|Year : 2021 | Volume
| Issue : 1 | Page : 9-13
Morphometric analysis of foramen magnum in the determination of sex using computed tomography
Bashir Ahmad Wani, Nusrat Nazir, Rayees Ahmad Sheikh, Altaf Hussain Chalkoo, Tauseefa Jan
Department of Oral Medicine and Radiology, Government Dental College, Srinagar, Jammu and Kashmir, India
|Date of Submission||09-Sep-2020|
|Date of Decision||23-Nov-2020|
|Date of Acceptance||03-Mar-2021|
|Date of Web Publication||24-Mar-2021|
Bashir Ahmad Wani
Department of Oral Medicine and Radiology, Government Dental College, Shreenbagh, Karan Nagar, Srinagar, Jammu and Kashmir
Source of Support: None, Conflict of Interest: None
Background: sex identification by morphological assessment of various bones of the skeleton had been one of the oldest approaches in forensic anthropology and medico-legal cases. Aim and Objective: The aim of this study was to make the morphometric measurements of the foramen magnum in determining the feasibility of sex determination using computed tomography (CT). Materials and Methods: The data for our study was obtained from 100 patients having CT scan of the head and neck region (Siemens Somatom 256 slice CT scanner) with 1mm contiguous axial scans using bone window settings (2000 HU with 400 HU in centre), scan time of one second and exposure parameters 140 kVp and 70mA. The different measurements taken include the antero-posterior (AP) diameter, transverse diameter and area of the foramen magnum. Results: There were 50 males and 50 females with the age range of 18 to 75 years. Males have a higher average value than females in all of the parameters measured on foramen magnum. By using Student's T-test, all the measured parameters showed significant difference between the sexes (p < 0.01). Conclusion: The expression of sexual dimorphism in the foramen magnum region shows significant difference between the sexes, therefore this area of the skull should be considered a useful area in the identification of sex.
Keywords: Computed tomography, foramen magnum, sex determination, sexual dimorphism
|How to cite this article:|
Wani BA, Nazir N, Sheikh RA, Chalkoo AH, Jan T. Morphometric analysis of foramen magnum in the determination of sex using computed tomography. J Forensic Sci Med 2021;7:9-13
|How to cite this URL:|
Wani BA, Nazir N, Sheikh RA, Chalkoo AH, Jan T. Morphometric analysis of foramen magnum in the determination of sex using computed tomography. J Forensic Sci Med [serial online] 2021 [cited 2022 Oct 2];7:9-13. Available from: https://www.jfsmonline.com/text.asp?2021/7/1/9/311859
| Introduction|| |
Sex identification by morphological assessment of various bones of the skeleton had been one of the oldest approaches in forensic anthropology and medico-legal cases. Determination of sex in unidentified skeletons is not always an easy and correctly performed procedure particularly in explosions, wars and other mass disasters-where identification of sex may be extremely complicated because of skeletal fragmentation. Therefore, sex determination of an individual is one of the principal biological indicators of identity, in cases of mass disasters like wars, plane crashes, terrorist attacks, bomb explosions, and natural calamities like fire, earthquakes, etc. The skull, pelvis, and femora are the most useful bones for the determination of sex of an individual. It is relatively easy to achieve accuracy in the identification of sex when the remnants of an individual are complete. However, fragmented or dispersed remains of an individual results in an incomplete assessment base with some aspects of identity being inconclusive. Sex is one of the important biological properties of an individual and has been accurately determined from skeletal remains of the human pelvis and cranium of full skeleton. The bones of the craniofacial skeleton are usually the best preserved in human beings and has paved a way for recognition of human corpses when badly damaged.
Studies have revealed that skull is the most easily accessible portion of the skeleton after the pelvis that has provided an accuracy of up to 92%. The more resistant small skeleton remnants of the skull can be used in the determination of sex in these cases. There are various bones of the craniofacial skeleton that play an important role for the purpose of sex determination which are mandible, maxillary sinus, cranial base, and mastoid triangle.,,, The cranial base is relatively thick, protected due to its anatomical position and its resistance to physical damage. As such it has offered better results than any other parts of the skull to determine sex of an individual. Therefore, this region has played important role in the process of sex determination in cases of mass disasters and natural calamities such as plane crash, fire, earth quakes, and building collapses. The foramen magnum is present in the occipital bone which is one of the most resistant skeleton parts of the cranial base. It is a transition zone between the spine and cranium that can act as an important landmark with its adjacent vital structures such as the cerebellum, medulla oblongata, and spinal cord. Various important structures pass through it including lower part of medulla oblongata, nerves, and vessels. Hence, this region plays a very important role in the determination of sex particularly in mass disasters.
