Introduction:
Wormian bones [sutural bones or supernumerary bones], are considered to be the accessory bones, that are developed within the sutures of the skull bones. They are frequently observed in the lambdoid suture.(1) However, a few of these bones are also seen in pterion, where these are known as pterion ossicle or epipteric bone.(2-5) A few are also seen at the lambda, where they are known as Inca bones since they are frequently sighted at this site in the mummified Peruvian skulls.(6,7)
Although their formation is controversial, a few authors claim that they are developed from external influences, genetically determined, detached portion of the primary ossification centres of the adjacent membrane bones.(8-10) Wormian bones are commonly seen in healthy individuals. However, their number increases in certain conditions like cleidocranial dysostosis, rickets, osteogenesis imperfect.(11) It is also claimed that the presence and number of these bones differ in different races and hence can be used in forensic medicine.(12) Due to all these significances, the present study is aimed to note the topographical presence and the number of these bones in dried human cadaveric skulls.
Materials and Method
Eighty-eight dry human adult skulls of unknown age and sex, were used for this study. Disarticulated skulls were excluded. All the cranial sutures were observed for the presence of the wormian bones.
Results
Out of the eighty-eight skulls, wormian bones were seen in 45 skulls and in the rest of the skulls they were absent. The results are tabulated in Table 1. It can be noted that no wormian bones were observed at the coronal suture and the sagittal suture.
| Table 1: Results of the Study |
Location of wormian bones |
Number of skulls |
Lambdoid suture |
43 |
Lambda |
8 |
Pterion |
3 |
Asterion |
8 |
Total |
62 |
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Figure 1: Chart showing the presence of wormian bones |
A total of nine wormian bones were observed at the lambdoid suture in one skull (Fig. 2). In thirty skulls (54%), the wormian bones were present at the lambdoid suture (Fig. 2). One among these thirty skulls, showed as many as nine wormian bones along the length of the lambdoid suture (Fig. 3). In twenty-three skulls (42%), the wormian bones were present at the asterion (Fig. 4) and in two skulls (4%), the wormian bones were seen at the pterion (Fig. 5).
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Fig 2: Wormian bones (*) at the lambdoid suture |
Fig 3: Nine wormian bones (*) at the lambdoid suture |
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Fig 4: Wormian bone (*) at the asterion |
Fig 5: Wormian bone (*) at the pterion |
Discussion
Wormian bones are a common finding. Their location, size and number vary largely. According to Bergman et al., lambdoid suture is the most common site of sutural bones in about 40% of the skulls. This was followed by asterion [former posterolateral fontanelle] and the lambda.(13) But according to Chambellan, the second commonest site of wormian bones is the coronal suture.(14) However, according to Nayak, the second commonest site is the pterion [epipteric bone].(5,15,16)
Parker, way back in 1905 suggested that the number of wormian bones is directly proportional to the length of the suture.(17) It is postulated that the formation of wormian bones is unknown. However, mechanical or genetic factors are responsible for the sutures to move apart and hence, the wormian bones would arise in the sutures and the fontanelles, rather than within any other individual bone.(1) The incidence of occurrence of wormian bones may be used to detect any anomalies associated with the central nervous system. It is also shown that small-sized, fewer wormian bones would be found in a normal individual, however, an individual with more than ten wormian bones needs to be thoroughly investigated for any underlying pathology.(10,18,19) In the present study, one skull with nine wormian bones were seen in the lambdoid suture.
Embryological Significance: It may be noted that these wormian bones are located at the vicinity of the parietal bones. The ossification of the parietal bone begins from the center and radiate towards the periphery in the form of needle-like bone spicules.(20) This would further close the suture and subsequently, the fontanelles. Hence, the formation of these wormian bones would be attributed to insufficient rate of closure of the suture. These bones further articulate with the surrounding bones by sutures and thus would be of variable shapes and sizes. (21) Wormian bones may also develop as a result of abnormal ossification centers in the cranium.
Clinical Importance: The wormian bones may pose serious complications for radiologist in differentiating them from a skull fracture, that may be as a result of trauma, accident or physical abuse. This would further cause delay in administering the appropriate treatment. Owing to the less thickness of bones, the pterion acts as a keyhole for numerous intracranial surgeries, thereby permitting access to frontal and temporal lobes.(22-24) Hence, the presence of wormian bones at this site may cause complications in making burr holes.(25) Therefore, the findings of the present study have added additional information to the existing findings.
