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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 7  |  Issue : 2  |  Page : 93-96

Morphometric and topographic analysis of calvaria: A special focus on parietal emissary foramina


Department of Anatomy, Pondicherry Institute of Medical Sciences, Puducherry, India

Date of Submission08-Jul-2021
Date of Acceptance19-Sep-2021
Date of Web Publication30-Dec-2021

Correspondence Address:
Naga Jyothi Chigurupati
Department of Anatomy, Pondicherry Institute of Medical Sciences, Kalapet, Puducherry
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcrsm.jcrsm_57_21

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  Abstract 


Background: The parietal foramina (PFs) are located on either side of the sagittal suture at the posterior aspect of the parietal bone. The part of the sagittal suture between the two PFs is called obelion because it resembles the Greek symbol % “obelos.” The PF transmits an emissary vein named Santorini vein which connects the extracranial veins to the superior sagittal sinus. The emissary veins are of clinical significance as they are involved in the pathway of spreading infection from the extracranial to the intracranial source. PF is of special interest to neuroanatomists and neurosurgeons due to its anatomical variations and surgical importance.
Materials and Methods: A total of 111 dry human calvariae of unknown gender were included in the study. These human calvariae were observed for the presence or absence and also observed for the unilateral, bilateral, single, or multiple PFs. The foramina were macroscopically observed by using a magnifying lens, and a needle was probed into each foramen to check their patency. Topographical parameters were measured.
Results: Out of 111 calvariae, a single parietal emissary foramen was observed in 63 (56.7%) on the right parietal bone, 67 (60.3%) on the left parietal bone, and absence of parietal emissary foramen on right parietal bone in 41 (36.9%) and 37 (33.3%) on the left parietal bone, bilateral absence in 23 (20.7%) of the parietal bones. The presence of parietal emissary foramen on the sagittal suture was observed in 2 (1.8%) of skulls and also noted the single, double, multiple PF in 56.7%, 2.7%, 1.8% and 60.3%, 4.5%, 0, respectively. The different shapes of PF that was observed were circle shape on the right side 69.3%, on the left 66.6%, slit shape on the right 0.9%, on the left 1.8%, oval shape on the right 2.7%, on the left 1.8%. Out of all parietal emissary foramen, bilateral PF was observed in 53 + single parietal foramen on right 63 + on left 67 + double on right 3 + on left 5 + multiple on right 3 = 247. Out of 247 PF, 8 were patent through and the connection was oblique. All the other foramina were found to open into the diploic space. For those foramina through and through patency could not be assessed. The distance between the PF, distance of PF and sagittal suture, distance from the bregma to obelion, distance from lambda to obelion were measured. The obtained results are tabulated.
Conclusion: Parietal emissary veins are surgically important structures that receive little attention in scalp surgeries. These veins cause excessive bleeding if not located properly. The current study reports the anatomical variations in the PF which may serve as an important landmark to the neurosurgeon.

Keywords: Emissary foramen, obelion, parietal bone, parietal foramina, sagittal suture


How to cite this article:
Chigurupati NJ, Sriambika K, Muraleedharan A, Gunasegaran J P, Devi R. Morphometric and topographic analysis of calvaria: A special focus on parietal emissary foramina. J Curr Res Sci Med 2021;7:93-6

How to cite this URL:
Chigurupati NJ, Sriambika K, Muraleedharan A, Gunasegaran J P, Devi R. Morphometric and topographic analysis of calvaria: A special focus on parietal emissary foramina. J Curr Res Sci Med [serial online] 2021 [cited 2022 Jan 19];7:93-6. Available from: https://www.jcrsmed.org/text.asp?2021/7/2/93/334461




  Introduction Top


Anatomical studies have focused on the various foramina of the human skull including emissary foramina. The emissary foramina allow the passage of emissary veins that connect the intracranial venous sinuses with extracranial veins of the scalp.[1] Although these veins are valved, they allow the blood to flow in both directions. Under normal circumstances, blood flow through these veins is slow. However, in cases of increased intracranial pressure, the emissary veins become an important source of draining blood from the intracranial veins.[2] These veins also serve an important function of maintaining the intracranial pressure and can act as safety valves during cerebral congestion and obstruction of the internal jugular veins. The parietal emissary vein connects the superior sagittal sinus with the occipital vein, which then joins the vertebral venous plexus. Parietal emissary veins also interact with the diploic veins within the cranial bones.[3] The parietal foramina (PFs) are the openings in the skull vault which are located one on either side of the sagittal suture at the posterior aspect of the parietal bone. Because of resemblance to the Greek symbol “obelos” (÷) in which the line represents the sagittal suture and the dots represent the bilateral PFs, the name obelion is given to a bony point over sagittal suture which is just medial to the PFs.[4],[5],[6]

