicator in age-at-death prediction. MATERIALS AND METHODS: The SS was investigated in 68 dry contemporary adult male skulls of known age-at-death. An additional series of 20 skulls was used for verification. The skulls were scanned using a micro-computed tomography system. The SS closure degree was assessed along the three bone layers on cross-sectional tomograms by using a scoring scale. RESULTS: In the entirely open SS, the bone edges consist of compact bone and are widely separated. With SS maturation, the bone edges come into contact, and the remodeling process leads to a decrease in the sutural area and bone homogenization across all three layers. SS closure is an irregular process roughly related to aging, beginning in the early 20s, reaching its peak at about 30 years of age and abating in the late 40s. DISCUSSION: Although related to aging, SS closure is not a simple function of it. Rather, the underlying factors inducing and managing this process are multifaceted and complex. Although the etiology of SS maturation remains unclear, it is reasonable to use SS closure cautiously and only as a supportive method for age prediction.

Digital radiomorphometric analysis of the frontal sinus and assessment of the relation between persistent metopic suture and frontal sinus development.

OBJECTIVES: This study aimed to establish the frequency of the frontal sinus (FS) aplasia, to compare metopic and nonmetopic series and thus to assess the relationship between the preservation of metopic suture and FS development. MATERIALS AND METHODS: FSs were investigated in 230 dry skulls of adult males distributed into control (137) and metopic (93) series. They were visualized through industrial digital radiography. RESULTS: In the control series, the FS aplasia was observed in 12.41% of the skulls, and it was mostly unilateral (8.76%) than bilateral (3.65%). The left-sided aplasia (5.11%) slightly prevailed over the right-sided one (3.65%). In the metopic series, the aplasia was observed with a frequency of 19.35%, and the bilateral aplasia (7.53%) was rarer that the unilateral one (11.83%), while the right-sided aplasia was clearly predominant (9.68%) compared to the left-sided one (2.15%). DISCUSSION: The significant differences between both series showed a tendency for the persistence of metopic suture to be frequently related with FS underdevelopment in the vertical plate of the frontal bone, but in cases of pneumatization, it was preferentially on the left side. Taking into account that the cranial hypertension leads to suture diastasis and hinders development of the FS, it could be suggested that persistence of the metopic suture along with underdevelopment of the FS in nonsyndromic adults could be an expression of an elevated intracranial pressure during early development as an after-effect of certain condition.

Incidence of a Bifid Mandibular Condyle in Dry Mandibles.

BACKGROUND: A bifid mandibular condyle (BMC) is a rare anatomical variation with an etiology not fully understood. Although there are numerous case reports regarding it, purposeful epidemiological investigations on the BMC frequency among different groups are scarce. This study aims to investigate the incidence and laterality of BMC among series of adult males from Bulgaria and perform a morphometric analysis of it. MATERIALS AND METHODS: A series of 500 dry intact mandibles from adult males was investigated. The condyles were macroscopically observed and when skulls were available, the corresponding mandibular fossae were also inspected. In the cases when bifid condyles were found, 27 measurements were taken. RESULTS: Bifid mandibular condyle was observed in 4 (0.8%) mandibles. All of the cases were unilateral, 2 on the right side (0.4%) and 2 on the left (0.4%). The condyles were divided into medial and lateral heads by a sagittal fissure or a notch. CONCLUSION: The established frequency of BMC was comparable with those reported in Turkish and Korean populations. The lack of injury marks and traces implies a developmental etiology of this condition.

Sex estimation based on mandibular measurements.

Medical imaging and machine learning are beneficial approaches in physical and forensic anthropology. They are particularly useful for the development of models for sex identification based on bone remains. The present study uses machine learning algorithms to create models for sex estimation based on mandibular measurements. The sample included head CT scans of 239 adult Bulgarians (116 males and 123 females). Three-dimensional coordinates of 45 landmarks of the mandible were acquired from segmented polygonal models of the skulls of these individuals. Two datasets of mandibular measurements were assembled. The first dataset included 51 measurements: linear, projective, and angular measurements. The second dataset included 990 interlandmark distances. Seven machine learning algorithms (Support Vector Machines, Neural Network, Naïve Bayes, Random Forest, J48, JRip, and Logistic Regression) were applied to the two datasets, and the classification accuracy was evaluated by 10x5-cross-validation. The selection of the best subsets of attributes specific to each of the abovementioned algorithms was done based on the attribute importance evaluated by an attribute selection scheme. In general, the sub-symbolic algorithms achieved higher results than the symbolic ones, except for the logistic regression. The best classification model was learnt by the Support Vector Machines algorithm, which achieved an accuracy of 95.3% on a dataset described by 19 interlandmark distances. In both datasets, the application of advanced attribute selection has led to an increase in the classification accuracy of all algorithms used in the experiments.

