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Table of Contents
ORIGINAL ARTICLE
Year : 2020  |  Volume : 69  |  Issue : 2  |  Page : 97-102

A study on differences in the obliteration of cranial sutures and their clinical significance


1 Department of Anatomy, Career Institute of Medical Sciences, Ghaila, Uttar Pradesh, India
2 Department of Anatomy, Maharishi Markandeshwar Institute of Medical Sciences and Research, Maharishi Markandeshwar University, Mullana, Ambala, Haryana, India
3 Department of Anatomy, Kanachur Institute of Medical Sciences, Natekkal, Karnataka, India
4 Department of Anatomy, Prasad Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
5 Department of Community Medicine, Yenepoya Medical College, Yenepoya University, Managalore, Karnataka, India

Date of Submission16-Dec-2020
Date of Acceptance22-May-2020
Date of Web Publication30-Jun-2020

Correspondence Address:
Prof. Venkatesh G Kamath
Department of Anatomy, Maharishi Markandeshwar Institute of Medical Sciences and Research, Maharishi Markandeshwar University, Mullana, Ambala - 133 203, Haryana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JASI.JASI_240_19

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  Abstract 


Introduction: There are very few studies on the patency of cranial sutures, and this study analyzes the difference in sutural patency. The objective was to study the difference in the patency of coronal, sagittal, and lambdoid sutures in Indian human adult skulls. Material and Methods: This study involved 120 Indian human adult skulls. The suture patency was graded in accordance to a classification proposed by Sabini and Elkowitz on a scale of 0–4. An open suture was classified as 0; fused but not obliterated as 1; and Grades 2, 3, and 4 represented <50%, >50%, and 100% of obliteration, respectively. Results: The lambdoid sutures were observed to be the most patent and least obliterated. Grade 1 sutures were observed to be 44.71% in lambdoid, 8.4% in sagittal, and 7.3% in coronal sutures. Grade 2 sutures were observed to be 42.6% in lambdoid, 49.3% in sagittal, and 46.7% in coronal sutures. Grade 3 sutures were observed to be 10.1% in lambdoid, 32.1% in sagittal, and 36.2% in coronal sutures. Grade 4 sutures were observed to be 2.6% in lambdoid, 10.2% in sagittal, and 9.8% in coronal sutures. No open sutures were observed. Discussion and Conclusion: Lambdoid sutures are more patent than coronal and sagittal sutures. This can be attributed to the presence of more muscular contractile forces acting on the lambdoid suture when compared with other sutures. The mechanisms involved in suture closure are complex and involve genetic and environmental factors, age, and tissue interactions. Therefore, more advanced research is essential for a clearer insight on this subject, which has immense clinical implications in neuroscience.

Keywords: Cranium, lambdoid, morphology, obliteration, suture


How to cite this article:
Alam MT, Kamath VG, Hema N, Srivastav A K, Patil S. A study on differences in the obliteration of cranial sutures and their clinical significance. J Anat Soc India 2020;69:97-102

How to cite this URL:
Alam MT, Kamath VG, Hema N, Srivastav A K, Patil S. A study on differences in the obliteration of cranial sutures and their clinical significance. J Anat Soc India [serial online] 2020 [cited 2020 Sep 21];69:97-102. Available from: http://www.jasi.org.in/text.asp?2020/69/2/97/288673




  Introduction Top


The term suture is coined from the Latin word “sutura,” symbolizing serrated fibrous interdigitations.[1] Such interdigitations are found in the craniofacial skeleton, and their complexity increases with age.[2] Facial sutures are more patent than cranial due to greater tensile forces and more movement in the face.[2],[3] Suture obliteration has diverse clinical implications as early obliteration results in craniosynostosis.[4] Obliteration is a multifactorial phenomenon depending on age, genetic factors, tensile stresses, brain growth, tissue interactions, and biochemical signaling.[5],[6],[7] Therefore, age estimation using only suture obliteration is unreliable.[8] However, suture obliteration can be used with other cranial indicators to conclusively determine the age.[9],[10] The role of transforming growth factor-beta (TGF-β) in cranial suture obliteration is now conclusively established in physiological mouse models.[11] Lambdoid suture is reported to show prolonged patency and least obliteration compared to other sutures.[3],[12] Because suture obliteration is a complex multifactorial phenomenon, more research is needed in this field to have a clearer insight. The age of the skull was not known in this study and therefore is a limitation. In this study, only the ectocranial aspect of the suture was studied. The authors believe that in future, the endocranial aspect of sutures and their microscopic and radiological evaluation can be performed in skulls in different age groups for better understanding on the subject.


