A MORPHOMETRIC STUDY ON DIFFERENT SHAPES OF PTERION AND ITS CLINICAL SIGNIFICANCE ABSTRACT

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1 Original Research Article Anatomy International Journal of Pharma and Bio Sciences ISSN A MORPHOMETRIC STUDY ON DIFFERENT SHAPES OF PTERION AND ITS CLINICAL SIGNIFICANCE YUVARAJ.M 1 *, PUSHKARAN.J 2 SANKARAN P K 1, PRIYADARSHINI 1 AND GUNAPRIYA RAGHUNATH 1 1 Department of Anatomy, Saveetha Medical College and Hospital, Chennai, Tamilnadu, India 2 Department of Neuro surgery, Saveetha Medical College and Hospital, Chennai, Tamilnadu, India ABSTRACT Pterion is a H- shaped sutural confluence seen in the Norma Lateralis of skull.it is the meeting point of four bones, the frontal, parietal, greater wing of sphenoid and the squamous part of temporal bone. The anterolateral fontanelle in the neonatal skulls close after 2-3 months to form the pterion Four types of pterion ( sphenoparietal, frontotemporal, stellate, epipteric) were defined by Murphy in It is commonly employed in surgical treatment of Tumours involving inferior aspects of frontal lobe, like olfactory meningiomas, oribital, retro-oribital sellar, chaismatic, subfrontal, prepontine areas, anterior circulation and basilar artery aneurysm. The knowledge regarding the various shapes and distances from different points to pterion is useful for treating number of pathologies in brain. So this is so useful for neurosurgeons, anatomists, anthropologist and forensic medicine. KEYWORDS: Pterion, fontanelle,meningiomas, basilar artery aneurysm YUVARAJ.M Department of Anatomy, Saveetha Medical College and Hospital, Chennai, Tamilnadu, India. *Corresponding Author Received on: Revised and Accepted on: DOI: B-999

2 INTRODUCTION Pterion is defined as an H- Shaped sutural confluence present in the Norma Lateralis of the skull. It is formed by the junction of four bones namely frontal, parietal, squamous part of temporal and greater wing of sphenoid 1. The pterion corresponds to the anterolateral fontanelle of neonatal skull which closes in the third month after birth 2. Pterion may be considered as an important neurosurgical landmark because, It is related to the frontal or anterior branch of middle meningeal artery, middle cerebral artery, Broca's motor speech area (44,45) to the left, Lateral (Sylvian) cerebral fissure, middle meningeal vein. Pterional approach is useful in performing surgeries with minimal tissue injury without compromising surgical results. It is commonly employed in surgical treatment of Tumours involving inferior aspects of frontal lobe, like olfactory meningiomas, oribital, retro-oribital sellar, chaismatic, subfrontal, prepontine areas, anterior circulation and basilar artery aneurysm. The Pterion is also commonly used in cranial suture closure methodology as an important guide for age estimation and sex determination in archaeological and forensic specimens. The four types of pterion namely the Sphenoparietal, Frontotemporal, Stellate and Epipteric 3. The sphenoparietal type is defined as a sutural pattern in which the sphenoid and parietal bones are in direct contact. Conversely, the frontotemporal type is a stural pattern in which the frontal and temporal bones are in direct contact. The stellate type is characterized by articulation of four bones at a point. A sutural bone is sometimes present at the pterion called as the pterion ossicle or epipteric bone or flower's bone. The present study was made to observe the different shapes of pterion and location of different parameter distances that may be of high importance to neurosurgeons, anthropologists, radiologist, anatomists, and forensic medicine during various surgical and teaching purpose. MATERIALS AND METHODS 125 dry skulls of unknown sex were used for this study; out of which the damaged and diseased skulls were excluded from the study. 250 pterion were studied. Fig: 1The skulls were obtained from the Department of Anatomy, Saveetha medical college and hospital, Chennai. On both the left and right sides of the skull, the sutural pattern of the Pterion was determined based on descriptions (sphenoparietal, frontotemporal, stellate and epipteric types) and the distance from pterion to different parameters was measured and the photographs were taken. RESULTS In this study we have seen the various shapes of pterion and its important from the pterion to various points. The four shapes of pterion was classified and the most predominant was sphenopariteal, frontotemporal, stellate and less common is epipteric. The mean of sphenopariteal , frontotemporal , stellate and epipteric (Table:1). The distance of pterion from various landmarks on both sides in four types of pterion is tabulated in Table 2. Table 1 Four types of Pterion in the present study with percentage. Shapes of pterion Types of pterion Right side% Left side % Average Sphenopariteal Frontotemporal Stellate Epipteric B-1000

