Sphenoidal emissary foramen
Encyclopedia
In the base of the skull
, in the great wings of the sphenoid bone
, 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. When present, it opens below near the scaphoid fossa
. Vesalius
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.
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. 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.
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.
with drainage through the emissary veins
, and neurofibromatosis
. 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.
Base of the skull
The base of skull is the most inferior area of the skull, composed of the endocranium and lower parts of the skull roof.-Bones:*Ethmoid bone*Sphenoid bone*Occipital bone*Frontal bone*Parietal bone*Temporal bone**Petrous portion of the temporal bone...
, in the great wings of the sphenoid bone
Sphenoid bone
The sphenoid bone is an unpaired bone situated at the base of the skull in front of the temporal bone and basilar part of the occipital bone.The sphenoid bone is one of the seven bones that articulate to form the orbit...
, medial to the foramen ovale
Foramen ovale
There are multiple structures in the human body with the name foramen ovale :* In the fetal heart, the foramen ovale is a shunt from the right atrium to left atrium....
, a small aperture, the sphenoidal emissary foramen, may occasionally be seen (it is often absent) opposite the root of the pterygoid process. When present, it opens below near the scaphoid fossa
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.-External links:*...
. Vesalius
Vesalius
Andreas Vesalius was a Flemish anatomist, physician, and author of one of the most influential books on human anatomy, De humani corporis fabrica . Vesalius is often referred to as the founder of modern human anatomy. Vesalius is the Latinized form of Andries van Wesel...
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 plexusPterygoid plexus
The pterygoid plexus is a venous plexus of considerable size, and is situated between the temporalis muscle and lateral pterygoid muscle, and partly between the two pterygoid muscles.-Tributaries received:...
with the cavernous sinus
Cavernous sinus
The cavernous sinus , within the human head, is a large collection of thin-walled veins creating a cavity bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica.-Contents:...
. The importance of this passage lies in the fact that an infected thrombus
Thrombus
A thrombus , or blood clot, is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system...
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 in the venous system of the head.
Morphology and morphometry
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 fistulaCarotid-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...
with drainage through the emissary veins
Emissary veins
The emissary veins are valveless veins which normally drain external veins of the skull into the dural venous sinuses. However, because they are valveless, pus can flow into the skull through them as well, making them a possible route for transmission of extracranial infection to get into the...
, and neurofibromatosis
Neurofibromatosis
Neurofibromatosis is a genetically-inherited disorder in which the nerve tissue grows tumors that may be benign or may cause serious damage by compressing nerves and other tissues...
. 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.