  Material and Methods Top


The study involving 120 skulls was conducted in the department of anatomy in three medical institutes in India. This includes Maharishi Markandeshwar Institute of Medical Sciences and Research, Mullana, Ambala; Career Institute of Medical Sciences, Lucknow; and Kanachur Institute of Medical Sciences, Mangalore. The degree of obliteration of cranial sutures was studied in 120 Indian human adult skulls. Skulls with deformities and damaged sutures were excluded from the study. The age and sex of crania were not known in this study. Only the ectocranial surface of sutures was studied. The endocranial surface of the sutures was not studied, and microscopic evaluation was not performed. The coronal, sagittal, and lambdoid sutures were graded in accordance to the grading pattern proposed by Sabini and Elkowitz.[3] An open suture was classified as 0; fused but not obliterated as 1; and Grades 2, 3, and 4 represented < 50%, >50%, and 100% obliteration, respectively. The criteria used for grading obliteration are shown in [Table 1].
Table 1: The grading pattern used in the study. The pattern is in accordance to the grading pattern proposed by Sabini and Elkowitz[3]

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The degree of obliteration of sagittal suture is noted and graded accordingly as shown in [Figure 1], [Figure 2], [Figure 3], [Figure 4]. A Grade 1 sagittal suture which is fused but not obliterated is shown in [Figure 1]. A Grade 2 suture which is < 50% obliterated is shown in [Figure 2]. A Grade 3 suture which is >50% obliterated is shown in [Figure 3]. A Grade 4 suture which is 100% obliterated is shown in [Figure 4]. Similarly, coronal and lambdoid sutures were also graded, and the frequency of different grades was recorded. The data obtained were analyzed statistically using the Statistical Package for the Social Sciences (SPSS) software (SPSS, IBM Co., Armonk, NY, USA, version 20.0) with Chi-square test. P < 0.001 was considered statistically significant.
Figure 1: A Grade 1 suture which is fused but not obliterated

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Figure 2: A Grade 2 suture which is <50% obliterated

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Figure 3: A Grade 3 suture which is >50% obliterated

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Figure 4: A Grade 4 suture which is 100% obliterated

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  Results Top


No Grade 0, open sutures were observed. The lambdoid sutures were observed to be the least obliterated and most patent. Grade 1 sutures were 44.71% in lambdoid, 8.4% in sagittal, and 7.3% in coronal sutures. Grade 2 sutures were 42.6% in lambdoid, 49.3% in sagittal, and 46.7% in coronal sutures. Grade 3 sutures were 10.1% in lambdoid, 32.1% in sagittal, and 36.2% in coronal sutures. Grade 4 sutures were 2.6% in lambdoid, 10.2% in sagittal, and 9.8% in coronal sutures. The frequency of different grades is summarized in [Table 2].
Table 2: The observed frequency of different grades of cranial sutures

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In lambdoid sutures, Grade 1 had the highest frequency, followed by Grades 2, 3, and 4. In sagittal and coronal sutures, the highest frequency was exhibited by Grade 2, followed by Grades 3, 4, and 1. It was observed that the coronal and sagittal sutures tend to be more obliterated and less patent. Therefore, the highest frequency of Grade 3 and 4 sutures was observed in coronal and sagittal sutures, respectively. In contrast, the highest frequency of Grade 1 and 2 sutures was observed in the lambdoid suture, suggesting that these sutures tend to be more patent and least obliterated.

