|Year : 2014 | Volume
| Issue : 4 | Page : 189-190
Inca bones at asterion
Prashant E Natekar1, Suhit E Natekar2, Fatima M De Souza1
1 Department of Anatomy, Bambolim, Goa, India
2 Goa Medical College, Bambolim, Goa, India
|Date of Web Publication||13-Dec-2014|
Prashant E Natekar
Department of Anatomy, Goa Medical College, Bambolim 403 202, Goa
Source of Support: None, Conflict of Interest: None
Background: Surgical approach towards asterion has to be done with caution as many surgeons are unfamiliar with the anatomical variations. The asterion corresponds to the site of the posterolateral (mastoid) fontanelle of the neonatal skull which closes at the end of the first year. Inca bones provide information as markers for various diseases, and can mislead in the diagnosis of fractures. Observation and Results: 150 dry skull bones from the Department of Anatomy at Goa Medical College, India and other neighboring medical colleges by examining the asterion, and its sutural articulations with parietal, temporal and occipital bones and also anatomical variations if any in adults. Discussion: The anatomical landmarks selected must be reliable and above all easy to identify. Bony structures are more suitable than soft tissue or cartilaginous landmarks because of their rigid and reliable location. Presence of these bones provides false impressions of fractures or the fractures may be interpreted for inca bones especially in the region of asterion either radiologically or clinically which may lead to complications during burr hole surgeries.
Keywords: Asterion, Inca bone, Posterolateral fontanelle, Wormian bones
|How to cite this article:|
Natekar PE, Natekar SE, De Souza FM. Inca bones at asterion. Indian J Otol 2014;20:189-90
| Introduction|| |
The asterion is the junction of the parietal, temporal, and occipital bones.  The asterion corresponds to the site of the posterolateral (mastoid) fontanelle of the neonatal skull, which closes at the end of the 1 st year.  The joints of the cranial vault are sutural joints, which ossify in membranes. As the bones are growing the unossified sutural membranes intervene between their apposed margins. These sutural membranes connect the periosteum covering the outer and inner surfaces of the bone which helps in growth as well as binding the bones together at their apposed margins.
Inca bones provide information as markers for various diseases, brittle bone disease osteogenesis imperfecta,  neurocranial variables , and can mislead in the diagnosis of fractures.  This study is carried out so as to keep ourselves abreast in the diagnosis of fractures at the site of asterion its anatomical variations and also trephing of the skull during operation.
| Materials and Methods|| |
This study is carried out on 150 dry skull bones from the Department of Anatomy at Goa Medical College, India and other neighboring medical colleges by examining the asterion, and its sutural articulations with parietal, temporal, and occipital bones and also anatomical variations if any in adults.
| Observation and Results|| |
In this study, it was observed that 12.6% of the asterion showed presence of single inca bone as shown in [Table 1] and [Figure 1].
|Table 1: Percentage distribution of inca bone at asterion in different population|
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In our study, it was seen that inca bones at the asterion was 12.6%, whereas in North Americans 12%, South Americans 7.5%, Egyptians 14.4%, Indians-Burma 14.7%, Indians-Punjab 16.9%,  Australian aborigines 19.82%,  Turks 9.92%,  and Kenyans was 20%. 
| Discussion|| |
Asterion is an important anatomical landmark which is situated at the junction of parietal, temporal, and occipital bones. One or more inca bones may appear at the mastoid fontanelle. They vary greatly in size but more or less symmetrical. Sutural bones appear in great numbers in hydrocephalic skulls and they have been linked with rapid cranial expansion. Our earlier studies reveal presence of epipteric bones at pterion.  Studies also reveal that the wormian bones are located in the lambdoid suture and fontanelle (masto-occipital suture). The second most common occurrence (about 25%) is in the coronal suture. The rest occur in any remaining sutures and fontanelles.  The presence of these inca bones at asterion may also complicate surgical orientation leading to pitfalls.
Although inca bones can be found as normal variants, various etiologies have been proposed are racial feature of Native American Indian populations. This etiology illustrates the longevity of some erroneous medical theory, even when they have long been disproved.  Consequence of skull deformation. Incidence of wormian bones in deformed and undeformed skulls of Southwestern Indians, concluded that there is no significant difference between these two groups.  An adaptation to cranial enlargement. There is a relationship with the total length of sutures. Greater the sutural length of skull greater the number of wormian bones. Metabolic disorders. Formation of wormian bones could result from metabolic disorders of the mesoderm.  An autosomal dominant trait. Wormian bones are inherited as a dominant trait with incomplete penetrance and variable expression. 
Presence of these bones provides false impressions of fractures or the fractures may be interpreted for inca bones, especially in the region of asterion either radiologically or clinically, which may lead to complications during burr hole surgeries. Although their occurrence is less frequent, their presence may serve as a marker for the identification of various anomalies of the central nervous system dysmorphic features and syndromes. It is therefore relevant to surgeons and radiologists to have this essential information before and during surgical intervention.
In our study, 12.6% of the inca bones were seen at the asterion when compared with that of the various populations as shown in [Table 1]. This study will also contribute additional information of skull bone fractures in infancy and early childhood, which may be associated with large intersutural bones giving false appearance of fracture radiologically, and also during surgical interventions involving burr-hole surgeries as their extensions may lead to continuation of fracture lines.
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