Osseous Bridges of the Sphenoid Bone: Frequency, Bilateral and Sex Distribution.

Sellar (caroticoclinoid and interclinoid), pterygospinous and pterygoalar bridges are osseous bars of the sphenoid bone, which enclose additional foramina in the skull base and could cause entrapment of nerves, occlusion of vessels and obstruction of surgical corridors. This study aimed to investigate the frequency of sphenoid bone bridges in Bulgarians and to assess the bilateral and sex differences in their distribution. This study was performed on head CT scans of 315 Bulgarians, 148 males and 167 females. The sellar bridges were the most common type of sphenoid bridging; particularly the caroticoclinoid bridge. The pterygospinous bridge was a relatively common finding and the pterygoalar bridge was the most infrequent type of bridging. The total frequency of sellar bridges did not differ significantly between both sides and sexes. The pterygospinous bridge did not indicate significant bilateral differences but showed considerable sex differences concerning the left-side occurrence, which was significantly higher in the male series. There were no considerable bilateral and sex differences in the distribution of the pterygoalar bridging. There were no significant correlations between the different types of sphenoid bone bridges, but each type of bridging showed significant positive correlations between the right and left side co-occurrence in males and females.

Size and shape of human mandible: Sex differences and influence of age on sex estimation accuracy.

The degree of sexual dimorphism expressed by human bones is of primary importance for the development of accurate methods for sex estimation. The objective of the present study was to investigate sex differences in shape and size of the mandible using geometric morphometric methods. The study also aimed to examine the impact of age on the sex classification ability of the size and shape of the mandible. Computed tomography images of 190 Bulgarians (98 males and 92 females) were used in the study. Polygonal surface models of the skulls were generated and used for digitizing 45 landmarks located on the mandible. The raw three-dimensional coordinates of the landmarks were processed via generalized Procrustes superimposition. The sex differences in mandibular size and shape were evaluated for statistical significance. Multivariate regression was applied for correction of the allometric effect. Principal component analysis, discriminant analysis, and canonical variate analysis were also used in the study. Mandibular size differed significantly between males and females and achieved a sex classification accuracy of 87%. The significance of the sex differences in mandibular shape depended on the type of shape variables used in the analysis. The shape variables provided different classification accuracy: 78% using the Procrustes coordinates and 53% using the regression residuals. The male and female mandibles differed significantly in size and shape, including the allometric component. Mandibular size is a more effective sex indicator than shape. Age has an ambiguous effect on the classification accuracy of the size and shape variables of the mandible.

Cranial morphology in metopism: A comparative geometric morphometric study.

BACKGROUND: Cranial sutures are active bone growth sites and any alteration in their normal formation, patency and closure influences the overall cranial morphology. This comparative study aims to establish whether the cranial shape and size are significantly modified when metopic suture persists into adulthood using geometric morphometric analyses. METHODS: The sample consisted of 63 metopic and 184 non-metopic dry adult male crania. Three-dimensional polygonal models of the crania were generated using a hand-held laser scanner Creaform VIUscan. A total of 50 landmarks were digitized on the three-dimensional models and eight landmark configurations delineating the cranium and its compartments were constructed and analyzed. Geometric morphometric analyses were applied to investigate separately the size and shape differences between the metopic and non-metopic series in each of the landmark configurations. RESULTS: Significant size differences were established solely in the neurocranium, but not in its total size, rather in its parts. The size modification was expressed by an enlargement of the anterior part of the neurocranium at the expense of the middle and posterior ones. All investigated landmark sets differed significantly between the series regarding the shape. In metopic series, the shape alteration was mainly in a mediolateral widening and an anteroposterior shortening contributing to a more rounded overall shape of the cranium. CONCLUSIONS: The slight modification of the cranial morphology in metopism suggests that the metopic suture persistence is not an isolated variation limited to the frontal bone. It is rather a complex condition associated with a combination of specific phenotypic characteristics.

Influence of persistent metopic suture on sagittal suture closure.

