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.

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 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.

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.

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.

Facial soft tissue thicknesses in Bulgarian adults: relation to sex, body mass index and bilateral asymmetry

BACKGROUND

The aim of the study is to measure the facial soft tissue thicknesses (STTs) in Bulgarians, to evaluate the relation of the STTs to the nutritional status, sex and bilateral asymmetry, and to examine the correlations between the separate STTs as well as between the STTs and body weight, height, and body mass index (BMI). In the present study, the facial STTs were measured on computed tomography scans of the head of Bulgarian adults.

MATERIALS AND METHODS

The STTs were measured at 7 midline and 9 bilateral landmarks. The measurements were performed in the free software InVesalius in the axial and sagittal planes. The mean, standard deviation, minimum and maximum values, median and coefficient of variation were reported for the STT at each landmark according to the sex and BMI category. The BMI, sex and bilateral differences were assessed for statistical significance. Pearson correlation analysis was applied to assess the strength and direction of the relationships between the STTs and body height, weight and BMI, as well as between separate STTs.

RESULTS AND CONCLUSIONS

The facial soft tissues in Bulgarian adults changed in accordance with the nutritional status of the individual and in both sexes all STTs augmented with the increasing BMI. For both normal and overweight BMI categories, males had more soft tissue at the majority of facial points than females, as the only exceptions were observed in the cheek zone, where STTs were thicker in females. Significant bilateral differences were observed in either sex and BMI category. Stronger correlations were established for the STTs in the jaw region and between the cheek and jaw soft tissues. Besides, the correlations between the homologous bilateral landmarks were among the strongest ones.

Variations in the squamous part of the occipital bone in medieval and contemporary cranial series from Bulgaria

The squamous part of the occipital bone is a place of many different variations. They are a result of faulty ossification in the occipital squama or due to the presence of sutural bones in the lambda region. As their differentiation is intricate because of the various criteria used, the issue of their recognition in the adult skull still remains difficult even though they can be clearly distinguished at a younger age. The aim of the present study was to compare the frequency of interparietal, preinterparietal and sutural bones in the lambda region in medieval male and female cranial series as well as between medieval and contemporary male series from Bulgaria. We also discuss the development of the occipital squama in order to set clearer criteria for further differentiation of such variations in the adult skull. In the reviewed 3 cranial series, the variations in the squamous portion of the occipital bone were observed with a low frequency. The incidence of preinterparietal bones was more common than the interparietal ones. The sutural bones in the lambda region were numerous in the series. No statistically significant sex or intergroup differences were established. So even if these anatomical variations are relatively rare, the understanding of them is of significance for many disciplines like anthropology, comparative and developmental anatomy, clinical and forensic medicine.

Morphology of suprascapular notch in medieval skeletons from Bulgaria

The suprascapular notch is situated in the lateral part of the superior border of the scapula, just medial to the base of the coracoid process, giving passage for the suprascapular nerve. The aim of this study is to determine the frequency of different types of suprascapular notch in male and female medieval skeletal series and to assess the sexual differences. The shape of the notch was classified into 5 types, based on the scheme given by Alekseev. A total of 102 scapulae and scapular fragments were investigated. The results show that the deep notch was the most common. In the left female scapulae the shallow notch was frequently observed as well. Three cases of suprascapular foramen, which is considered as a risk factor for suprascapular nerve neuropathy, were observed and there was a double foramen in one of them, which is a very rare case. According to the results of c2 test, there were no significant sexual differences in the distribution of notch types. Our results illustrate that there were some individuals among the investigated medieval population potentially affected by suprascapular nerve entrapment syndrome and their way of livingmay have been impacted by the symptoms accompanying this condition.