3 Table 2 showing the distance of pterion from different points Morphometry of various types of pterion S.NO Sphenoparietal type Frontotemporal type LANDMARK RIGHT CM LEFT CM RIGHT CM LEFT CM Mean SD Mean SD Mean SD Mean SD FZ-P ZA P EM-P HF-P OC-P SR-P Stellate type Epipteric type LANDMARK RIGHT CM LEFT CM RIGHT CM LEFT CM Mean SD Mean SD Mean SD Mean SD FZ-P ZA P EM-P HF-P OC-P SR-P FZ P - FRONTOZYGOMATIC SUTURE TO PTERION ZA P - ZYGOMATIC SUTURE TO PTERION EM P - EXTERNAL ACQUOSTIC MEATUS TO PTERION HF P - HYPHOPHYSEAL FOSSA TO PTERION OC P - OPTIC CANAL TO PTERION SR P - SPHENOIDAL RIDGE TO PTERION Table 3 showing comparison of various shapes of pterion in different population Comparison of various shapes of pterion S.N0 POPULATIONS SPHENOPARIETAL FRONTOTEMPORAL% STELLATE% EPIPTERIC% 1 NIGERIAN[6] INDIAN[6] SOUTH INDIAN[10] NIGERIAN[14] KOREAN[5] NORTH INDIAN[6] TURKISH[9] KENYAN[8] WEST INDIAN[7] PRESENT STUDY (SOUTH INDIAN) Figure 1 Skull taken for the research purpose B-1001

4 DISCUSSION Pterion is a bony landmark placed in the temporal fossa. It is usually H- shape, The main aim of the study was to analyze the types, the reason behind its occurrence and clinical implications of the pterion, location of different parameters from the pterion. A detailed understanding of the pterion is necessary to perform neurosurgery and diagnose and treat pathologies related to this region. The study on the types of pterion was primarily based on the works of Murphy who classifies it into 4 types namely sphenoparietal, frontotemporal, stellate and epipteric. The percentage of occurrence of various shapes of pterion is tabulated in Table 1 and the values obtained in the present study were compared with similar studies performed in other populations; results tabulated in Table 3. The pterion is an important neurosurgical landmark and so we calculated from pterion to other important areas which is helpful approaching pathologies in that area and the different parameters were measured and values were observed and put in the Table:2. The sphenoparietal type Fig :2 is defined as the sutural pattern in which the sphenoid and parietal bones are in direct contact. Sphenoparietal type of pterion is commonly seen in humans compared to the predominance of frontotemporal type of pterion in primates the reason being.in a study by Mary et al, they found 78% of sphenoparietal variety in right side and 70% on the left side. 4 In primate evolution 4, the anterosupeior segment of the squamous part of temporal bone of lower primates became detached from its parent and incorporated into the posterosuperior angle of the greater wing of sphenoid bone of humans, thus changing the pterion pattern from frontotemporal type in non-human primates to the sphenoparietal type of humans. The percentage of prevalence of sphenoparietal type was furnished as 76.5% 5, 87.72% 6 and 91.7% 7 while that obtained in the present study was 75.41%; a comparatively low percentage, than the values obtained in other populations.the frontotemporal type Fig: 3 is considered as a sutural pattern in which the frontal and temporal bones contact each other. The fact that the development of calvarium is tightly coordinated with the growth of the brain, may explain the prevalence of frontotemporal pattern of sutures as reported by Wang, 8. Failure of separation of the anterosuperior segment of the temporal bone results in absence of sphenoparietal and persistance of the frontotemporal pattern. The percentage of frontotemporal type obtained in the present study was 6.52%, a lower value compared to the study done by Oguz, 10% 9 and comparatively higher values than the works of % and 2.4% 7 This haphazard difference between various studies may be due to genetic and environmental factors pertaining to different populations; clearly indicated in the Fig:3 A notable fact B-1002