BACKGROUND: Metopic suture lies between the halves of the growing frontal bone and usually closes in early infancy. If the metopic suture fails to close it persists in adulthood and could be considered an anterior continuation of the sagittal suture (SS). This study aimed to investigate if the metopic suture persistence is related to any significant deviations from the normal SS maturation. We also aimed to elaborate linear regression models for age-at-death prediction of the metopic crania and to compare their accuracy with the models developed on the control ones. METHODS: The SS was investigated in a total of 122 dry adult contemporary male crania of known age-at-death divided in a metopic series (n = 34) and a control one (n = 88). The crania were scanned and high-resolution volumetric images were generated using an industrial µCT system. The SS closure degree was assessed on cross-sectional tomograms using a scale of grades. Both series were compared and linear regression models for age-at-death prediction were elaborated. RESULTS: The comparison between both series showed that the degree of SS closure differs significantly in all SS sections and bone layers and it is considerably lower in the metopic series. The elaborated linear regression models showed that the error in the age-at-death prediction of the metopic crania is almost two times bigger than that in the control. CONCLUSIONS: The SS closure in metopic crania is significantly delayed compared to the control, which means that it is entirely unreliable and misleading as an indicator for age-at-death prediction.

A Geometric Morphometric Study on Sexual Dimorphism in Viscerocranium.

The level of sexual dimorphism manifested by human bones is an important factor for development of effective sex estimation methods. The aim of the study was to investigate the sexual dimorphism in the size and shape of the viscerocranium using geometric morphometric techniques. It also aimed to explore the sex differences in distinct viscerocranial regions and to establish the most dimorphic region with regard to size and shape. Computed tomography images of 156 males and 184 females were used in the study. Three-dimensional coordinates of 31 landmarks were acquired. Five landmark configurations were constructed from the viscerocranium and its orbital, nasal, maxillary, and zygomatic region. Generalized Procrustes superimposition, principal component analysis, and discriminant analysis were applied to each configuration. The significance of the sex differences in size and shape was assessed and significant differences were found in all configurations. The highest accuracy was obtained from both shape and size of the whole viscerocranium. Based on size only, the highest accuracy was achieved by the nasal region. The accuracy based on shape was generally low for all configurations, but the highest result was attained by the orbital region. Hence, size is a better sex discriminator than shape.

Squamous suture obliteration: frequency and investigation of the associated skull morphology.

This study aimed to investigate the frequency of squamous suture (SqS) obliteration, to estimate the involvement of the major calvarial sutures and those surrounding the temporal squama, and to inspect the neuro- and basicranium for deformities. A series of 211 dry skulls of contemporary adult males were macroscopically observed. The skulls with closed SqS were scanned using an industrial µCT system. Digital morphometry of the skulls with obliterated SqS was performed by recording the 3D coordinates of anatomic landmarks and calculation of linear distances, angles and indices. Obliteration of SqS was observed in 3 (1.42%) skulls. One skull showed bilateral SqS obliteration. The other two cases were unilateral, one right-sided and one left-sided. SqS obliteration seems to be co-ordinated with the closure of the parietomastoid suture, partially related to the closure of the occipitomastoid, sphenoparietal and sphenofrontal sutures, and independent from the closure of the sphenosquamosal suture and the major calvarial sutures. No severe disproportions in the skull configuration were observed in the three investigated cases. The major differences in the complimentary hemicrania concern the parietal and occipital parts of the skull vault. Dorsum sellae erosion, an indicator for raised intracranial pressure, was observed in all three cases.

A comparative digital morphometric study of nasofrontal region in metopic and non-metopic cranial series.

This study aimed to compare the nasofrontal region in metopic and non-metopic cranial series and to assess whether the persistent metopic suture is related to a specific morphology of this part of the cranium. For the purpose of the study, a total of 159 dry crania (control series n = 90 and metopic one n = 69) of contemporary adult males were scanned with a laser scanner. Digital morphometry was accomplished by recording the three-dimensional coordinates of eleven landmarks, 3 bilateral and 5 in the mid-sagittal plane, characterizing the nasofrontal region. Between these landmarks, 43 linear measurements were calculated as Euclidian distances and 25 triangles were constructed. The angles, areas and heights of these triangles were also computed. The results show that the metopic crania have a distinctive nasofrontal morphology as the significant differences are not in the forehead height, but mainly in its configuration and in the nasal bones dimensions. The metopic crania have significantly flattened glabella, broad interorbital distance and wider, shorter and less prominent nasal bones compared to the non-metopic ones.

Data mining for peculiarities in the configuration of neurocranium when the metopic suture persists.

