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The veins of the centralnervoussystem drain deoxygenated blood from the cerebrum, cerebellum, brainstem and spinalcord. After emptying into the duralvenoussinuses, most cerebral venous blood flows into the internaljugularveins before it is returned to the heart. This article discusses the venous drainage of the brain and relevant clinical conditions such as cavernous sinus thrombosis.
Veins draining the brainparenchyma may be divided into superficial and deepveins. The superficialveins primarily drain the cerebralcortex, whereas the deepveins drain the deepstructures within the hemispheres. These veins do not typically follow the arterial supply and there is significant variation in anatomy between different subjects. Another notable feature of cerebralveins is that they lackmuscularwalls and valves.
The cerebralveins empty into the duralvenoussinuses situated within the subarachnoidspace. The superficialsystem drains into the superiorsagittalsinus, while the deepsystem drains into transverse, straight and sigmoidsinuses.
The superficial venous system comprises:
The cortical venous system is further divided into superior, middle and inferior groups.
There are several important superficial cerebral veins:
Superior anastamotic vein of Trolard
Superficial middle cerebral vein (Sylvian vein)
Inferior anastomotic vein of Labbé
Inferior anastomotic vein of Labbé
The vein of Labbé connects the superficialmiddlecerebralvein with the transversesinus. The location of this vein is extremely variable, making it vulnerable to injury during craniotomy procedures.
Superior anastomotic vein of Trolard
The superior anastomotic vein of Trolard connects the superiorsagittalsinus with the superficialmiddlecerebralvein. It is usually the smallest of the three superficial veins mentioned in this article.
Superficial middle cerebral vein
The superficial middle cerebral vein is also known as the Sylvian vein, and it usually courses along the Sylvianfissure (lateral sulcus) picking up veins from the surrounding operculum (brain region surrounding the lateral sulcus) as it runs postero-anteriorly. The superficialmiddlecerebralvein then drains into the cavernoussinus after curving around the anteriortemporallobe.
The deepcerebralvenousdrainagesystem comprises:
Deep cerebral veins:
This system drains the thalamus, hypothalamus, internalcapsule, septumpellucidum, choroidplexuses, corpusstriatum, and the whitematter.
Internal cerebral veins
This pair of veins originate at the foramenofMunro (interventricular foramen) and run posteriorly within the roof of the thirdventricle. The twointernalcerebralveins eventually anastomose to form the GreatveinofGalen.
The two basalveins are closely related to the midbrainstructures and drain into the great vein of Galen (great cerebral vein). The origin of these veins lies close to the anterior perforated substance.
A number of striateveins drain the caudatenucleus, thalamus, corpusstriatum, and internalcapsule, returning blood to the internalcerebral and basalveins. The superiorstriateveins empty into the internalcerebralveins, while the inferiorstriateveins empty into the basalveins.
Great cerebral vein
The two internalcerebralveinsunite to form the greatcerebralvein before it passes beneath the corpuscallosum and anastomoses with the straightsinus. As well as the internalcerebral and basalveins, it receives blood from the corpuscallosum itself, as well as the occipitallobes.
Dural venous sinuses
The duralvenoussinus layers lie between the outer (periosteal) and inner (meningeal) layers of the duramater (see Figure 4). Cerebralveins discussed above drain blood into the sinuses and follow a course through the duralvenoussinussystem eventually meeting the internaljugularveins (see Figure 5). There are novalves within the sinuses. The falxcerebri contains the superior and inferiorsagittalsinuses, as well as the straightsinus. The sinuses anastomose at the confluenceofsinuses at the anatomical landmark of the internaloccipitalprotuberance.
The inferiorsagittalsinus meets the greatcerebralvein before continuing as the straightsinus. The transversesinuses emerge from the confluence and go on the form the sigmoidsinuses, which drain into the internaljugularveins as they leave the cranium via the jugularforamina. The cavernoussinus is located anteriorly, and receives blood from the ophthalmicveins before emptying into the superior and inferiorpetrosalsinuses and subsequently the internaljugularveins.