Catalina-Herrera in his study on the Spanish population indicated that both the sagittal as well as transverse dimensions of the FM were significantly higher in male than in female skulls. Zaidi and Dayal had classified a sample of Indian skulls according to the shape and dimensions of the FM, reporting sex differences which were similar to those reported among Brazilian skulls. Yusal et al. reported sexual dimorphism by analyzing the dimensions of FM using three-dimensional (3D) computed tomography (CT) with an accuracy of 81%.
Therefore, this study was conducted with the aim, to make the morphometric measurements of the foramen magnum in determining the feasibility of sex determination using CT and describe the variables of the foramen magnum of the Kashmiri population in comparison with other populations.
| Materials and Methods|| |
This observational study included 100 adult patients having CT scan of the head-and-neck regions done for some other reasons such as sinusitis, headaches, nonspecific temporomandibular joint pain, and trauma. Inclusion criteria include patients with nonspecific symptoms such as headache, dizziness, and sinusitis. Patients with fractures of the head and neck, diseases involving bones of the head and neck and advanced degeneration in the head-and-neck region were excluded from the study. After taking approval from the Head of the Department and ethical committee of the institution, standardized CT protocol for the head and neck region was used with Siemens Somatom 256 slice CT scanner with 1 mm contiguous axial scans using bone window settings (2000 HU with 400 HU in centre), scan time of 1 s and exposure parameters 140 kVp and 70 mA. After the examination, the volumetric data were reoriented and transferred to a workstation to perform multi-planar reconstructions to obtain transverse, sagittal, and coronal images. Dicom viewer “Onis 2.6 Professional” was used for the measurements of the foramen magnum. The slice with the widest diameter of the foramen magnum was obtained and the transverse diameter (TD) was measured, followed by measuring the area of the foramen magnum by manually drawing automatic area calculator program [Figure 1]. Antero-posterior (AP) diameter was measured using widest diameter slice on sagittal section [Figure 2]. All the measurements were re-obtained after 2 weeks by the same observer and the average of these two measurements were noted.
|Figure 1: Image showing the transverse diameter measured and the area of the foramen magnum by manually drawing automatic area calculator program|
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|Figure 2: Image showing antero-posterior diameter measured by using widest diameter slice on sagittal section|
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IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp. and Microsoft Excel (version 5.00) were used to carry out the statistical analysis of data. Compliance of the normal distribution of data was analyzed by Kolmogorov–Smirnov test. Data were analyzed using means of descriptive statistics, namely mean and standard deviations. Student's independent t-test was employed for comparison of groups. Fisher's coefficients were used to compare the relative importance of the nonuniform data. A P < 0.01 was considered statistically significant. Using discriminant analysis, the rate at which gender could be correctly identified was calculated as a percentage. ROC analysis was performed to select the discriminant point (cutoff) for checking univariate predictive accuracy. To see the overall predictive accuracy of the combined parameters, multivariate discriminant function analysis was performed.
| Results|| |
There were 50 male and 50 female patients with age range of 18–75 years. After examining all CT scans of these patients, mean AP diameter was 35.90 ± 2.75 mm, mean TD was 31.79 ± 2.97 mm, and mean area was 9.06 ± 1.58 cm2 [Table 1].
The results of the descriptive statistics showed that the differences between all male and female variables investigated display statistically significant differences (P < 0.01). In males mean AP diameter was 36.89 ± 3.15 mm, TD was 32.47 ± 2.87 mm, and the area was 9.15 ± 1.28 cm2. In females, mean AP diameter was 34.91 ± 1.82 mm, TD was 31.11 ± 2.94 mm, and the area was 8.97 ± 1.84 cm2 [Table 2]. According to Student's t-test results, there was statistically significant difference between the sexes in all of the parameters measured (P < 0.01).
Each measured variable from the foramen magnum was considered as univariate for sex differentiation and the most reliable variable was AP diameter with 72% sex differentiation value for all groups. The most reliable discriminant variable was area (88%) in males and AP diameter in females (68%) as shown in [Table 3].
The results of the descriptive statistics for the 100 crania [Table 4] show that the differences between all male and female variables investigated display statistically significant differences (P < 0.01).
When multivariate discriminant function test was performed for all the variables, the discrimination rate was 72% for all males, 88% for all females and 80% for both sexes as shown in [Table 5].
