Classification and Incidence of Pterion Patterns of Thai Skulls/ Clasificacion e Incidencia de los Patrones de Pterion en Craneos de Tailandia.
In general, the pterion in lateral aspect of the human skull is usually an irregular H shaped suture. It is formed by articulation of the frontal, parietal, greater wing of sphenoid and the squamous part of temporal bones. It is the weakest part of the skull owing to the relatively thin bone and is commonly used as a landmark for neurosurgery related to many structures within cranial cavity such as middle meningeal artery and Broca's area (Escosa-Bage et al., 2002; Lindsay et al., 1991). Clinically, the variant patterns of pterion can also confuse the clinicians during diagnosis of the lateral skull fractures in emergency condition. Interestingly, the types and positions of the ptrion have been well reported to be varying in different races (Morales et al., 2011). Previously, the patterns of pterion have been documented in various populations including Australian Aborigines (Murphy, 1956), Indians (Ahuja et al., 1971; Saxena et al, 2003; Natekar et al, 2010), North Indians (Agarwal et al., 1980; Seema & Mahajan, 2014), Japanese (Matsumura et al, 1991), Turks (Ersoy et al, 2003), Turkish (Oguz et al, 2004), Kenyas (Mwachaka et al, 2009), Gujurat (Zalawadia et al., 2010), Koreans (Lee et al., 2001), and Nigerians (Eboh and Obaroefe, 2014; Asala and Mbajiorgu, 1996). Although an incidence about skull morphology like the metopism, a rare variant suture persistence, in Northeastern Thais has been previously documented (Khamanarong et al., 2015), there is no later report about classification of pterion formation in our population. Therefore, this study aims to investigate the incidence and to classify the variations of the configuration of sutural pattern of pterion in Thai skulls.
MATERIAL AND METHOD
A total of 110 sides of infratemporal fossa samples from 55 dried skulls identified as Northeastern Thais were used. Fifty four samples were adult dried skulls (37 males and 17 females, ranging from 27 to 89 years of age at decease). One female teen-ager's skull, (13 years of age at death) was also used. All skulls were identified and recorded systematically form bone Collection Unit, Department of Anatomy, Faculty of Medicine, Khon Kaen University, Thailand. Both sides of the infratemporal fossa were systemically investigated to classify the pattern of articulation of the pteria and recorded. The data were then analyzed using descriptive statistics.
We found that the pterion patterns of Thai skulls could be classified into 4 different types as shown in Figures 1. The incidence of each pterion pattern was shown in Table I. Type 1 is the spheno-parietal type, irregular H like-shaped suture, formed by articulation of the frontal, parietal, greater wing of the sphenoid and the squamous part of temporal bones. Apparently, the sphenoid bone of this type directly contacted to the parietal bone (Fig. 1A). It was the most frequent type, found in 96 (left 48, right 48; 87.27 %) out of 110 sides of the skulls. Type 2 is the fronto-temporal type with irregular K like-shaped suture, in which the frontal bone directly contacts to the temporal bone (Fig. 1B). This type was rare and found as in 4.55 % of total skull sides. Type 3 is the uni-epipteric type, in which a small irregular-shaped epipteric (also called pterion ossicle, sutural or Wormian) bone was found interposing within this type of pterion (Fig. 1C). It was found in only 7 sides (6.36 %) of specimens (5 males and 2 females). Type 4, the specimen with multiple small irregular-shaped epipteric bones interposed within a pterion, was classified as multi-epipteric type (Fig. 1D) which as observed only in 2 sides (1.82 %) of the female's skull.
In addition, symmetry in the types of pterion was detected in 47 (31 males and 16 females) specimens (Table II). The bilateral spheno-parietal and fronto-temporal types occurred in 44 (93.61 %) and 2 (4.26 %) skulls, respectively. No symmetry was observed in uni-epipteric type of pteroin. The bilateral multi-epipteric type was rare, observed only in a female specimen (2.13 %).