References
- Sanchez-lara, PA, Graham JM, Hing AV, Lee J, Cunningham M. The morphogenesis of Wormian bones: a study of craniosynostosis and purposeful cranial deformation. A J Med Genet A. 2007; 143(24):3243-51.
- Malhotra VK, Tewari PS, Pandey SN, Tewari SP. Interparietal bone. Acta Anat. (Basel). 1978;101:94-6.
- Das S, Suri R, Kapur V. Anatomical observations on os inca and associated cranial deformities. Folia Morphol. 2005;64:118-21.
- Jaffar AA. Sutural bones. 2009; 10:25. Available at http://archive.li/4kkSM
- Nayak S. Presence of Wormian bone at bregma and paired frontal bone in an Indian skull. Neuroanatomy. 2006;(5):42-3.
- Parente K, Mercado-Deane MG, Brummund T. Radiological case of the month. Arch Pediatr Adolesc Med. 2001;155(6):731-2.
- Saxena SK, Chowdhary DS, Jain SP. Interparietal bones in Nigerian skulls. J Anat. 1986;144:235-37.
- Murphy T. The pterion in Australian aborigine. Am J Phys Anthropol. 1956;14(2):225-44.
- Pal GP. Variations of the interparietal bone in man. J Anat. 1987;152:205-8.
- Cremin B, Goodman H, Spranger J, Beighton P. Wormian bones in osteogenesis imperfecta and other disorders. Skeletal Radiol. 1982;8(1):35-8.
- Burgener FA, Kormano M. Bone and joint disorders, conventional radiologic differential diagnosis. New York: Thieme medical publishers, 1997. p. 130.
- Hernandez FG, ECcheverria GM. Frequency of bone skulls with lambdoid in artificial deformation in Northern Chile. Int J Morphol. 2009;27(3):933-8.
- Bergman RA, Afifi AK, Miyauchi R. Skeletal systems: Cranium. In: Compendium of human anatomical variations. Baltimore, Urban and Schwarzenberg. 1988;197–205.
- Chambellan V. Etude anatomique et anthropologique sur les os wormiens. Paris: Inaugural Thése, 1883. p. 66.
- Murlimanju BV, Prabhu LV, Ashraf CM, Kuma CG, Rai R, Maheshwari CJ. Morphological and topographical study of Wormian bones in cadaver dry skulls. Morphol. Sci. 2011;28(3):176-9.
- Saxena SK, Jain SP, Chowdhary DS. A comparative study of pterion formation and its variations in the skulls of Nigerians and Indians. Anthropologischer Anzeiger. 1988;46(1):75-82.
- Parker CA. Wormian bones. Chicago: Robert Press, 1905.
- Jeanty P, Silva SR, Turner C. Prenatal diagnosis of Wormian bones. J Ultrasound Med. 2000;19(12):863-9.
- Kaplan SB, Kemp SS, Oh KS. Radiographic manifestations of congenital anomalies of the skull. Radiol Clin North Am. 1991;29(2):195-218.
- Sadler TW. In Langman’s medical embryology. Chapter The axial skeleton. 12th ed. Lippincott Williams and Wilkins. Pp. 135.
- Barberini F, Bruner E, Cartolari R, Franchitto G, Heyn R, Ricci F, Manzi G. An unusually-wide human bregmatic Wormian bone: anatomy, tomographic description and possible significance. Surg Radiol Anat. 2008;30(8):683-7.
- Scholz M, Parvin R, Thissen J, Lohnert C, Harders A, Blaeser K. Skull base approaches in neurosurgery. Head Neck Oncol. 2010;2:16.
- Chao S, Shen C, Cheng W. Microsurgical removal of sylvian fissure lipoma with pterion keyhole approach-case report and review of the literature. Surg Neurol. 2008;70 Suppl 1:S85-S90.
- Cheng W, Lee H, Sun M, Shen C. A pterion keyhole approach for the treatment of anterior circulation aneurysms. Minim Invasive Neurosurg. 2006;49(5):257-62.
- Samson D, Hodosh R, Clark W. Microsurgical evaluation of the pterional approach to aneurysma of the distal basilar circulation. Neurosurgery. 1978;3(2):135-41.
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