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
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
, into the larger
meningeal veins and
dural venous sinuses
The dural venous sinuses (also called dural sinuses, cerebral sinuses, or cranial sinuses) are venous channels found between the endosteal and meningeal layers of dura mater in the brain. They receive blood from the cerebral veins, receive cere ...
.
Emissary veins have an important role in selective cooling of the head. They also serve as routes where infections are carried into the cranial cavity from the extracranial veins to the intracranial veins.
There are several types of emissary veins including posterior condyloid, mastoid, occipital and parietal emissary vein.
Structure
There are also emissary veins passing through the
foramen ovale,
jugular foramen
A jugular foramen is one of the two (left and right) large foramina (openings) in the base of the skull, located behind the carotid canal. It is formed by the temporal bone and the occipital bone. It allows many structures to pass, including the ...
,
foramen lacerum
The foramen lacerum ( la, lacerated piercing) is a triangular hole in the base of skull. It is located between the sphenoid bone, the apex of the petrous part of the temporal bone, and the basilar part of the occipital bone.
Structure
The foram ...
, and
hypoglossal canal
The hypoglossal canal is a foramen in the occipital bone of the skull. It is hidden medially and superiorly to each occipital condyle. It transmits the hypoglossal nerve.
Structure
The hypoglossal canal lies in the epiphyseal junction between ...
.
Function
Because the emissary veins are valveless, they are an important part in selective brain cooling through bidirectional flow of cooler blood from the evaporating surface of the head. In general, blood flow is from external to internal but the flow can be altered by increased intracranial pressure.
Clinical significance
One notable emissary vein, the Vein of Vesalius, travels through the
sphenoidal emissary foramen
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 pr ...
inferior to the
zygomatic arch
In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygo ...
, connecting the
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 ...
. This is an important route for the spread of infection as
cranial nerve VI and the
internal carotid
The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these ...
pass through the cavernous sinus, with cranial nerves III, IV, V1, and V2 passing alongside the lateral wall of the sinus. Subsequent infection or inflammation in the cavernous sinus can result in septic
cavernous sinus thrombosis
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 ca ...
, with resultant damage to the cranial nerves contained within, as well as further spread of the infection leading to
meningitis.
Rupture of an emissary vein can result in a
subgaleal hemorrhage
Subgaleal hemorrhage, also known as subgaleal hematoma, is bleeding in the potential space between the skull periosteum and the scalp galea aponeurosis.
Symptoms
The diagnosis is generally clinical, with a fluctuant boggy mass developing over the ...
, a rare but serious injury most often seen as a complication of
vacuum extraction
Vacuum extraction (VE), also known as ventouse, is a method to assist delivery of a baby using a vacuum device. It is used in the second stage of labor if it has not progressed adequately. It may be an alternative to a forceps delivery and caes ...
.
See also
*
Occipital emissary vein
The occipital emissary vein is a small emissary vein which passes through the condylar canal
The condylar canal (or condyloid canal) is a canal in the condyloid fossa of the lateral parts of occipital bone behind the occipital condyle. Resectio ...
References
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Veins of the head and neck