The frequency of different suture grades observed is summarized in [Figure 5], [Figure 6], [Figure 7]. The observed data were analyzed using the Chi-square test, and the results of the test are summarized in [Table 3]. Statistical analysis showed that all observations were statistically significant with P < 0.001. This conclusively establishes that lambdoid sutures are more patent than the coronal and sagittal sutures.
Figure 5: The frequency of different suture grades observed in the coronal suture

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Figure 6: The frequency of different suture grades observed in the sagittal suture

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Figure 7: The frequency of different suture grades observed in the lambdoid suture

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Table 3: The test statistics

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  Discussion Top


Sutures are fibrous joints in the craniofacial skeleton and are simple at birth.[1] They develop complex interdigitations due to constant growth and resorption of the surrounding bones.[13] Over the years, sutures become completely obliterated with a calcified tissue.[2] Patency of sutures during the early period of development allows brain growth without raising intracranial tension, and, hence, early obliteration of sutures leading to craniosynostosis can be fatal.[14]

The morphology of the sutures depends on multiple factors, both extrinsic such as the muscle tension and intrinsic such as brain growth and genetics.[15],[16],[17] In an experiment on rats, when their temporalis muscle was removed, the regional skull growth reduced and the sutures became more simple.[16] This proves that suture complexity is directly proportional to the tensile forces acting on the suture. These interdigitations increase the surface area of contact of the cranial bones and transfer the tensile forces acting on the suture.[18] It is believed that reduced bone growth and bone movement is associated with early obliteration of the regional sutures.[19] Moreover, sutures transplanted from one location to another in rats were successfully taken up at the new site.[20] Therefore, suture patency and obliteration is a phenomenon with several lacunae available for researchers to explore.

Sabini and Elkowitz examined 17 female and 19 male skulls in the age range of 56–101 years. They concluded that there is no association between grade of the suture and sex and age of the individual. It was also observed that the lambdoid sutures show prolonged patency compared to other sutures.[3] Murlimanju et al. examined 78 human dry skulls of unknown age and sex in the Indian ethnic group. They observed a high frequency of Grade 2, followed by Grades 1, 3, and 4 among lambdoid sutures. Statistical analysis conclusively established that the lambdoid suture has prolonged patency compared to other cranial sutures.[12] Bolk examined 1820 skulls and reported delayed obliteration of lambdoid sutures. In their study, the suture obliteration was 0.27% in lambdoid, 0.65% in coronal, and 3.9% in sagittal sutures.[21] Parsons and Box also stated that the lambdoid sutures were the last among the cranial sutures to obliterate completely.[22] All the above-mentioned studies imply that lambdoid sutures remain more patent and less obliterated. Different studies have used different methods, statistics, and grading patterns. In our study, we observed that in lambdoid sutures, Grade 1 exhibited the highest frequency, followed by Grades 2, 3, and 4. The highest frequency of Grade 1 and 2 sutures was observed in the lambdoid suture, suggesting that these sutures tend to be more patent and least obliterated. In contrast, the highest frequency of Grade 3 and 4 sutures was observed in coronal and sagittal sutures, suggesting that these sutures tend to be more obliterated and less patent.

Suture patency and obliteration depends significantly on the tensile forces acting on the suture.[1],[2] The pull of muscles and ligaments attached around the suture delays obliteration.[3] The lambdoid suture experiences maximum stress from muscular pull when compared to other sutures. This is because a large number of muscles are attached to the occipital bone such as rectus capitis posterior major, rectus capitis posterior minor, semispinalis capitis, rectus capitis anterior, rectus capitis lateralis, longissimus capitis, obliquus capitis superior, occipitalis, splenius capitis, and sternocleidomastoid. The ligamentum nuchae also plays a significant role as it is attached to the spines of the cervical vertebrae and the external occipital protuberance.[23] A concept called “myofascial continuity” states that muscles that cross joints while moving from their origin to insertion exert significant action at the sites of insertion. This is very much true with muscles in the back of the neck that cross the cervical vertebrae and are attached to the occipital bone. These muscles and ligaments that move the cervical vertebrae produce an enormous tensile stress on the lambdoid sutures as a result of which the lambdoid suture has a prolonged patency.[24] In contrast, the number of muscles acting on the coronal and sagittal sutures is fewer such as the frontalis and temporalis. This explains the early obliteration of these sutures.[3]

