Introduction

Pterion is a point of irregular H-shaped sutural confluence seen in the norma lateralis of skull, formed by the frontal, parietal, temporal and sphenoid bones. Pterion corresponds to the site of the antero-lateral fontanelle of the neonatal skull, which closes in the third month after birth.1

It is also known as the sylvian point. Fronto-zygomatic suture and midpoint of zygoma can reliably be used in locating pterion. It is located 4cms above midpoint of zygomatic arch and 3.5cms behind fronto-zygomatic suture.2 Pterion receives its name from the greek word “Pteron”, meaning wing. In greek mythology, Hermes, messenger of the gods, was enabled to fly by winged sandals, and wings on his head which were attached at the pterion.

One or more sutural bones appear between the sphenoidal angle of the parietal and the greater wing of the sphenoid known as pterion ossicles or epipteric bones,2 these sutural bones may be mistaken radiologically for fracture of the skull in the pterion region.3

Pterion is an important landmark for anterior branch of middle meningeal artery, broca’s motor speech area to the left, insula, lateral cerebral fissure, for the pathologies of optic nerve, orbit, sphenoid ridge and for the anterior circulation aneurysms and tumors.4

Objectives of the Study

Materials and Methods

The present study was conducted on 100 adult human skulls collected from the department of Anatomy and Forensic Medicine at Kempegowda Institute of Medical Sciences and from other Medical and Dental colleges in and around Bengaluru.

It is an observational study. All human skulls (irrespective of sex) with intact calvaria, well defined sutures and erupted third molar teeth are considered for study. Damaged skulls, old skulls with obliterated sutures and skulls of newborn, infants and children are excluded

Skulls were observed macroscopically with the naked eye for sutural pattern. Skulls are classified based on Murphy’s classification.

Findings of sutural pattern of pterion were noted. Values were recorded separately on right and left sides and compared. Values were also compared with previous studies for their statistical significance.

Results

In the present study, Sphenoparietal was found to be commonest (78%). Frontotemporal was seen in 02%, Stellate type was observed in 04% and epipteric type was seen in 16% of cases. In two skulls, ‘two’ epipteric bones were noticed. The same type of pterion occurred on both right and left sides in the same individual in 75% of the cases. SP type occurred more bilaterally where as FT, stellate and epipteric types occurred more unilaterally shown in Table 1. In the present study, sphenoparietal and stellate occurred more on right side whereas frontotemporal and epipteric types occurred more on left side shown in Table 2. Two sutural bones at pterional site were noted in two skulls, one on right side and other on left side.(Figure 3)

Figure 1

Epipteric type of pterion

Figure 2

Fronto-temporal type of pterion

Figure 3

Pterion with two epipteric bones

Figure 4

Stellate type of pterion

Figure 5

Speno-parietal type of pterion

Discussion

In the present study the occurrence of SP type was 78% which is high when compared to Hussain Saheb et al., Mwachaka P.M et al. and Oguzetal studies. The high occurrence of SP type could have an evolutionary basis. The SP type of pterion is the dominant form in humans whereas the fronto-temporal type is dominant in non-human primates. In primate evolution, the antero-superior segment of the squamous part of the temporal bone of lower primates become detached from its parent and gets incorporated into the postero-superior angle of the greater wing of the sphenoid bone of humans, thereby changing the pterion pattern from the fronto-temporal type of non-human primates to the spheno-parietal type of humans. Frontotemporal type is least commonly seen in the present study. This is similar to Ankur Zalwadia et al. study but low when compared to Oguzetal, Mwachaka P.M et al. and Hussain Saheb et al. studies. The occurrence of fronto-temporal pterion in man is considered to be atavism due to a natural reversion of a stage in the phylogenetic development of man in which the fronto-temporal type was the normal and constant.

From the present study it was seen that the same type of pterion occurs more bilaterally than unilaterally. This is in agreement with the findings among kenyans but differs with that among turks, where the occurrence of pterionic type varied significantly on the left and right sides. These differences could be due to the different sample sizes used in the study. In the present study, sphenoparietal type was the predominant type. This is in agreement with other studies.

Present study has shown that the same type of pterion occurs more bilaterally than unilaterally. This is in agreement with Wandee C et al., Mwachaka PM et al. and Ankur Zalwadia et al.

Conclusion

Spheno-parietal was the most common type observed. Bilateral presentation of this type is more common when compared to unilateral presentation. This type of pterion was present more on right side than left side. Fronto-Temporal was least commonly observed. This type was seen unilaterally only. It was seen more on left side. In Stellate type unilateral presentations were more common than bilateral presentation. This was seen more on right side. Epipteric type was the second most common type observed. This type was seen more commonly on left side. Asymmetrical presentation was more common than symmetrical presentation. The present study has shown no significant side difference for the types of pterion. Is useful for anthropologists, forensic pathologists, neurosurgeons and maxillofacial surgeons.

Source of Funding

None.

Conflict of Interest

The author declares no conflict of interest.