Clinical relevance: Cavernous sinus thrombosis
Anatomically, the cavernoussinus is closely related to the highly anastomotic system of nasalsinuses, which can result in the retrograde spread of infection. The causative organism is usually Staphylococcus, Streptococcus or Haemophilus species. ¹
Common causes include: ²
Nasal furuncle (boil) [50%]
Sinus infection (sphenoid, ethmoid) [30%]
Dental infections [10%]
Cavernoussinusthrombosis is also a rare but potentially lethal complication of orbitalcellulitis. ³
Clinical relevance: Cerebral venous thrombosis
This describes a situation wherein a clot has formed within the duralvenoussinuses.
Signs and symptoms can mimic stroke presentation, and include:
Headache (can be similar to that described in subarachnoid haemorrhage i.e. sudden blow to the head)
Seizures, status epilepticus (common in first few days of onset) 4
Common causes include infection spreading from the frontalsinuses, subduralempyema (Staphylococcus aureus is the most common organism), trauma, surgery, pregnancy, and the combinedoralcontraceptivepill.
Recommended treatment is anticoagulation with heparin, followed by warfarin, to reach INR target 2 – 3. 5 Rarely, surgicalintervention may be required to evacuate the clot.
The superior and inferiorcerebellarveins drain this region. The former empties into the transverse, straight, and superiorpetrosalsinuses, and the latter drains into the sigmoid, inferiorpetrosal, occipital and straightsinuses.
Deoxygenated blood is drained from the midbrainregion as it empties into the greatcerebral and basalveins. Inferiorly, veins drain blood from the pons and medulla into the superior and inferiorpetrosalsinuses, as well as the transverse and occipitalsinuses.
In this article, we have discussed the major vessels draining venous blood from the brain – the IJVs.
There is a second system that assists in cerebral venous drainage. It is known as the vertebral venous plexus (VVP), and can be divided into one plexus lying inside (internal) the vertebral column, and one lying outside (external) the vertebral column.
Physiologically, the IJVs are capable of draining 100% of cerebral venous outflow, while the VVP can drain up to 30%.
The inferior petrosal sinus is a vessel that is fed by the majority of the veins in the posterior cranial fossa, such as the superficial and deep brainstem and cerebellar veins. The inferior petrosal sinus is a conduit between the IJVs and the VVP, meaning that blood from the posterior fossa can be drained by either system.
As we have discussed, we know that cerebral veins do not contain valves and are quite muscular structures. However, the IJV is an extremely thick, muscular vein – atypical when compared to other veins (it even retracts back into the skull when dissected close to the jugular foramen). This muscular wall suggests two things:
It is under the control of the sympathetic and parasympathetic nervous systems by way of adrenergic and cholinergic smooth muscle tone; and
It plays an important role in cerebral perfusion pressure control.
It is widely accepted that when lying supine, the IJVs remain patent, but their patency reduces upon erect sitting or standing, where it closes completely. This loss of patency is driven by the pressure exerted on the veins by the tissue surrounding them.
Thus, when sitting or standing, our IJVs are closed, and blood ‘backfills’ into the inferior petrosal sinus and posterior fossa veins while the VVP attempts to compensate for the sudden increase in venous load. Eventually, the intracranial venous pressure exceeds the perijugular tissue pressure, and the IJVs open to allow venous return toward the heart (until the tissue pressure again exceeds the venous pressure, after which the IJVs close again). This cycle continues throughout periods of erect sitting and standing. But what does this mean clinically?
When assessing the jugular venous pressure, we use the internal jugular vein as a surrogate for cardiac function at 45o for two reasons:
It has no valves: it is a relatively good representation of what is occurring in the right heart; and
It is normally empty: any blood ‘regurgitating’ back into the IJV is causing the IJV to open in what is normally a closed vessel, greatly exaggerating the appearance of the JVP waveform.
If it wasn’t for the dual cerebral venous outflow and having IJVs that normally remain closed in sitting and standing positions, it is likely that we wouldn’t be able to use JVP as a surrogate marker for cardiac function.
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Varshney S, Malhotra M, Gupta P, Gairola P, Kaur N. Cavernous sinus thrombosis of nasal origin in children. Indian J Otolaryngol Head Neck Surg 2015;67:100-5.