In the

base of the skull The base of skull, also known as the cranial base or the cranial floor, is the most inferior area of the skull. It is composed of the endocranium and the lower parts of the calvaria. Structure Structures found at the base of the skull are for ...

, in the

great wings The greater wing of the sphenoid bone, or alisphenoid, is a bony process of the sphenoid bone; there is one on each side, extending from the side of the body of the sphenoid and curving upward, laterally, and backward. Structure The greater wi ...

of the

sphenoid bone The sphenoid bone is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the basilar part of occipital bone, basilar part of the occipital bone. The sphenoid bone is one of the seven bones ...

, medial to the foramen ovale, a small aperture, the sphenoidal emissary foramen, may occasionally be seen (it is often absent) opposite the root of the

pterygoid process The pterygoid processes of the sphenoid (from Greek ''pteryx'', ''pterygos'', "wing"), one on either side, descend perpendicularly from the regions where the body and the greater wings of the sphenoid bone unite. Each process consists of a me ...

. When present, it opens below near the

scaphoid fossa In the pterygoid processes of the sphenoid, above the pterygoid fossa is a small, oval, shallow depression, the scaphoid fossa, which gives origin to the Tensor veli palatini The tensor veli palatini muscle (tensor palati or tensor muscle of the ...

Vesalius Andreas Vesalius (Latinized from Andries van Wezel) () was a 16th-century anatomist, physician, and author of one of the most influential books on human anatomy, ''De Humani Corporis Fabrica Libri Septem'' (''On the fabric of the human body'' '' ...

was the first to describe and illustrate this foramen, and it thus sometimes bears the name of foramen Vesalii (meaning foramen of Vesalius). Other names include foramen venosum and canaliculus sphenoidalis.

Importance

If at all present, the sphenoidal emissary foramen gives passage to a small vein (vein of Vesalius) that connects the

pterygoid plexus The pterygoid plexus (;Entry "pterygoid"
in

with the

cavernous sinus The cavernous sinus within the human head is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica. Structure The cave ...

. The importance of this passage lies in the fact that an infected

thrombus A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of c ...

from an extracranial source may reach the cavernous sinus. The mean area of the foramen is small, which may suggest that it plays a minor role in the dynamics of

blood circulation The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

in the venous system of the head.

Structure

The sphenoidal emissary foramen varies in size in different individuals, and is not always present on both sides of the sphenoid bone (one on each great wing of the sphenoid). In a study conducted under 100 skulls, the sphenoidal emissary foramen was only present in 17% of the cases, and it was always single. 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 sphenoidal emissary foramen was present in 32.85% of the cases (20.0% right side, 12.85% left side). The incidence of bilateral and unilateral sphenoidal emissary foramen 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).
The skulls with one foramen were most frequent; those with two followed it and those with 3 (sphenoidal emissary) foramina were least frequent. Lang (1983) reported that the sphenoidal emissary foramen 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. 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.

Asymmetry

Though the sphenoidal emissary foramen 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 A carotid-cavernous fistula results from an abnormal communication between the arterial and venous systems within the cavernous sinus in the skull. It is a type of arteriovenous fistula. As arterial blood under high pressure enters the cavernous s ...

with drainage through the

emissary veins The emissary veins connect the extracranial venous system with the intracranial venous sinuses. They connect the veins outside the cranium to the venous sinuses inside the cranium. They drain from the scalp, through the skull, into the larger me ...

, and

neurofibromatosis Neurofibromatosis (NF) is a group of three conditions in which tumors grow in the nervous system. The three types are neurofibromatosis type I (NF1), neurofibromatosis type II Neurofibromatosis type II (also known as MISME syndrome – multi ...

. Thus, for the usually symmetric sphenoidal emissary foramina, asymmetry is more likely the result of a pathologic process than a normal variant. Ginsberg, Pruett, Chen and Elster did not find that asymmetry indicated disease in a study under 123 CT studies.

Importance

Structure

Asymmetry

References

See also