Sexual features of facial skull asymmetry according to spiral computed tomography

Introduction

The fact of facial asymmetry in people is generally acknowledged. One of the reasons for this asymmetry is an uneven assembly of skull bones elements [1]. For many years, traditionally, the main method of analysis of the morphology of the facial skull and diagnostics of facial bones deformation was X-ray imaging. However, it is difficult to evaluate the asymmetry of the facial skull because of numerous overlapping anatomic structures [2]. Computer-assisted craniometry is a vast field of study because tomographic studies of high resolution have become acknowledged standards of diagnostic [3]. The results of craniometry of macerated skulls, X-ray images, and spiral computed tomography show that spiral computed tomography (SCT) can be useful and alternative to a regular X-ray [4]. The results of the measurements obtained from SCT are precise and comparable with the results of anthropometric analysis of a macerated skull [5][6][7], which expands the clinical application of SCT [8][9].

It is known that the individual shape of the face determines the physiological asymmetry of the facial skull [10]. Along with this, such asymmetry of bone structures of the skull in modern people is understudied, in particular, in a sex-related aspect [4][11]. Thus, a comparative analysis of craniometric parameters in persons of both sexes residing in the Rostov Region is acute and relevant.

The study aimed to evaluate the degree of expression of asymmetry of linear sizes of the facial skull that are the most significant in determining asymmetry in persons of both sexes by the results of SCT.

Materials and Methods

SCT scans of 104 people of both sexes (52% of women (n = 54) and 48% of men (n = 50)) were studied. SCT was performed at the facilities of the department of magnetic resonance imaging and computed tomography at the Rostov State Medical University in patients with suspected vascular pathology of the brain.

Criteria of inclusion:

• suspected vascular pathology of the brain;
• lack of skull bone pathology;
• lack of anomalies in the development of skull bone;
• lack of anomalies in the development of the skull in general.

Criteria of exclusion:

• children and adolescents (before the end of the facial skull formation);
• macroscopic signs of pathological changes in the facial skull;
• anomalies in the skull development.

For the analysis of the obtained results, the authors used axial, MPR (multiplanar reconstruction), and SSD (surface shadow density) reconstructions of the skull in different projections. The measurements were made using a standard digital scale of the operating station of a computed tomograph.

The shapes of the brain and facial skull were determined by the dimensions of a cephalic index [12]. A “fan” method was used in SCT scanning [13][14] in the upper, lower, and lateral fans for the measurement of the distance from standard points nasion, supraspinal, and zygomaxilar to non-standard points from each side. This method included the study of 27 linear dimensions of the facial skull from each side.

Processing of the statistical data was performed using the Excel software package recommended for the statistical analysis of medical-biological data. For each studied parameter, the authors calculated the sample mean value (M) and the standard error of the mean (m). The significance of the differences in the mean values was evaluated using Student’s parametric criterion for normal distribution of the initial data. The differences between the groups of parameters were considered significant at p < 0.05.

According to the recommendations of Efimova et al. [15], during the calculation of the coefficient of variation (kv=δ/M – the ratio of the standard deviation of linear dimensions to the arithmetic mean of these dimensions), kv < 10 % was considered to be a weak expression, 10% < kv < 25% was considered to be a moderate expression, and kv > 25% – a high degree of expression. The method of Gaivoronskiy et al. [10] was used to evaluate mean linear dimensions of the facial skull on the right and left, to calculate the differences between them in the sigmas, and the degree of expression of asymmetry of the facial skull within the sigmas 1, 2, and 3.

Results

During the distribution of material depending on the sex, SCT in men and women revealed significant differences in 27 linear dimensions of the facial skull in the upper, lower, and lateral “fans” on both sides (Table 1).

SCT revealed right-sided asymmetry of linear dimensions of the facial skull in all “fans” in men. In women, SCT revealed right-sided asymmetry in the upper and lateral “fans” and left-sided asymmetry in the lower “fan”.

