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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 4  |  Issue : 3  |  Page : 150-155

Sexual dimorphism of foramen magnum between two different groups of Indian population: A cross-sectional cone-beam computed tomography study


Department of Oral Medicine and Radiology, Subharti Dental College, Meerut, Uttar Pradesh, India

Date of Web Publication28-Sep-2018

Correspondence Address:
Dr. S M Ravi Prakash
Department of Oral Medicine and Radiology, Subharti Dental College, Swami Vivekanand Subharti University, New Delhi Haridwar Bypass Road, Meerut - 250 002, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jfsm.jfsm_19_18

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  Abstract 


The foramen magnum (FM), being a vital landmark at the base of the skull, includes interests to many fields of medicine. Many authors have recounted the usefulness of the FM in gender determination. The emphasis of this study is to evaluate the shape and dimensions of the FM among males and females and to establish its role in sexual dimorphism using cone-beam computed tomography (CBCT). Furthermore, to evaluate the area and FM index (FMI) among males and females and finally to evaluate the differences in FM measurements if any in two different regions of an Indian population. One hundred and ten CBCT scans (55 males and 55 females; age range, 20–80 years) were selected for this study. The sagittal diameter, transverse diameter, area, FMI, and circumference of FM were measured, and data were subjected to discriminant analysis for the evaluation of sexual dimorphism. The area of FM was the best discriminant parameter which was used to study the sexual dimorphism with an overall accuracy of 90.9%. It can be concluded that the reconstructed CBCT image provides valuable measurements for the FM and could be used for gender determination.

Keywords: Craniometry, dimorphism, foramen magnum


How to cite this article:
Gargi V, Prakash S M, Malik S, Nagaraju K, Goel S, Gupta S. Sexual dimorphism of foramen magnum between two different groups of Indian population: A cross-sectional cone-beam computed tomography study. J Forensic Sci Med 2018;4:150-5

How to cite this URL:
Gargi V, Prakash S M, Malik S, Nagaraju K, Goel S, Gupta S. Sexual dimorphism of foramen magnum between two different groups of Indian population: A cross-sectional cone-beam computed tomography study. J Forensic Sci Med [serial online] 2018 [cited 2018 Dec 17];4:150-5. Available from: http://www.jfsmonline.com/text.asp?2018/4/3/150/242510




  Background Top


A man is born with an identity and deserves to die with the same. However, at number of instances, such as natural calamities, mass disasters, and intentional/unintentional act of fellow human beings bring forth unidentified bodies.[1] Unidentified skeletal remains often cause problems in gender determination and the investigating team, or the forensic experts have to face challenge in these circumstances.[2] In biological profiling of unidentified human remains, sexual dimorphism found in the skeletal system has its own magnitude. Gender is usually understood more accurately, the more complete the set of human remains (bones) what are available.[3] The second best sexually dimorphic portion of the body after the pelvis is the skull.[4] The craniofacial structures have the advantage of being composed largely of hard tissue, which is relatively indestructible such as the mastoid, foramen magnum (FM) and the occipital condyles.[5] The basal region of the occipital bone is likely to survive the physical insults than the other parts of the skull because of the abundant soft-tissue cover, skull thickness in the region, and anatomical position which is relatively well protected, thus preserving it for forensic evaluation.[6] Significant differences exist in the measurements of FM between males and females in different geographical regions.[7] The FM is an important landmark of the skull base and is of important interest in anthropology, anatomy, forensic medicine, and other medical fields. It is a three-dimensional (3D) circular or oval aperture within the occipital bone centrally. FM transmits the medulla oblongata and its membranes. Other structures that pass through FM are spinal accessory nerve and vertebral arteries. In clinical forensic medicine, use of radiographs is noteworthy and widely accepted. They are acquired as a part of postmortem investigations to detect foreign bodies or document fractures or other injuries.[8] Cone-beam computed tomography (CBCT) is an emerging modality in the present scenario and is better in terms of less exposure, less scan time required, 1:1 ratio of the scanned structure, and also cost-effective.

The present study aims to provide data on FM for the purpose of gender determination and comparison between the two different regions of an Indian population.


  Materials and Methods Top


The study was conducted in Subharti Dental College, Meerut, Uttar Pradesh, and the studied sample comprised 110 patients who were divided into two main groups (55 adults were from Uttar Pradesh population and 55 adults were from Northeastern parts of India; age range 20–60 years). Patients who were subjected to CBCT for dental implant surgery, tumors, cysts, embedded teeth, etc., in our dental hospital were enrolled in the study. The study protocol was approved by the Institutional ethical committee. The study was designed to measure the dimensions of FM for sexual dimorphism using CBCT. The research was performed in accordance with the Declaration of Helsinki principles.[9] Written consent was also obtained from each patient in the study before exposure. Patients with a fracture or pathology in the region of the FM were not included in the study. Digital image was taken from CBCT Scanner (Sirona GALILEOS comfort CBCT scanner [Sirona Dental System GmbH, D 64625 Bensheim, Germany] with the effective radiation dose of 68–1073 μSv). The orientation of the images was made for each patient before the measurements. For the FM measurements on the sagittal view, a line passing from the anterior to posterior border of the FM was oriented parallel to the horizontal plane. The FM sagittal diameter (FMSD) was recorded as the greatest anteroposterior dimension of the FM and the FM transverse diameter (FMTD) was recorded as the greatest width of the FM. The FM circumference (FMC) was measured after tracing the bony margin of the FM on the CBCT image [Figure 1]. FM index (FMI) was calculated using following formula:
Figure 1: The foramen magnum circumference, foramen magnum transverse diameter, and foramen magnum sagittal diameter was measured on the cone-beam computed tomography image