The pterion is used as an important anatomical landmark for many regions of the brain with respect to neurosurgery. The morphological variability of pterion has been documented in various populations (Murphy; Ahuja et al.; Agarwal et al.; Matsumura et al.; Lee et al. 2001; Saxena et al.; Ersoy et al.; Oguz et al.; Mwachaka et al.; Zalawadia et al.; Natekar et al.; Seema & Mahajan; Eboh & Obaroefe). Basically, the patterns of pterion have been classified into 4 types: spheno-parietal, fronto-temporal, stellate, and epipteric types (Seema & Mahajan). In the present study, spheno-parietal, fronto-temporal, uniepipteric and multi-epipteric types were detected. The stellate type, in which the frontal, parietal, sphenoid and the temporal bones interconnected to each other (Murphy and Saxena et al.) was not observed. The spheno-parietal type was the most common type observed in Thais (87.27%). When the present data were compared with other races, the frequency of the spheno-parietal type in Thais was similar to the most common finding in the following races: Turks, 87.35 % to 88 % (Oguz et al.; Ersoy et al.); Indians, 84.72 to 85.33 % (Saxena et al.; Natekar et al.), and in North Indians 89 %, (Seema & Mahajan). The low frequency of the incidence of the fronto-temporal type (4.55 %) in Thais was similar to that reported in North Indians (4.35%) by Agarwal et al. While the incidence of 8.18% for both epipterics (uni-epipteric 6.36% and multi-epipteric 1.82%) in Thais is very close to that of Turks (8.98 %) reported by Ersoy et al.
In the case report by Satheesha & Soumya (2008), they found only three epipteric bones on the right pterion region in Indian adult skulls. In the preset study, we detected a unique type, in which 4 unusual small irregular-shaped of epipteric bones inserted within the pteria of both sides (Type 4, muti-epipteric). This was rare in incidence, occurring only 1.82 % of a total of 110 specimens. The variation of pterion which contained unusual epipteric bones may lead to surgical pitfall in cranial surgery. The bilateral symmetrical type of pterions was found in 47 of 55 skulls. The most frequent type was the bilateral spheno-parietal type (93.61 %).
In conclusion, the knowledge of the pterion types in relation to many brain landmarks may be important for neurosurgical interventions and for clinicians during diagnosis of the lateral skull fractures in emergency situations. The detailed anatomical information of variation pterion in Northeastern Thais will help the surgeons for operation planning.
ACKNOWLEDGMENTS. We would like to thank Department of Anatomy, Faculty of Medicine, Khon Kaen University for providing the identified human skulls.
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Dr. Sitthichai Iamsaard
Department of Anatomy
Faculty of Medicine
Khon Kaen University
123 Mitrapap Road
Khon Kaen 40002
Wunnee Chaijaroonkhanarak (1); Worawut Woraputtaporn (1); Parichat Prachaney (1);Pattama Amarttayakong (1); Kimaporn Khamanarong (1); Wanassanun Pannangrong (1); Jariya Umka Welbat (1,2) & Sitthichai Iamsaard (1,3 [dagger])
(1) Department of Anatomy, Faculty of Medicine, Khon Kaen University, 123 Mittaparb Road, Maung, District, Khon Kaen, 40002, Thailand.
(2) Center for Research and Development of Herbal Health Product, Faculty of Pharmaceutical Sciences, Mittaparb Road, Khon Kaen, 40002, Thailand.
(3) Reproductive Biomedicine Research Group, Khon Kaen University, Khon Kaen, Thailand.
Caption: Fig. 1. Photographs (left panel) with schematic suture patterns (right panel) showing lateral view of dried skulls observed in Thais. They were classified into 4 different pterion patterns: A) Spheno-parietal type, B) Fronto-temporal type, C) Uni- type, and D) Multi-epipteric type. P; parietal bone, F; frontal bone, T; temporal bone, S; sphenoid bone, e; epipteric bone (as known as pterion ossicle, sutural or Wormian bone).
Table I. Incidence of pterion types observed on left and right sides of Thai skulls. Males Types of (individual side of both sexes, n = 55) pterion Left side % Right side % Spheno-parietal type 34 61.81 34 61.81 Fronto-temporal type 0 0 1 1.81 Uni-epipteric type 3 5.45 2 3.63 Multi-epipteric type 0 0 0 0 Females Types of (individual side of both sexes, n = 55) pterion Left side % Right side % Spheno-parietal type 14 25.45 14 25.45 Fronto-temporal type 2 3.63 2 3.63 Uni-epipteric type 1 1.81 1 1.81 Multi-epipteric type 1 1.81 1 1.81 Types of Total pterion (N = 110) Spheno-parietal type 96 87.27 Fronto-temporal type 5 4.55 Uni-epipteric type 7 6.36 Multi-epipteric type 2 1.82 Table II. Incidence of bilateral symmetry in individual type of pterion patterns on Thai skulls. Types of pterion with Males Females Total % bilateral symmetry N % N % N % Spheno-parietal type 31 65.96 13 27.65 44 93.61 Fronto-temporal type 0 0 2 4.26 2 4.26 Uni-epipteric type 0 0 0 0 0 0 Multi-epipteric type 0 0 1 2.13 1 2.13 Total 31 65.96 16 43.04 47 100