Incidence of Metopism in Adult Thai Skulls/ Incidencia de Metopismo en Craneos Tailandeses Adultos.
The metopism is a rare variant suture present on the adult frontal bone because it fails to fuse in early childhood. It is also called the metopic suture or median frontal suture that separates the two halves of the frontal bone in the vertical plane. Although this suture can be found in every newborn skull, the actual disappearance of metopic suture is still recently controversy. Previous investigations have suggested that metopic suture could vary disappear at the end of first year, or in the early second year (Keith, 1948), at the end of the fourth year (Piersol, 1916), by the fifth or sixth year (Romanes, 1972; Torgerson, 1951), by the seventh year (Hamiton, 1976), or by the eight year (Warwick & Williams, 1980). However, in general textbooks of anatomy, metopic suture is defined to usually disappear from infancy to in early childhood.
Clinically, the persistent metopic suture can confuse the radiologists and neurosurgeons during reading the films of X-ray, CT, or MRI in wrong diagnosis in urgent situations. Therefore the knowledge of the metopism incidence in different races is important and should be considered before diagnosis of frontal bone fractures. Previously, the incidence of metopic suture has been reported in many populations such as Scottish (Bryce, 1915), Australian (Bryce), Mongolian (Bryce), European (Bryce), Nigerian (Ajmani et al, 1983), Nepalese (Bilodi et al, 2004) Lebanese (Baaten et al., 2003), Brazilian (Castilho et al., 2006), Indian (Murlimanju et al., 2011), Turkish (Bilgin et al, 2013), and West Anatolian (Aksu et al., 2014). Recently, there is no report of this incidence from Thai population. Therefore we aimed to determine the incidence of metopic suture in Thai adult skulls.
MATERIAL AND METHOD
Seven hundred and six dried skulls (481 males and 225 females), ranging from 29-92 years, were carried out for metopic sutural observations. All skulls were identified and recorded systematically form the Osteological Collection Unit, Department of Anatomy, Faculty of Medicine, Khon Kaen University, Thailand. The analysis of the metopic suture was made by investigation on the skulls at frontal bone. The metopic suture was considered as complete metopic suture when it is present of extra continuous suture extending between the nasion and the bregma (Figs. 1A, 2A and 2B). In addition, the incomplete metopic suture was considered when finding of partial suture extending either from the bregma or from the nasion (Figs. 1B, 1C, 2C and 2D). Note that skulls with visible deformities were excluded from this study. The incidences of all metopic sutures were represented as number of skulls and percentage.
On 706 dried skulls, the results showed that 53 skulls (7.51%) were present of the metopic sutures found 29 (4.11%) skulls in men and 24 (3.40%) skulls in woman (Table I). The metopic sutures observed in this study could be classified into two types (Figs. 1 and 2). The first type was the complete metopic suture (CMS) and the second type was incomplete metopic suture (ICMS), which could be further classified into two subtypes, bregma-incomplete metopic suture (BIMS) and nasion- incomplete metopic suture (NIMS). The CMS type, a suture running between nasion and bregma (Figs. 1A, 2A and 2B), was found in 20 skulls (2.83%); 11 (1.56%) seen in men and 9 (1.28%) in women. For the ICMS, the incidence of BIMS (Figs. 1B and 2D) and NIMS (Figs. 1C and 2C) were 33 skulls (4.67%) found 18 skulls in men (2.55%) and skulls 15 in women (2.12%) as shown in Table I.
This is the first report about the incidence of metopic suture determined in 706 dried skulls of identified Thai adults. In the same veins of a previous study (Skrzat et al., 2004), this present study also classified the metopic suture into two major patterns or shapes (complete and incomplete) (Table I). In addition, the incomplete metopic suture can be subdivided into two types: bregma-incomplete metopic suture (BIMS) and nasion-incomplete metopic suture (NIMS) as shown in Figures 1 and 2. Moreover, there was a report showing five shapes (complete, incomplete, linear, V, and double) of metopic suture in Indian population (Murlimanju et al.). As compared to total incidence of metopic suture among racial variations, the incidence in the present Thai study (7.51%) is very close to that of Brazilian population (7.4%) (Castilho et al.), and higher than that of Australian (1%) (Bryce), Mongolian (5.1%) (Bryce), Nigerian (3.4%) (Ajmani et al.), Nepalese (3.93%) (Bilodi et al.), Lebanese (0.82%) (Baaten et al.), Indian (1.2%) (Murlimanju et al.). With respect to sex, the metopic suture in both types is found to be higher in males than in females (Table I) witch corresponds to that of Indian and Lebanese populations (Murlimanju et al.; Baaten et al.). Similar to the other populations, the incidence of incomplete metopic suture of Thais was higher than that of the complete metopic suture (Table I). Interestingly, the fusion or disappearance of the metopic suture in Thai population is still unknown and needs further investigations. The information or awareness about the incidence of persistent metopic suture is very important for clinicians in emergency diagnosis of some adult head injury cases to prevent misinterpreted as vertical frontal fracture in x-rays, CT, or MRI film. In conclusion, the present study has provided the first incidence of metopic suture in the Thai adult population.
We would like to thank the Osteological Collection Unit, Department of Anatomy, Faculty of Medicine, Khon Kaen University, Thailand for providing the identified human skulls.
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Department of Anatomy
Faculty of Medicine
University Muang Khon Kaen
Khon Kaen, 40002
Kimaporn Khamanarong *; Panya Tuamsuk *; Worawut Woraputtaporn *; Malivalaya Namking *; Tarinee Sawatpanich *; Yanyong Toomsan * & Sitthichai Iamsaard *
* Department of Anatomy, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
Caption: Fig. 1 Schematic drawing of three different metopic sutures on skulls observed in this study. A. Complete metopic suture (CMS), B. Bregma-incomplete metopic suture (BIMS), and C. Nasionin-complete metopic suture (NIMS).
Caption: Fig. 2 Showing representative dried skulls with variant metopic sutures. A. anterior view and B. superior view, complete metopic suture (CMS), C. anterior view, nasion- incomplete metopic suture (NIMS), D. superior view, bregma-incomplete metopic suture (BIMS). Br = bregma, N= nasion, Ant.= anterior, Post.= posterior.
Table I. Incidence of the metopic sutures observed on 706 dried skulls of indentified adult Thais. Metopic sutural types Males Females Total Complete metopic suture 11 (1.56%) 9 (1.28%) 20 (2.83%) Incomplete metopic suture 18 (2.55%) 15 (2.12%) 33 (4.67%) Total 29 (4.11%) 24 (3.40%) 53 (7.51%)