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FMI = FMTD × 100/FMSD

The FMI was evaluated using Martin and Saller classification:[10]

  1. Narrow: X–≤81.9
  2. Medium: 82.0–85.9
  3. Large: ≤86.0–X.


FM area (FMA) was calculated from FMTD and FMSD utilizing different formulae given by Routal and Teixeira:

Formula given by Teixaria: Area = π ([FMSD + FMTD)/4][2]

Formula given by Routal: Area = FMSD × FMTD × π/4

Data were analyzed using the Statistical Package for the Social Sciences 17.0 software for Windows. During the evaluation of the study data, along with the descriptive statistical methods, parameters with normal distribution for the comparison of quantitative data were evaluated using one-way ANOVA, Student's t-test, and discriminant analysis with “the stepwise feature being used to choose the most discriminatory variables” and inferences were drawn. P < 0.001 was considered to be highly significant.


  Results Top


Age

Out of 110 patients, the overall mean age of the studied population was 33.82 ± 9.53 years (age range-18–80 years). The sample was divided into age groups, and there was no statistically significant difference found between age groups and measurements of FM in both males and females (P > 0.05) [Table 1] and [Table 2].
Table 1: According to age groups the FM measurements in males

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Table 2: According to age groups the FM measurements in females

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Gender

  • As shown in [Table 3], mean FMSD in male and female was 34.84 ± 1.83 (range 31.38–40.01) and 32.96 ± 2.21 (range 28.56–37.13), respectively. The difference was statistically significant (P = 0.000). Mean FMTD in males and females was 30.65 ± 1.79 (range 26.21–33.89) and 28.7 ± 1.91 (range 26.15–34.25). In addition, the mean circumference of FM in males and females was 106.28 ± 3.718 (range 95.38–112.05) and 99.463 ± 3.7 (range 90.11–109.39). There was highly significant difference in mean FMTD and circumference between males and females (P = 0.000)
  • Mean FMI was 88.17 ± 6.33 (range 66.04–99.97) for males and 88.085 ± 5.79 (range 74.98–102.57) for females. The result showed large type of FMI according to Martin and Saller classification. There was no significant difference in mean FMI between males and females was found (P = 0.941)
  • The mean area of FM calculated by Teixeira formula for males and females was 844.2 ± 69.78 (range719.45–1023.10) and 756.07 ± 88.66 (range 592.04–981.01). The mean area of FM calculated by Routal formula for males and females was 839.6 ± 69.79 (range 717.13–1011.00) and 752.12 ± 88.31 (range 591.07–978.48). The mean area calculated by both the formulae showed statistically significant difference (P = 0.000).
Table 3: The mean values of measurements of foramen magnum according to gender

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Shapes

Round shape and hexagonal shape was the most common type in the skull bones of males and females, respectively [Table 4] and [Graph 1].
Table 4: The percentage of various shapes of the foramen magnum of both genders

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The overall mean value for transverse length, sagittal length, circumference, and FMI was 29.81 ± 2.03, 33.90 ± 2.23, 102.87 ± 5.03, and 88.12 ± 6.04, respectively. The overall area calculated by Teixeria formula and Routal formula was 800.13 ± 90.92 and 795.87 ± 90.60, respectively [Table 5]. While comparing the mean values of morphometric measurements of FM in males between the North Indian and Northeastern population, the mean value for FMC and FMSD was moderately significant, while mean value for FMI was highly significant [Table 6]. The mean value for FMA and FMSD were found to be moderately significant between North-Indian and North-Eastern females [Table 7].
Table 5: Overall mean value for morphometric measurements of foramen magnum

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Table 6: Comparison of mean values of FM amongst ethnic groups in males

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Table 7: Comparison of mean values of FM amongst ethnic groups in females

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According to the results, circumference and transverse length of FM served as a final predictor of gender. It could correctly identify males in 83.6% and females in 90.9% of the cases [Table 8], and the overall predictive accuracy was found to be 90.9%.
Table 8: Classification for males and females using stepwise discriminant analysis for FM

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  Discussion Top


One of the critical ways to form a comprehensive base on gender determination in medicolegal cases is skull morphometry. The skull, pelvis, and femora are the most suitable for radiological determination of gender. When the skeleton exists wholly, gender can be determined with 100% precision in contrast to cases of explosions, warfares, and other mass disasters. In the aforementioned scenario, radiography can assist in giving precise dimensions after applying specific formulae to determine the gender.[10] Gender determination can be accomplished using either morphological or morphometric methodologies. In our study, the overall mean age of the studied population was 33.82 ± 9.53 years (Age range-18–80 years). In a study done by İlgüy et al.,[11] the mean age of the studied group was 45.66 ± 16.95 years which was slightly higher than the present study which may be due to difference in the population group.