The cranial region around the PF is thought to be phylogenetically distinct where several anatomical bony variations and congenital anomalies can occur. The variations and anomalies have been documented to occur at the level of the obelion, the point on the posterior interparietal suture of the skull, and at a short distance in front of the lambda, where abnormal dilation of PFs is frequently observed.[7] Anatomical variations of foramina of the skull have been of interest for neuroanatomists due to the clinical consequences that these structures can cause, especially in areas as neurosurgery and dentistry. These anatomical variations tend to be neglected by clinicians and most are mentioned or described as “rare” or “occasional” in human anatomy books. However, the knowledge of three-dimensional topographic anatomy of skull structures and their morphometric values is necessary but not sufficient for performing a safe treatment, thus it is suggested that detailed knowledge of anatomical variations is essential for students in health areas who work on the head and neck.[1]


  Materials and Methods Top


The observational study was conducted in the department of anatomy. 111 adult human dried calvaria of unknown gender and age were included. The foramina were macroscopically observed by using a magnifying lens and a needle was probed into each foramen to check their patency. Following measurements were made (1) distance between the right and left parietal foramen, (2) distance between the sagittal suture and the parietal foramen on both sides, (3) distance from the bregma to the OBELION, and (4) distance from the lambda to the OBELION. The morphometric data of the present study were performed by using a measuring scale. Mean and standard deviation is calculated.


  Results Top


111 calvariae were examined. Single PF was found in 63 (56.7%) on the right parietal bone, 67 (60.3%) on the left parietal bone, and absence of parietal emissary foramen on right parietal bone in 41 (36.9%) and 37 (33.3%) on the left parietal bone, bilateral absence in 23 (20.7%) of the parietal bones [Figure 1]a, [Figure 1]b, [Figure 1]c. The presence of PF on the sagittal suture was observed in 2 (1.8%) skulls [Figure 2], and also noted the single, double, multiple PF in 56.7%, 2.7%, 1.8%, and 60.3%, 4.5%, 0, respectively [Figure 3]a and [Figure 3]b. The different shapes of the PF that was observed were circle shape on the right side 69.3%, on the left 66.6%, slit shape on the right 0.9%, on the left 1.8%, oval shape on the right 2.7%, on the left 1.8%. Out of 247 PF, 8 were patent through and the connection was oblique. All the other foramina open into the diploic space. For these foramina, patency could not be assessed. Distance between the PF was measured and it ranged from 8 mm to 14 mm, the distance of right PF from sagittal suture was 2 mm to 11 mm, the distance of left PF from the sagittal suture was 2 mm to 15 mm, distance from the bregma to obelion 7.2 cm to 13.2 cm, distance from lambda to obelion 1.2 cm to 5.2 cm were measured. It was observed that the most of the foramen were located at about 6–10 mm away from the sagittal suture. The maximum observed distance between obelion and bregma was between 8 and 10 cm and was seen in 29.7%–33.3%. The maximum observed distance between lambda and obelion was between 3.1 and 5 cm and present in 27.9%–33.3%.
Figure 1: (a) Unilateral single left parietal foramen, (b) Unilateral single right parietal foramen. (c) Bilateral absence of parietal foramen

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Figure 2: Parietal foramen on the sagittal suture

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Figure 3: (a and b) Multiple parietal foramina

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Results are tabulated in [Table 1], [Table 2], [Table 3], [Table 4], [Table 5].
Table 1: Number of parietal foramina (n=111)

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Table 2: The range of distance of the parietal foramina from the sagittal suture

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Table 3: Shape of foramina

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Table 4: The distance of the obelion from bregma

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Table 5: The distance from lambda to obelion

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The shape of the foramen also varied. The following shapes were observed, circular, oval, and slit. The percentages of the different shapes are tabulated in [Table 3].

Values are presented as numbers (%).


  Discussion Top


The PF is usually bilaterally located one on either side of the sagittal suture at the level of obelion, but it can be absent or present unilaterally also. Incidence of the presence of foramina ranges from 50% to 80% in different groups and also shows variations in their shape, size, number, and location.[1],[5],[8] According to Boyd, unilateral PF is seen more commonly on the right side than on the left (20.7%:15.2%), but in the present study, unilateral foramen is seen more commonly on the left side than right (56.7%:60.3%).[9]

The prevalence of PF was shown to be higher by Murlimanju et al. as compared to that of several other studies. Yoshioka et al. explained that the difference is due to the ossification process of the anterior fontanelle.[8] The distance of the foramen from the sagittal suture was ranged from 0.5 mm to 1.3 mm and 1 mm to 1.5 mm on the right and left side, respectively, measured by a divider and measuring scale as observed by Murlimanju et al.[4] In the present study, the range on the right side was 5 mm to 13 mm and the left from 1 mm to 15 mm measured by measuring scale, and the presence of PF on the sagittal suture [Figure 2] in 1.8% is low in the present study when compared with the 5.9% and 3.4% by Boyd and Murlimanju et al.,[4] respectively.

