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Sphenoid Bone Upper surface (foramen Vesalii labeled at left, fourth from bottom)
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Base of the skull Upper surface (Sphenoid is yellow, and foramen Vesalii is labeled at bottom of sphenoid)
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In the base of the
Skull , in the
Great Wings of the
Sphenoid Bone , medial to the
Foramen Ovale , a small aperture, the , may occasionally be seen (it is often absent) opposite the root of the
Pterygoid Process . When present, it opens below near the
Scaphoid Fossa .
Vesalius was the first to describe and illustrate the foramen that bears his name (foramen Vesalii meaning 'foramen of Vesalius'). The foramen Vesalii is sometimes referred to as the '''foramen venosum''', the '''sphenoidal emissary foramen''', or the '''canaliculus sphenoidalis'''.
If at all present, the foramen Vesalii gives passage to a small vein (vein of Vesalius) that connects the
Pterygoid Plexus with the
Cavernous Sinus . The importance of this passage lies in the fact that an infected
Thrombus from an extracranial source may reach the cavernous sinus.
1 The mean area of the foramen is small, which may suggest that it plays a minor role in the dynamics of
Blood Circulation in the venous system of the head.
2
The foramen Vesalii varies in size in different individuals, and is not always present on both sides of of the sphenoid bone (one on each great wing of the sphenoid). In a study conducted under 100 skulls, the foramen Vesalii was only present in 17% of the cases, and it was always single.
3
In another study, the differences between the right and the left side as well as the differences between the male and the female sex were noted. Out of the 70 sides observed (35 skulls total), the foramen Vesalii was present in 32.85% of the cases (20.0% right side, 12.85% left side). The incidence of bilateral and unilateral foramen Vesalii was 22.85% (8 out of 35 skulls) and 20% (7 out of 35 skulls) respectively. Regarding the differences between the male and the female sex, no remarkable differences were observed, although the occurrence of the foramen was more in females compared to males (found in 13 sides in females and in 10 sides in males).
4The skulls with one foramen Vesalii were most frequent; those with two followed it and those with 3 foramen Vesalii were least frequent (this was one of the conlusions in another study).
5 Lang (1983) reported that the foramen Vesalii was present in about 40% of his material. It was found on the right side in 49% of the cases and in 36% of the cases on the left.
6
In the newborn, the foramen is about 1.0 mm in length, in the adults at the right side about 2 mm and at the left side 1.4 mm. The width increases from 1.0 to 1.14 mm at the right side and from 1.0 to 1.3 mm at the left side.
7
Though the foramen Vesalii is small and variable, it is consistently symmetrical. In a study in which 50 high-resolution
CT Scans of the base of the skull were reviewed, the significance of asymmetry was investigated. In a large number of cases, the foramen was remarkably symmetric, and where there was asymmetry, it signified abnormality in four of the six cases. Abnormal causes of asymmetry included invasion by nasopharyngeal melanoma, angiofibroma,
Carotid-cavernous Fistula with drainage through the
Emissary Veins , and
Neurofibromatosis . Thus, for the usually symmetric foramen Vesalii, asymmetry is more likely the result of a pathologic process than a normal variant.
8 Ginsberg, Pruett, Chen and Elster did not find that asymmetry indicated disease in a study under 123 CT studies.
9