In the majority of cases, the coefficient of variation of the studied linear dimensions of the facial skull did not exceed 10–20%, which indicated the weak and moderate variation of the parameters of each dimension and their consistency.

In the groups of males and females, SCT images were used to determine the occurrence rate of asymmetries by the intervals of sigmas of these dimensions. In the series of SCT of men (Fig. 1), in the upper, lower, and lateral “fans”, the differences in the parameters on both sides did not exceed 1 ϭ in 67.6%, 74.9%, and 64.3% of cases, respectively; they were within 2 ϭ (in 25.7%, 15.6%, and 30.3% of cases, respectively); and they were within 3 ϭ (in 6.8%, in 8.6%, and 5.4% of cases, respectively). In the series of SCT of women (Fig. 2), in the upper, lower, and lateral “fans”, the differences on both sides did not exceed 1 ϭ in 68.8%, 63.8%, and 65.0% of cases; the differences were within 2 ϭ (in 26.3%, 32.5%, and 32.8% of cases, respectively); and they were within 3 ϭ (in 4.9%, 3.7%, and 2.2% of cases, respectively).

The authors revealed statistically significant differences in the degree of asymmetry in the facial skull linear dimensions in both sexes. In the upper “fan”, the distances from nasion to zygomaxilar (N-Zm) and from nasion to frontonazale (N-Fn) prevailed in both sexes on the right. In the lower “fan”, the distances from the supraspinal to zygomaxial (Ss-Zm) prevailed in women and men on the left side. In the lateral “fan”, the distance from the zygomaxial to frontonazale (Zm – Fn) prevailed on the right side in both sexes.

Discussion

The revealed differences in the linear dimensions of the facial skull prevailed in men in comparison with women. These data corresponded to the data published by Alieva et al. [11].

SCT showed a prevalence of various asymmetries of the facial skull right-sided linear dimensions in men in all the “fans”. In women, right-sided asymmetry prevailed in the upper and lateral “fans” and left-sided asymmetry prevailed in the lower “fan”. These data do not agree with the respective data published by Alieva et al. [11] but confirm the data obtained by Gaivoronskiy et al. [13].

In the male and female groups, the sigma intervals of facial skull linear dimensions were used to evaluate the occurrence rate of asymmetry of varying severity. In the male and female groups, in the upper, lower, and lateral “fans”, there were differences revealed in parameters from both sides. Primarily, they did not exceed 1 or 2 ϭ. According to some authors [10][13], if the differences in the parameters from the left and right sides of the facial skull were within 1 ϭ, the revealed asymmetry was insignificant and physiological. If they were within 2 ϭ, the asymmetry was moderate, which did not require correction.

Conclusion

The analysis of SCT scans revealed sex-related differences in the linear dimensions of the facial skull. The majority of differences significantly prevailed in men.

SCT craniotomy in the upper, lower, and lateral “fans” revealed asymmetry of facial skull linear dimensions in men and women in the upper, lower, and lateral parts of the skull.

Right-sided asymmetry in the facial skull linear dimensions prevailed in all “fans” in men. In women, right-sided asymmetry prevailed in the upper and lateral “fans”, and left-sided asymmetry – in the lower “fan”.

The most expressed asymmetry in the facial skull linear dimensions was revealed in both sexes. In the upper “fan”, these dimensions were nasion-zygomaxial (N-Zm) and nasion-frontanazale (N-Fn) that prevailed in both sexes. In the lower “fan”, the asymmetry prevailed in the distance from supraspinal to zygomaxial (Ss-Zm) and from zygomaxial to frontanazale (Zm-Fn) in both sexes.

The revealed asymmetry in the facial skull linear dimensions of mild and moderate degree determines the individual shape of the face in both sexes. The obtained data on craniometry parameters can be used in clinical practice by radiologists, plastic surgeons, maxilla-facial surgeons, as well as anthropologists and forensic specialists.