It is also reported that the PF varies in its shape such as circular, oval, or fissure.[9],[10] In the present study also, the different shapes that were observed were circular shape 69.3% on right, 66.6% on left, oval shape 2.7% on right, 1.8% on the left, and also observed small slit in 0.9%.

A study by Boyd observed that the PF is larger in Australian and New Zealand people than the other races.[9] The possibility of an enlarged PF should be kept in mind during the clinical examination and surgical procedures. The emissary foramina and the diploic veins of the skull which are involved in the spread of infection from the extracranial veins to intracranial sinuses show important relationships. The infection at the diploic, meningeal, and cerebral veins which communicate along with the emissary veins can cause complications of osteomyelitis of the cranium and vault, meningitis, cerebral abscess.[9] Knowledge of this enlarged PF is important because it is associated with many pathological conditions such as cerebral venous and cortical anomalies and skull fractures.[11]

The present study is of immense help to the radiologists to differentiate PF from pathological conditions like lytic lesions and the burr holes caused by the neurosurgical procedures as PFs usually have a well-defined margin. Thorough knowledge of the morphological variation will be of significant help for the neurosurgeons to perform safe radical surgery.[12] The misinterpretation would lead to complications such as bleeding and treatment failure.


  Conclusion Top


PFs are surgically important structures that receive surprisingly little attention in scalp surgeries. The emissary veins passing through these foramina cause excessive bleeding if not located properly. The current study has reported the anatomical variations in the PF which may be useful for radiologists, neurosurgeons, and anatomists.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Freire AR, Rossi AC, de Oliveira VC, Prado FB, Caria PH, Botacin PR. Emissary foramens of the human skull: Anatomical characteristics and its relations with clinical neurosurgery. Int J Morphol 2013;31:287-92.  Back to cited text no. 1
    
2.
Reis CV, Deshmukh V, Zabramski JM, Crusius M, Desmukh P, Spetzler RF, et al. Anatomy of the mastoid emissary vein and venous system of the posterior neck region: Neurosurgical implications. Operative Neurosurgery 2007;61:193-200.  Back to cited text no. 2
    
3.
Mortazavi MM, Tubbs RS, Riech S, Verma K, Shoja MM, Zurada A, et al. Anatomy and pathology of the cranial emissary veins: A review with surgical implications. Neurosurgery 2012;70:1312-9.  Back to cited text no. 3
    
4.
Murlimanju BV, Saralaya VV, Somesh MS, Prabhu LV, Krishnamurthy A, Chettiar GK, et al. Morphology and topography of the parietal emissary foramina in south Indians: An anatomical study. Anat Cell Biol 2015;48:292-8.  Back to cited text no. 4
    
5.
Fating A. Sudhir Pawar Parietal foramina in adult human skulls: An anatomical study. medicainnovatica.2020;9:46-9.  Back to cited text no. 5
    
6.
Currarino G. Normal variants and congenital anomalies in the region of the obelion. AJR Am J Roentgenol 1976;127:487-94.  Back to cited text no. 6
    
7.
Tsutsumi S, Nonaka S, Ono H, Yasumoto Y. The extracranial to intracranial anastomotic channel through the parietal foramen: Delineation with magnetic resonance imaging. Surg Radiol Anat 2016;38:455-9.  Back to cited text no. 7
    
8.
Yoshioka N, Rhoton AL Jr., Abe H. Scalp to meningeal arterial anastomosis in the parietal foramen. Neurosurgery 2006;58:S123-6.  Back to cited text no. 8
    
9.
Boyd GI. The emissary foramina of the cranium in man and the anthropoids. J Anat 1930;65:108-21.  Back to cited text no. 9
    
10.
Mann RW. Enlarged parietal foramina and craniosynostosis in an American Indian child. AJR Am J Roentgenol 1990;154:658.  Back to cited text no. 10
    
11.
Reddy AT, Hedlund GL, Percy AK. Enlarged parietal foramina: Association with cerebral venous and cortical anomalies. Neurology 2000;54:1175-8.  Back to cited text no. 11
    
12.
Berge JK, Bergman RA. Variations in size and in symmetry of foramina of the human skull. Clin Anat 2001;14:406-13.  Back to cited text no. 12
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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