Catalina-Herrera,[12] Uysal et al.,[13] Uthman et al.,[3] Radhakrishna et al.,[14] Jain et al.,[15] and Patel and Mehta [16] studied the measurements of the FM using different metric means for instance direct measurement on skull base, radiographs, or CT scans and found that the FM shows sexual dimorphism. Several studies which are done by Kanchan et al.[17] and Shepur et al.[18] have stated that the FM does not show sexual dimorphism.

Our findings were similar with the results reported on the British sample [19] as well as on Indian populations [1],[14],[20] where statistically significant differences between males and females for FMSD, FMTD, and FMA has been shown. In addition, our study showed statistically significant differences in the mean value of circumference between males and females which was found to be moderately significant in the study done by Jaitley et al. 2016.[1]

Uysal et al.[13] did a study using 3D CT and took seven measurements of the FM on 3D. FM diameters were found to be statistically different in each sex (P = 0.001), with a sex determination accuracy rate of 81% in accordance to our study where the overall predictive accuracy found to be 83.6%.

Deshmukh and Devershi [21] studied that gender determination can be done from the cranium and they found that 32.4% of crania was sexed correctly. Tambawala et al.[22] used the FM dimensions and got the overall accuracy rate for sex determination to be 66.4%. Out of these, 70.3% of males and 62.6% of females were sexed correctly. The best parameter for sex determination according to their study was the area of the FM. In addition, the accuracy rate of sex prediction using the area dimensions (Teixeira's formula) was 66.4%, same as that of all the four FM parameters used together. Their result was in consistency with our study.

Erdil et al.[23] did a study on morphometric analysis of the FM by CT, the mean age of the 54 patients was found to be 43.63 ± 21.28 years, which is slightly higher than found in our study, but FMTD 29.84 ± 2.90 mm, FMSD 35.58 ± 4.11 mm, and FMI 84.36 ± 8.40 corresponded well with the findings of our study. The average value of FMI in the human skull obtained by Howale et al.[24] and Chaturvedi and Harneja [25] was 84.85 ± 4.77 and 83.81, respectively, which was also in accordance with our study.

Murshed et al.[26] reported the mean value of the FMSD (34.6 ± 3.16 mm in females and 37.2 ± 3.43 mm in males) and the FMTD (29.3 ± 2.19 mm in females and 31.6 ± 2.99 mm in males). In the present study, value of FMSD and FMTD was close to the results reported in Murshed et al.'s study.

On the subject of FMC, Uthman et al.[3] reported the measurement as 92.6 ± 6.5 mm for females and 99.3 ± 6.2 mm for males which were lower than the ones recorded in the present study. These differences might be due to the difference between the anatomic and radiographic methods.[12] reports the mean value of FMC to be 102.2 ± 6.8 for females and108.1 ± 7.1 for males. These results are in accordance with our present study. It was noticeable that the mean values of FMSD, FMTD, and FMC in males were significantly higher than in females among all studies carried out on the FM. Similarly, the values of males were higher than females in the present study [Table 2], P < 0.01].

There was no significant difference in FMI between males and females in the present study which corresponds well to the study done by Subhangi et al.[27]

In our study, we have classified the FM into eight shapes based on the study by Govsa et al.[28] and Chethan et al.[29] have found 7.93% and 15.1% oval shaped in their studies, respectively, which is much lower than our finding. A study done by Chetan et al.[29] observed round shape to be the most common type which is consistent with the present study. In a study done by Raikar et al.,[30] the most common shape of FM observed was egg shape followed by round shape, but the incidence rate of round shape in their study (26%) is almost similar to the incidence rate in our study. Vinutha and Shubha [31] studied 200 skull samples and found that oval shape was the most common and pentagonal type was the least common type of FM shape in both the genders, in contrast to the present study where round shape was most common among males and hexagonal shape was most common among females.


  Conclusion Top


FM measurements are valuable in studying sexual dimorphism in forensic investigations. FM dimensions tend to stabilize after the second decade of life, and the CBCT images can provide reliable measurement of these dimensions. It was noted that significantly higher mean value of length, breadth, circumference, and area of FM were present in males than females. Future studies may include larger numbers of participants from various ethnic backgrounds to form a more circumspect data so that skulls from different populations can be assigned sex more accurately. The FM measurements of living persons may serve as a database that may be useful for sex identification. Additional studies on a larger number of cases are needed due to the variation which might be present between different populations which may affect the bone measurements.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Uysal S, Gokharman D, Kacar M, Tuncbilek I, Kosa U. Estimation of sex by 3D CT measurements of the foramen magnum. J Forensic Sci 2005;50:1310-4.  Back to cited text no. 13
    
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    Figures

  [Figure 1]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]



 

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