Morphometric Analysis and Variation of Pterion, Asterion and Lambda in Dry Human Skulls and Its Sexual Dimorphism

Introduction: Pterion is a Hshaped sutural junction of the frontal, parietal, squamous part of the temporal and greater wing of sphenoid bone. Asterion is a sutural junction of lambdoid, parietomastoid and occipitomastoid sutures. Lambda is the junction where lambdoid sutures and sagittal sutures meet. These sutures play an important role in infants' brain development. Flexibility of these allows the bones to overlap and hence it can pass through the brain canal easily without any damage to the brain. Aim: To analyse pterion asterion and lambda of dry human skulls morphologically and morphometrically and determine its sexual dimorphism. Materials and Methods: 40 dry human skulls were collected from the department of Anatomy of Saveetha dental college and hospitals. By excluding abnormal and damaged skulls, 20 skulls were studied. Out of 20 skulls, 11 were male skulls and 9 were female skulls. On investigation, Pterion was classified into four types: Sphenoparietal, stellate, Epipteric and Frontotemporal. Asterion was classified into types: Type-1 and Type-2 based on the presence and absence of wormian bones respectively. Lamda was classified into two types: Normal and Abnormal. Statistical analysis was done by SPSS software. Paired Sample T test was used to analyse the data. Original Research Article Karunakaran and Mohanraj; JPRI, 33(60B): 1218-1226, 2021; Article no.JPRI.78876 1219 Results: Percentage of occurrence of different types of pterion in males and females: Sphenoparietal (59.09 % of males and 59.09 % of females), Stellate (27.7% of males and 22.2% of females), Epipteric (99% of males and 16.6% of females) and Frontotemporal (45.5% of males and 5.5% of females). Different types of Asterion: Type-1 (13.63% of males and 16.66 % of females and Type -2 (86.63% of males and 83.33% of females). Different types of Lambda: Normal (90.9% of males and 94.4% of females), Abnormal (9% of males and 5.55% of females). Conclusion: In the present study, there was no correlation between the male and female skulls in the presence of Pterion, Asterion and Lambda. Therefore these cannot be used as reliable parameters for determining sexual dimorphism.


INTRODUCTION
Pterion is a H-shaped sutural junction of the frontal, parietal, squamous part of the temporal and greater wing of sphenoid bone. Pterion is also referred to as "Anterolateral fontanelle" in infants. It closes 2-3 months after birth. Sutural bone present in the pterion region is called "Pterion ossicle" or "Epipteric bones". Pterion is a fragile point that could be fractured easily because the calvarias wall is thin. Pterion overlies the anterior branch of the middle meningeal artery and lateral fissure of the cerebral hemisphere. Hence, damage to this point might lead to extradural hematoma [1]. The anatomical position of the pterion is important for surgical management of extradural hemorrhage, brain tumors, aneurysms located in the anterior and middle cranial fossae [2][3][4][5].
Asterion is the junction of the mastoid part of temporal, parietal and occipital bones. It serves as an important surgical landmark for the posterior cranial fossa, corresponding to the location of the transverse sinus and is also a surface landmark for anthropological and radiological measurements of the skull [6][7][8]. Asterion is referred to as "Posterolateral fontanelle" in infants. It closes at 12 months after birth.

MATERIALS AND METHODS
40 dry human skulls were collected from the Department of Anatomy of Saveetha dental college and hospitals, Chennai. By excluding abnormal and broken skulls, 20 skulls were selected for this study. 20 skulls were classified as skulls, 11 male skulls and 9 female skulls using various parameters. On investigation, Pterion was classified into four types: Sphenoparietal, stellate, Epipteric and Frontotemporal [30]. Asterion was classified into types: Type-1 and Type-2 based on the presence and absence of wormian bones respectively [31]. Lambda was classified into two types: Normal and Abnormal. Statistical analysis was done using SPSS software version 23.0. Paired Sample T test was used to analyse the data.

RESULTS AND DISCUSSION
Male skulls were 11 and female skulls were 9, out of 20 skulls analyzed. From the obtained data the percentage was calculated for comparison between male and female. Percentage of occurrence of different types of pterion in males and females: Sphenoparietal (59.09 % of males and 59.09 % of females), Stellate (27.7% of males and 22.2% of females), Epipteric (99% of males and 16.6% of females) and Frontotemporal (45.5% of males and 5.5% of females). Different types of Asterion: Type-1 (13.63% of males and 16.66 % of females and Type -2 (86.63% of males and 83.33% of females). Different types of Lambda: Normal (90.9% of males and 94.4% of females), Abnormal (9% of males and 5.55% of females).

Discussion
In the study done by Natis K et al., [32], 90 skulls were selected and on investigation, pterion were classified into four types and the percentages of occurrence of each type of pterion was obtained: Sphenoparietal (58%), Stellate (25%), Epipteric (15.5%) and Frontotemporal (1.1 %) and no sexual dimorphism was determined. In the present study, the occurrence percentage obtained for Sphenoparietal was 59.09% of males and 55.55% of females, Stellate was 27.27% of males and 22.2% of females, Epipteric was 9% of males and 16.6% of females and Frontotemporal was 4.5% of males and 5.5% of females. The percentage of types of pterion between male and female is shown in Table 1.  [34,35], 302 skulls were selected and on investigation lambda was classified into two types percentage of occurence of each type of lambda was obtained: normal lambda (92.7% of males and 96.1% of females ) and abnormal lambda (7.3% of males and 3.9% of females). The percentage of types of lambda between male and female is shown in Table 3.  In the present study, the occurrence percentage obtained for normal lambda was 90.9% of males and 94.4% of females and for abnormal lambda 9.09% of males and 5,55% of females.
The anatomical location of the presence of pterion, asterion and lambda are necessary for the surgical management of the region concerned and the brain areas involved. The variations in the presence or morphological alterations can provide a clue for the neurosurgeons to take precautions on the changes that occurred and can implement their altered surgical approach if needed. The variations between the male and female skulls with asterion, pterion and lambda shape and presence can also be very much useful in the neurosurgical approaches between the genders creating anatomical knowledge on these structures concerned.

CONCLUSION
In the present study, there was no correlation between male and female skulls with asterion, pterion and lambda. Therefore these are not reliable parameters for determining sexual dimorphism.

LIMITATIONS
The present study is inconsistent due to less number of skulls available .The study was conducted and completed in a short span of time.

FUTURE SCOPE
Further studies can be done with more number of skulls in order to obtain significant results and to get a clear idea about the subject.

CONSENT
It is not applicable.

ETHICAL APPROVAL
As per international standard or university standard written ethical approval has been collected and preserved by the author(s).