5 is that, the frontotemporal type is prevalent in nonhuman primates, and the degree of brain development can be assessed in a very minor scale with the shape of pterion. The stellate type Fig: 4 is characterized by the articulation of four bones ( frontal, parietal, temporal, sphenoid ) at a given point. The star shaped appearance of the pterion led to coining of the term - stellate. Articulation of the cranial bones is thought to be under the influence especially MSX2 gene (MSH Homebox 2 - Necessary for proper development throughout the body) The present study accounted to 4.91% of stellate type of pterions, a lower value compared to the percentage obtained by Saxena, Mwachaka, 6,11 which were 7% and 5.71% respectively. The difference may be due to genetic and environmental factors. The epipteric type Fig: 5 is defined by a presence of a small sutural bone between the parietal bone and greater wing of sphenoid. It is a wormian bone and it is also called as a "flower bone" The epipteric bone is an inca bone and it is relatively thin. This causes the radiologists to misunderstand the epipteric oscicle as a fracture in the site, and hence a healthy knowledge about the epipteric ossicle may be mandatory to avoid such confusions both in case of diagnosis and surgery. The present study infers that the epipteric is the second most common variety next to sphenoparietal type according to 13.11% of the skulls. The percentages of occurrence observed by other researchers are Manjunath et al (1993) % 6 Lee et al (2001) % 10 Mwachaka et al (2008) - 12% 11. The pterion plays a important surface land mark for neurosurgeons because thin plate of bone and easy to approach and treat number of pathological conditions like middle meningeal artery may rupture during road traffic accident and produce subdural haematoma and the possible way for correction is putting a burhole in the pterion and reducing the haematoma 12 it has several advantages over traditional craniotomy that including minimal tissue damage, minor brain retraction, a higher cosmotic result and minimal duration of surgery 13 in several studies they have measured the two parameters the distance from pterion to optic canal and pterion to sphenoidal ridge in addition to that we have added the following parameters based on considering the clinical significance during various surgical procedure for treating pathological conditions (table:3). External acoqustic meatus to pterion, Hyphophyseal fossa to pterion Optic canal to pterion. The distance from pterion to hyphophyseal fossa varies in various shapes of pterion in the sphenoparietal it 4.6 [right] and 4.7 [left] in the fronototemporal it 5.4[right] 5.1[left] stellate it 5.2 [right] 4.9 [left] epipteric 4.8 [right] 4.9[left]. The knowledge regarding this distance is very useful for neurosurgeons when they are treating any pathologies relating to pituitary gland. The distance from pterion to optic canal also varies based on the shapes of pterion in sphenoparietal 4.5 [right] 5.0 [Left], fronototemporal 5.3 [Right] 5.2[Left], stellate 4.9 [Right] 5.1 [Left], epipteric 5.6 [Right] 5.2 [Left]. This distance also plays a very important neurosurgeons and ophthalmologist in treating the pathologies treating near the apex of orbit. CONCLUSION The knowledge regarding the various shapes and distances from different points to pterion is useful for treating number of pathologies in brain. So this is so useful for neurosurgeons, anatomists, anthropologist and forensic medicine. This study is primarily aimed done with the skulls of South Indian population, we suggest that the scope of the study can be further carried out in various populations to appreciate the variations better CONFLICT OF INTEREST Conflict of interest declared none. REFERENCES 1. Susan Standring. Gray s Anatomy, The Anatomical Basis of Clinical Practice, 40th edition Churchil Livingstone; 2008 pg: Keith L. Moore T. V. N. Persaud Mark G. Torchia. The Developing Human: Clinically Oriented Embryology 9th Edition, 2011.pg:56 and A. Mary Prabha, C. Venkatramaniah Morphometric study of different types of pterion and its relation with middle meningeal artery in dry skulls of Tamil Nadu, J Pharm Biomed Sci, 2012, 21 (04) Wang, Q. ; Opperman, L.A. ; Havil, L.M.; Carlson, D.S. & Dechow, P.C. Inheritance of sutural pattern at the pterion in Rhesus Monkey skulls. Anat. Rec. Discov. Mol. Cell. Evol. Biol., : Oguz, O.; Sanli, S.G. & Bozkir, M.G.& Soames, R.W. The pterion in Turkish male skulls. Surg. Radiol. Anat., : Manjunath KY, Thomas IM. Pterion variants and epipteric oscicles in South Indian Skulls. Anat Soc India. 1993; 42: Mwachaka, P. M.; Hassanali, J. & Odula, P. Sutural morphology of the pterion and asterion among adult Kenyans. Braz. J. Morphol. Sci., (1): Lama M, Mottolese C. Middle meningeal artery aneurysm associated with meningioma. J Neurosurg Sci. 2000;44(1): Cheng WY, Lee HT, Sun MH, Shen CC. A pterion keyhole approach for the treatment of anterior circulation aneurysms. Minim Invas Neurosur. 2006; 49 (5): Asala SA, Mbajiorgu FE. Epigenetic variation in the Nigerian skull. Sutural pattern at the pterion. East Afr Med J 1996;73:484-6 B-1003

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