The knowledge of suture patency has clinical implications in osteopathic medicine and biomedical science.[3] The prolonged patency of the lambdoid suture is also an important factor for normal autonomic functioning considering the fact that the vagus nerve passes through the jugular foramen which can get compressed in cases involving early suture obliteration.[25] The mechanism of suture obliteration is multifactorial and therefore still not understood completely. It depends on age, genetic factors, tensile stresses, and tissue interactions.[5],[6],[7] The role of TGF-β in cranial suture fusion is now conclusively demonstrated in physiological mouse models.[11] The tensile forces of the muscles and ligaments attached near the suture delay the obliteration of the suture.[3] Fibroblast growth factor signaling, bone morphogenetic protein signaling, Wnt signaling, polycystins, mechanical stimuli, and several signaling interactions influence suture obliteration.[26]

Suture closure is often used to determine the age of the individual.[27] The concept of increased suture closure with advancing age was understood in the 16th century.[28] Cranial sutures can be used as a tool for age determination in individuals aged between 30 and 60 years with accuracy in the range of 5–10 years.[29] Khandare et al. conducted a postmortem study on cranial sutures and observed that the ectocranial obliteration of the sutures is inconclusive for age estimation, whereas the endocranial obliteration is useful and more accurate. The authors reported complete closure of sagittal suture between 61 and 65 years, coronal suture between 56 and 60 years, lambdoid suture between 66 and 70 years, and temporoparietal suture between 66 and 70 years. The endocranial fusion of sagittal suture starts at the end of 26 years and completes itself by the age of 61–65 years. The endocranial fusion of coronal suture starts as early as 25–30 years and completes itself by the age of 56–60 years. The endocranial fusion of lambdoid suture starts at the age of 25–30 years and completes itself by the age of 66–70 years.[22],[30] In another study on suture closure involving 150 Indian skulls, it was observed that the obliteration occurs rapidly on the endocranial aspect and that the endocranial obliteration is more useful in age estimation than ectocranial obliteration.[31] Sahni et al. studied suture closure in 538 males and 127 females during autopsy in North West India. The authors reported that obliteration begins earlier in males than in females and is earlier on the endocranial aspect than ectocranial. The authors concluded that the phenomenon of suture obliteration is erratic and not useful for accurate age estimation.[32] In another study by Kumar et al. involving seventy autopsy cases in the third, fourth, and fifth decades of life, it was observed that endocranial fusion was more regular than ectocranial. The authors also concluded that suture closure is not useful for age estimation.[33] Some researchers are of the opinion that age estimation using sutures can only be given in a range of decades.[34] Most research studies conclude that the endocranial suture fusion is straighter, more uniform, rapid, and complete. In contrast, the ectocranial fusion is irregular, serrated, slower, and more incomplete.[35],[36],[37] In another radiological study involving 104 individuals, the sagittal, coronal, and lambdoid sutures were studied. The study concluded that if suture closure is completely absent, then the age of the individual is below 30, and if there is complete fusion of all the three sutures, the age of the individual is above 40 years.[38]

In our study, the age of the skull was not known. Moreover, the suture was studied only on the ectocranial aspect, and it was not observed as to whether the patency extends throughout the entire extent of the suture till the endocranial aspect. These were the limitations of the study, and the authors believe that there is a lot of scope for researchers to study suture obliteration more appropriately taking into consideration all factors. A literature review reveals that the endocranial obliteration is rapid, uniform, and more accurate for age estimation. The ectocranial obliteration is irregular, slow, and not accurate for age estimation. Future studies can also involve microscopic evaluation of sutures which can determine the extent of suture obliteration from ectocranial to endocranial aspect more accurately.


  Conclusion Top


In our study, we observed that the lambdoid sutures are more patent and less obliterated when compared to coronal and sagittal sutures. This is believed to be due to the larger number of muscles and ligaments of the cervical vertebrae attached to the lambdoid suture when compared to those of the coronal and sagittal sutures. The time of obliteration of sutures has immense clinical implications in neuroscience as early closure leads to craniosynostosis, impairing brain development. In contrast, a Grade 0 patent suture must be thoroughly evaluated by neurologists to assess the extent of patency and its clinical implications.

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Conflicts of interest

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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