INCIDENCE OF TYPES OF PTERION IN SOUTH INDIANS – A STUDY ON CADAVERIC DRY SKULLS

Address for Correspondence: Dr. Channabasanagouda (MBBS MD), Associate Professor, Department of Anatomy, Koppal Instistute of Medical Sciences, Koppal, Karnataka – 583231 Phone : 09481562274 E-Mail: drcbg2007@gmail.com Introduction : Pterion is an important landmark in the temporal fossa. It is a significant area for the surface location of anterior branch of middle meningeal artery and stem of lateral sulcus of the cerebrum. Based upon the pattern of articulation of the bones, different varieties of pterion have been encountered. Knowing about the incidence of types of pterion is very important for neurosurgeons, anthropologists, forensic scientists and radiologists. Materials and methods : Current study was done on 282 dry adult human cadaveric skulls (564 sides), for the incidence of different types of pterion. Types of pterion are – sphenoparietal type, frontotemporal type, stellate type and epipteric type. Results : Out of the 564 pteria,we have identified 455 sphenoparietal type, 77 frontotemporal type, 17 stellate type and 15 epipteric types. The incidence of different types of pteria have been correlated and compared with the data available from previous studies. Conclusion : The current study on incidence of types of pterion will add further knowledge to the available data about types of pterion and it will be of immense help for neurosurgeons, orthopedic surgeons, pediatricians, radiologists and anthropologists for proper diagnostic and therapeutic purposes.

has classified the pterion into three types, sphenoparietal type (sphenoid and parietal bones articulate directly), frontotemporal type (frontal and temporal bones articulate) and stellate variety (all the four bones meet at a common point).Murphy [5] added fourth type to the existing three types, which is named as epipteric type, where there will be presence of a sutural bone at the pterion.Two more types were added by Wang [6] these are zygomaticotemporal and zygomaticoparietal types, where the zygomatic bone articulates with temporal and parietal bones respectively.Being an important landmark for the neurosurgeons, pterion has acquired interest by anthropologists and forensic science experts, as there is variation in its pattern in different population groups [7].The area of pterion is weak, as the bones here are considerably thin.Thus making the pterion vulnerable for fracture.A blunt trauma here may rupture anterior division of middle meningeal artery, resulting in an extradural hematoma [8].Pterion is important as a craniometric landmark for the location of anterior branch of middle meningeal artery, Broca's area, insula and stem of lateral sulcus.
It is a primary area to gain access to sphenoid ridge and the optic canal [9].Though the pattern of pterion is classically described as an H shaped suture, it is subjected for variant presentations.Knowing the pattern of pterion is of significance for surgical approaches to the underlying structures.This study, on dry adult human skulls adds to the available information about the types of pterion.Further, presence of a sutural bone at the pterion, may complicate neurosurgical and radiological procedures.Thus the current study is significant for neurosurgeons, radiologists, anthropologists and forensic science experts.

MATERIALS AND METHODS
564 sides of 282 dry adult human skulls, irrespective of sex have been studied for the sutural morphology of the pterion.Out of the 564 pteria, 455 were sphenoparietal type, 77 were frontotemporal type, 17 were stellate type and 15 were epipteric type.The incidence of different types of pterion has been correlated and mentioned in the following table.skulls.We have observed 80.53% of sphenoparietal variety of pterion in 282 skulls (564 sides), accounting for the highest incidence in our study.Right sided sphenoparietal accounted for a slightly more incidence than the left sided one.