The persistent metopic suture is an anatomic variation related to a specific skull configuration. Data on the proportionality of the neurocranium and the occurrence of additional variations when the metopic suture persists are still insufficient. This study presents a comparison between a metopic and a non-metopic homogenous cranial series. The most distinctive quantitative and qualitative characteristics of the skull configuration when the metopic suture persists were identified using data mining techniques. A total of 175 contemporary adult male skulls were investigated. The skulls were divided in two groups: a control series (n = 100) and a metopic series (n = 75). All skulls were scanned with a hand-held laser scanner CreaformVIUscan and polygonal models were created. For 150 of the skulls, industrial µCT scanning was performed using Nikon XT H 225 and volumetric images were generated. A total of 92 attributes, both quantitative (dimensions) and qualitative (anatomical variations of the skull), were recorded from the 3D models. The major distinctive peculiarities observed in the neurocranial configuration when the metopic suture persists concerned the dimensions of the frontal bone which was considerably shorter, wider and more convex compared to the control. The metopic skulls manifested wormian bones in the sphenoidal fontanelle, around the temporal squama and along the lambdoid suture. These supernumerary bones were considerably more common in the metopic series in comparison with the control. The most reliable model resulting from the data mining summarizes a total of five classification rules entirely based on quantitative characteristics of the frontal bone.

Impact of Resolution and Texture of Laser Scanning Generated Three-Dimensional Models on Landmark Identification.

The aim of the study was to determine the impact of the resolution and texture of three-dimensional (3D) models created through laser scanning on the measurement error (ME) of craniometric landmarks. Ten skulls were scanned at five different resolutions, and the generated 3D models were exported with and without texture. The 3D coordinates of 28 landmarks were derived. Each landmark was picked five times by one observer. The ME of a definite landmark was calculated as an average of distances between the repeated placements of the landmark by the observer and the landmark centroid. One-way analysis of variance was applied for detection of significant differences in the MEs between and within landmark types recorded at different resolutions. The MEs of landmark types in textured and nontextured models were compared by a paired test. Twelve linear measurements were calculated as interlandmark distances, and their values obtained on the models of different resolution were compared. The Frankfurt horizontal plane was constructed for each model and its deviation was calculated at different resolutions. Scan resolution impacted MEs of Type 1 and Type 2 landmarks but not the precision level of Type 3 landmarks. Texture most influenced the precise identification of Type 1 landmarks. The interlandmark distances between Type 2 landmarks were most consistent in their values, those between Type 1 landmarks showed deviations in low-resolution models, and distances between Type 3 landmarks demonstrated various patterns of transition of the values throughout the resolutions. Altogether, the use of textured high-resolution models would be preferable in morphometric studies. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1950-1965, 2020. © 2019 American Association for Anatomy.

Data mining for sex estimation based on cranial measurements.

The aim of the present study is to develop effective and understandable classification models for sex estimation and to identify the most dimorphic linear measurements in adult crania by means of data mining techniques. Furthermore, machine learning models and models developed through logistic regression analysis are compared in terms of performance. Computed tomography scans of 393 adult individuals were used in the study. A landmark-based approach was applied to collect the metric data. The three-dimensional coordinates of 47 landmarks were acquired and used for calculation of linear measurements. Two datasets of cranial measurements were assembled, including 37standard measurements and 1081 interlandmark distances, respectively. Three data mining algorithms were applied: the rule induction algorithms JRIP and Ridor, and the decision tree algorithm J48. Two advanced attribute selection methods (Weka BestFirst and Weka GeneticSearch) were also used. The best accuracy result (91.9 %) was achieved by a set of rules learnt by the JRIP algorithm from the dataset constructed by application of the GeneticSearch selection algorithm to the dataset of standard cranial measurements. The set consisted of five rules including seven cranial measurements. Its accuracy was even better than the classification rates achieved by the logistic regression models. Concerning the second dataset of nonstandard measurements, the best accuracy (88.3 %) was obtained by using classification models learnt by two algorithms - JRIP with a dataset preprocessed by the BestFirst selection algorithm and Ridor with preprocessing by the GeneticSearch selection algorithm. Our experiments show that for the two datasets mentioned above the rule-based models contain smaller sets of rules with shorter lists of measurements and achieve better classification accuracy results in comparison with decision tree-based models.

Sex estimation by Mastoid Triangle using 3D models.

