|Year : 2011 | Volume
| Issue : 1 | Page : 14-16
Morphological variations of a jugular foramen in North Indian human adult skulls
Ruchira Sethi, Vishram Singh, Nisha V Kaul
Department of Anatomy, Santosh Medical College, Ghaziabad, NCR-Delhi, India
|Date of Web Publication||11-Oct-2011|
J-41, Patel Nagar-I, Ghaziabad, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Aims: To assess the size and bridging patterns of jugular foramina of adult human skulls. Materials and Methods: The study was conducted on 56 adult North - Indian skulls procured from Department of Anatomy of Santosh Medical College, Ghaziabad. The jugular foramina were observed by naked eye and with magnifying lens to assess the variations in size and bridging patterns. Results: The jugular foramen was larger on the right side in 53.5% skulls and on the left side in 7.1% skulls. In the remaining skulls (39.4%) it was equal on both sides. Complete tripartite division was observed in 10.7% cases. Incomplete division was seen in 7.1% cases on right side and 3.5% cases on the left side. Incomplete division was never observed bilaterally. An additional accessory foramen was observed to be communicating with posterior condylar canal. Conclusion: The variations observed in present study are of immense value to ENT surgeons while performing middle ear surgeries for various jugular foramen tumors. Also, the bridging patterns cause compression to structures passing through this foramen hence accentuating the clinical presentations of Glomus jugulare.
Keywords: Glomus jugulare, Jugular foramen, Middle ear, Vernet′s syndrome
|How to cite this article:|
Sethi R, Singh V, Kaul NV. Morphological variations of a jugular foramen in North Indian human adult skulls. Indian J Otol 2011;17:14-6
| Introduction|| |
The morphological variants of skull foramina have aroused the curiosity of various research workers for many decades because of their clinical, surgical, anthropological, and racial significance.
A jugular foramen has always attracted attention of radiologists, ENT, and neurosurgeons because of recent advances in surgical procedures involving middle ear and skull base (Gray's anatomy).  Most textbooks of anatomy describe a jugular foramen as being located in posterior cranial fossa at the posterior end of petro-occipital suture. It is formed by the petrous temporal bone anterolaterally and the occipital bone posteromedially. Classically it is described as being divided into three compartments; anteromedial compartment lodging inferior petrosal sinus; intermediate compartment giving passage to glossopharyngeal, vagus and accessory cranial nerves; posterolateral compartment lodging sigmoid sinus which continues to the exterior as internal jugular vein. 
The compartmentalization of the foramen could be the logical reason for compression on the structures passing through it, specially the last four cranial nerves, causing varied symptoms grouped as jugular foramen syndrome (Vernet's Syndrome).
Most of the time these bridging patterns are not evident in a skull specimen. The present study set forth to assess the incidence of size variation, bridging pattern, and associated accessory foramen of a jugular foramen.
| Materials and Methods|| |
A total of 56 dry human adult skulls were examined. The skulls were of North-Indian origin. They were procured from Department of Anatomy of Santosh Medical College, Ghaziabad, UP. The foramina were observed macroscopically by the naked eye and with help of magnifying lens. The measurements were taken with help of Vernier Calipers. The size differences on the right and left sides were analyzed. The presence or absence of bony bridging was assessed and associated accessory foramina in this region were also observed. All the observations were recorded and results tabulated.
| Results|| |
The jugular foramen was larger on the right side in 53.5% of skulls and on the left side in 7.1% of cases [Table 1]. In the remaining (39.4%) it was equal on both sides [Figure 1].
|Figure 1: Basal view of a skull showing the right foramen greater than the left foramen|
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The incidence of bony bridging of a foramen revealed the presence of septation in 17.8% skulls on the right side and in 14.3% skulls on the left side [Table 2]. The classical description of tripartite septation was seen in 13% skulls bilaterally [Figure 2].
|Figure 2: Cranial view of a skull showing a complete tripartite division of the jugular foramen|
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Incomplete septation was always seen unilaterally [Figure 3]. It was obvious on the right side in 7.1% skulls and on the left side in 4.3% skulls only [Table 3]. The opposite sides of these six skulls did not even show the presence of any spine or tubercle like elevation.
|Figure 3: Cranial view of a skull with an incomplete bridging pattern showing two compartments|
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In 3.6% skulls, an additional accessory foramen was observed in the posteromedial wall of the jugular foramen on the left side only. This foramen was found to be communicating with the posterior condylar canal as observed by passing a thin probe through it.
| Discussion|| |
A Glomus jugulare tumor grows in and around the jugular foramen. This is the region where the jugular vein, 9 th , 10 th , and 11 th cranial nerves exit from the skull. These tumors cause compression of the structures within the foramen which leads to loss of hearing and paralysis of lower cranial nerves. A complete otological and neurological examination must be done keeping in mind the complex anatomy of a jugular foramen.
In the present study, a sincere effort has been made to study the complex anatomy of the jugular region. On the right side, a jugular foramen was found to be larger than the left. This goes well with the fact that right internal jugular vein is larger than the left in most of the individuals. The larger superior saggital sinus continues in succession as right transverse sinus, right sigmoid sinus, and right internal jugular vein, on the other hand the smaller inferior saggital sinus continues in succession as straight sinus, left transverse sinus, left sigmoid sinus and into left internal jugular vein. However, there is a wide variation in the anatomy of the intracranial venous sinuses, , which accounts for variation in size of a foramen. A little higher incidence of 61.4% was observed by Ekinci et al.  Wysocki et al,  gives an asymmetry between right and left foramina with an average ratio of 1.6. The variation of shape and size from side to side in same crania and in different cranium could be the result of different sexual or age stature. ,
The frequency of bridging pattern was more on the right side. The course of cranial nerves within the foramen presents many anatomical variations, depending upon the bridging pattern and its types. Tekdemir et al,  observed no partitions in their studies while Ekinci et al,  found bony bridging in 20% and tripartite foramen in 0.7%. Hatiboglu and Anil  (vide supra) studied 300 Anatolian skulls and observed complete septation on the right side in 5.6%, on the left side in 4.3%; partial septation on the right side in 2.6%, on the left side in 19.6%. Patel and Singel  studied the Indian Saurashtra region population to observe complete septation on the right side in 23.1%, on left side in 17.6%; partial septation on the right side in 49.5%, on the left side in 59.3%. This observation went in a wide difference with the present study suggesting racial factors involved in bridging patterns. None of the previous studies observed bilateral complete septation of the foramen.
Glomus jugulare tumors are found in the tunica adventitia of jugular bulb beneath the floor of middle ear or in relation to the tympanic branches of glossopharyngeal and vagus nerves in the middle ear. The compartmentalization may accentuate the clinical presentation of the glomus tumor. In early stages such patients visit an ear, nose, and throat surgeon, whereas in later stages patients with large intra-cranial extensions approach neurosurgeons.
In addition to the above findings an accessory foramen was found in the posteromedial wall of the jugular foramen communicating with posterior condylar canal. This may provide a potential source of communication of extra-cranial veins in the occipital region with sigmoid sinus. This channel can cause spread of infection from the region of scalp to intracranial venous sinus, leading to thrombosis.
Therefore, the knowledge of complex anatomy of the jugular region is of utmost importance to the ENT surgeons.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]
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