OBSERVATIONS
Following table shows the comparison between the incidences of types of pterion in different population groups.
The pterion has its own surgical significance, for being an important landmark for locating various intracranial structures.Thus, knowing the pattern/types of pterion is of considerable significance.Previously studies have been done, classifying the pterion into three types [4], four types [5] and six types [6].
The sphenoparietal type is the most common type of pterion reported by many authors in their studies in different population groups.Seema [7] observed 94% of sphenoparietal type, 3% of stellate type, 2% epipteric and 1% frontotemporal type of pteria, in a study on South Indian and Zalawadia [11] also reported that the incidence of sphenoparietal type is more than 90%.In our study, we have identified 80.53% of sphenoparietal type of pterion, which is similar to majority of the studies, especially those studies on Indian skulls.have caused morphological changes in the calvaria, due to which greater wing of sphenoid met with the parietal bone [17].
We have observed 13.62% of frontotemporal type and 3.09% of stellate variety of pteria.The frontotemporal variety was slightly more on left side, where as stellate type were slightly more on right side.Saxena [9] reported 10.11% of frontotemporal and 5.06% of stellate types of pteria in Nigerans.Pavan [15] reported 16.4% 8.8% of frontotemporal and stellate types respectively in a study on South Indian skulls.Manjunath [10] observed 3.52% of frontotemporal type, which is a slightly less incidence compared to other studies.In many of the population groups, frontotemporal type is the second most common type, followed by stellate type.But in a study by Murphy [5] stellate type was the second most common type (18.5%), followed by the frontotemporal type (7.5%).Variations in pteria may be due to the result of combination of genetic and environmental factors [5].Wang [6] did a study on sutural pattern of rhesus monkeys and concluded that the variations show familial aggregation and are likely to be regulated by genes.When a sutural bone is present at the pterion, it is called as epipteric type of pterion.Manjunath [10] reported 17.3% of epipteric type and Nair [13] reported 4.8% of epipteric type.Both these studies are on South Indian skulls.Saxena [9] in his study on Nigerian and Indian skulls, did not find any epiptric type of pterion.In our study, incidence of epipteric type of pterion is 2.62%, which is the least among the four varieties of pteria.Among the epipteric type of pteria observed, majority were right sided.Results of our study are almost similar those by Hariprasad [14] and Pavan [15].Differences in the incidence of types of pteria may be due to the racial characters of various populations.Sutural bones or wormian bones are small irregular bones, developed due to accessory ossification centres, found along sagittal and lambdoid sutures and at the pterion, lambda and asterion.Some authors opined that the presence of epipteric/wormian bones may be genetic or it may be associated with malformations of the skull and central nervous system anomalies [18,19].
Presence of epipteric bones may give false impression of fractures or fractures may be interpreted for wormian bones, radilogically or clinically, more so when they are at the pterion [20].Presence of wormian bones at the pterion, may complicate the neurosurgical procedures, like making burr holes [21].

CONCLUSION
We report 80.53% of sphenoparietal type of pterion, which is highest and 2.62% of epipteric type of pterion, which is lowest.Pterion is an important landmark for approaching the cranial cavity.It is one of the standard approach by the neurosurgeons for the lesions in the anterior and middle cranial fossa.A prior knowledge of variants of pterion is significant for pterional approach, especially when a burr hole is planned at this location.The incidence of different types of pterion are of particular interest to anthropologsists, forensic scientists, neurosurg-eons and radiologists.The data displayed by our study, adds on to the previous studies, with comparison between the population groups.Though genetic and racial causes have been implicated in the variation of sutural pattern of pterion, there is a need of further study on correlation between sutural configuration and growth of brain.This data also provides an information for evaluating the causes of variations in pterion and evolution of morphology of pterion.
Authors are thankful to the Miss Anuradha R for her contribution in this study and also the previous authors from whom we have collected the data.

INTRODUCTION
International Journal of Anatomy and Research, Int J Anat Res 2017, Vol 5(3.2):4290-94.ISSN 2321-4287 DOI: https://dx.doi.org/10.16965/ijar.2017.313Anteroinferior angle of parietal bone (sphenoid angle), is the meeting place of four bones, with an H shaped suture.Bones which meet here are the squamous part of frontal bone, greater wing of sphenoid bone, anteroinferior angle of parietal bone and the squamous part of temporal bone.This region is called as the pterion.Centre of the pterion is an important landmark for the surgeons, lies about 4cm above the The pterion represents the junction of the frontal, sphenoid, parietal and temporal sutures within the temporal fossa.It marks the position of the frontal branch of middle meningeal artery.Pterion is an important anthropometric landmark.It corresponds to the site of anterolateral fontanelle of the neonatal skull, which closes in the third month after birth [1].zygomatic arch and 3.5cm behind the frontozy gomatic suture [2].It is a clinically important area of bone junctions.In greek, pterion means wing.Usually sphenoid and parietal bones meet at the pterion.Less commonly frontal and temporal bones articulate, sometimes all four bones meet at a point [3].Pterion has got a considerable importance in age and sex determination.It is an important landmark for the location of anterior division of middle meningeal artery, Broca's area and sphenoid ridge [4].There are various types of pterion depending on the meeting pattern of the bones.Accordingly,
Many authors have opined reasons behind the greater incidence of sphenoparietal type.As per Ashley-Montague [17], sphenoparietal variety of pterion is common in human beings but frontotemporal type is dominant in non-human primates.During evolution, anterosuperior segment of squamous part of temporal bone got detached from it, incorporated into the greater wing of sphenoid, so as to bring about a change from frontotemporal to sphenoparietal type [17].It is an evolutionary basis and has been shown that growth of bones of calvaria is in coordination with growth of brain and needs an interaction between different tissues in the suture [16].Increase in brain size in human beings would Manjunath Halagatti, Channabasanagouda.INCIDENCE OF TYPES OF PTERION IN SOUTH INDIANS -A STUDY ON CADAVERIC DRY SKULLS.

Table 1 :
Incidence of different types of pteria.

Table 2 :
Comparison of incidence of types of pterion in different population groups.
Murphy [4], who has classified the pterion into four different types, reported 73% of sphenoparietal type of pterion in Australians.Saxena 9 did a study on Nigerian and Indian skulls and reported 84.79% and 95.3% of sphenoparietal type in respective populations.Manjunath [10]