Mastoid Triangle (MT) is a triangle constructed between the landmarks porion, mastoidale and asterion. The aim of the study is to evaluate the sex differences in the MT size in Bulgarian adults and to develop discriminant functions for sex estimation based on the MT sides and area. The study was carried out on 148 head CT scans. A sample of 53 males and 53 females was used for development of discriminant functions, and a test sample of 21 males and 21 females was applied for their validation. Using the software InVesalius©, 3D models of the skulls were segmented and exported in STL format. The 3D coordinates of the landmarks porion, asterion and mastoidale were collected using the software MeshLab©. The MT sides, area and angles were calculated. The sex differences were assessed by the independent t-test. Bilateral differences were evaluated using the paired t-test. Univariate and multivariate discriminant function analyses were applied. The results showed that the MT sides and area differed significantly between both sexes. Sex differences were also established for the angle at mastoidale. Bilateral differences were found in males for the distance porion-mastoidale, which was significantly greater on the right side. The MT dimensions showed sufficient discriminating power for sex estimation among Bulgarians (up to 89%), and the total MT area proved to be the best single sex discriminating trait. The test sample corroborated the usefulness of the MT in sex estimation demonstrating similar or higher overall accuracy rates.

Sex estimation by size and shape of foramen magnum based on CT imaging.

Foramen magnum (FM) has a well-protected position, which makes it of particular interest in forensic research. The aim of the study is to assess the sex differences in size and shape of FM, develop discriminant functions and logistic regression models based on the FM measurements, compare the accuracy results of the measurements obtained through different measuring approaches, and establish the most reliable variables for sex estimation in Bulgarian adults. Head CT scans of 140 Bulgarian adults were used in the study. The segmentation of the skulls was performed in the software InVesalius. The length, breadth, circumference, and area were measured based on the 3D coordinates of definite landmarks and semi-landmarks. The circumference and area were calculated regarding the foramen as a 2D and 3D structure. Two additional variables (λ2 and λ3) corresponding to the least square errors along the length and breadth directions at the fitting of the 3D coordinates to a plane were examined for their sex discriminating ability. The FM shape was classified based on the values of the FM index. The significance of the sex differences was assessed. Discriminate function analysis and binary logistic regression were conducted. Significant sex differences were established in the FM size and shape. The eigenvalue λ3 is the best discriminating parameter applying discriminant function analysis. The acceptance of FM as a 2D or 3D structure does not provide substantial information for its sex discrimination. The measurements of FM do not offer sufficiently high predicting rates for sex estimation in the Bulgarian population.

Morphometric study of the mylohyoid bridging in dry mandibles.

ABSTRACT: The mylohyoid bridging is a hyperostotic variation representing formation of bony bridges over the mylohyoid groove. The goals of this study were to establish the frequency of mylohyoid bridging in contemporary and medieval series from Bulgaria and to examine the changes in the prevalence through time, to assess and compare the different types of mylohyoid bridging, to establish the patterns of distribution with respect to laterality, sex and age and to accomplish a morphometric analysis. Materials and methods: The study was performed on a total of 448 intact dry mandibles of adult individuals from both sexes, grouped into contemporary male, medieval male and medieval female series from Bulgaria. The individuals in the series were distributed into two age cohorts: between 20-40 years old and above 40 years. Мacroscopic, metric and statistical analyses were performed. Results and Conclusions: The frequency of the mylohyoid bridging was 10.99% (21 out of 191 mandibles) for the contemporary male series, 9.45% (12 out of 127) for the male series and 7.69% (10 out of 130) for the medieval female series. The comparison between both male series indicated slightly increasing of the mylohyoid bridging with time. No significant bilateral and sex differences in the frequency and pattern of distribution of the mylohyoid bridging were established. The most common type of bridging was the distal one. The dependence of the mylohyoid bridging on the aging is controversial since in the female series its frequency was significantly higher in the individuals over 40 years, while in both male series it did not differ considerably between the age groups. The metric analysis did not show significant differences between the male series. However, the sexual differences were noteworthy with respect to the whole length of the mylohyoid groove and the distance between the bridge and the distal point of the mylohyoid groove. Furthermore, the considerable differences between the metric characteristics of lingular and distal type showed that this approach is useful and could be applied for precise differentiation of the mylohyoid bridging types. During the investigation, we also observed several cases of an accessory groove in the region of the mylohyoid groove. This additional groove most probably reflects variations in the branching patterns of the inferior alveolar nerve and/or mylohyoid nerve and could be of importance in oral surgery and dental practice.