The prediction percentages for a combination of foramen magnum variables from our study show similar levels of prediction when compared to studies of other populations. [Table 6] shows comparison in the predicted accuracy among various studies.
|Table 6: Predicted accuracy in different studies among various populations|
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| Discussion|| |
The methods of sex determination may vary and depend on the condition of the available skeletal remains. Therefore, more resistant small skeleton remnants of the body play an important role in the determination of sex in cases of partial skeletal remains. Various bones of the skeleton like pelvis, cranial base, mandible, and lots of other bones have been used for the purpose of sex determination. The cranial base as a part of the cranium is most likely to remain intact after the action of time and the environment. The measurements of the foramen magnum to aid in the diagnosis of sex has been studied around the world, and the results have been controversial.
In a study conducted by Kamath et al., on Indian population, the mean AP diameters were 33.21 mm and 30.99 mm, the mean TDs were 26.92 mm and 25.45 mm in males and females, respectively, with a statistically significant difference between the sexes. Similarly, in a study by Cirpan et al. on 150 dry skulls, found that the mean AP and TDs were 34.38 mm and 28.95 mm, respectively.
In a study by A. Metin Tellioglu et al. on measurements obtained from 3D-CT images of 100 patients (50 males and 50 females), the mean AP diameter was 34.73 ± 2.21 mm, TD was 30.47 ± 2.25 mm, circumference was 119.82 ± 10.23 mm and area was 8.17± ±1.09 mm2 in males and in females, the mean AP diameter was 32.99 ± 2.65 mm, TD was 28.4 ± 2.72 mm, circumference was 113.08 ± 9.09 mm and area was 7.27 ± 0.9 cm2 with all the variables showing statistically significant difference between the sexes.
In a study by Galdames et al., analyzing the AP and TD of the foramen magnum in a Brazilian sample, concluded that these parameters should be used with caution due to the lower accuracy.
In our study, the results of all the variables investigated displayed statistically significant differences (P < 0.01) between the sexes. The mean AP diameter was 36.89 mm, TD was 32.47 mm and the area was 9.15 cm2 in males, while in females, the mean AP diameter was 34.91 mm, TD was 31.11 mm, and the area was 8.97 cm2 [Table 2].
Population differences have an important role in defining sexual dimorphism in the cranium. [Table 7] describes the variables of the foramen magnum of the Kashmiri population with that of Turkish, British, Iraqi, and Indian population. Therefore, it is necessary to know the source population of any unidentified skeletal remains to choose a method based on data from that particular population or a population with similar expression of sexual dimorphism.
Interestingly, the prediction percentages for a combination of foramen magnum variables from our study show similar levels of prediction when compared to studies of other populations. Gabert et al. in his study on skeletons from the 18th and 19th century found sex determination accuracy of 68.8% with univariate functions and 70.3% with multivariate functions from the foramen magnum. According to the study conducted by Raghavendra Babu et al. on dry skulls of Indian population, found that the sex estimation rate with TD was 65.4%, with AP diameter was 86.5% and with different formulation of area the estimation rate was as high as 81.6% and 82.2%. However, according to the Kamath et al., the sex estimation rate was 70.3% using area measurement. Uthman et al. in a study on foramen magnum measurements through CT images, revealed that the best discriminant parameters were foramen magnum area and circumference measurements with accuracy rates of 69.3% and 67%, respectively.
In our study, the most reliable variable was AP diameter with 70% sex differentiation using univariate discrimination function for all groups. The most reliable discriminant variable for males was TD (64%) and for females was AP diameter (78%).
Routal et al. had claimed an accuracy of up to 100% in predicting gender from the foramen magnum, while Holland et al. scored an accuracy of 71% to 90% in the main sample and 70-85% in the control group by using regression equations in place of discriminant functional analysis.
Our study showed that sex determination can be obtained from the measurements of the foramen magnum similar to other regions of the skeleton and cranium. As sexual dimorphism from the foramen magnum is population based and ethnic differences, our study would contribute in sex estimation of the Kashmiri population. There are many other regions within the cranium besides the foramen magnum that have been used for determination of the sex of an individual like mastoid triangle, paranasal sinuses, etc.
| Conclusion|| |
The estimation of sexual dimorphism using foramen magnum region of the skull has revealed significant difference between the sexes and therefore, be considered useful in the identification of sex of an individual particularly in mass disasters. The data from our study would contribute to the literature on the determination of the sex of individuals and also provide guidance on the usefulness of CT scan in the forensic and anthropological studies. Our study can be used to supplement other sexing evidence available so as to precisely ascertain the sex of the skeleton.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]