Dural venous sinuses and neighbouring structures.
Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the dural venous sinuses. Now, in this tutorial, we will not only be looking at the venous sinuses but we will also be looking at the veins that drain into these venous sinuses. Also, we're going to look at arteries and other structures that are seen in relation to the dural venous sinuses at the base of the skull.
Now, here on this image, you can see – this is one of the images that you're going to be seeing throughout this tutorial and what we're doing here is just cutting the skull and looking at it from a superolateral view so we can now see all these structures here that we're going to be describing. The cerebral venous system is somewhat different with that of the rest of your body. Now, this happens since the veins of the brain they don't follow even remotely the arteries. The veins of the brain, they emerge from the cortex and subcortical areas and they lie in the subarachnoid space coursing over the surface of your brain then aggregating into larger channels until they pierce the arachnoid mater and the meningeal layer of the dura mater and drain into then the dural venous sinuses. So, the whole system may be divided into two sections that we will talk about: the cerebral veins and also the dural venous sinuses.
We're going to, however, focus more on the dural venous sinuses here on this tutorial – just see a few cerebral veins. The dural venous sinuses are actually venous channels that are formed between the two layers of the dura mater – the meningeal and the periosteal. And we start with the first one which we see here highlighted in green which is the superior sagittal sinus and we're looking now at an image of the superior view of the base of the skull where you see then all the structures – a lot of the structures – we're going to talk about. And here a little bit of the superior sagittal sinus just cut and highlighted in green. You can also see the superior sagittal sinus from this image of the skull here highlighted in green.
Now, the superior sagittal sinus is one of the two sinuses that occupies the longitudinal cerebral fissure. It is an unpaired sinus and the most superficial of the two sinuses occupying this part of the brain and residing also in the base of the falx cerebri. And, as the name suggests, it runs in a sagittal plane from the anterior aspect of the falx cerebri to its termination at the confluence of the sinuses at the occipital protuberance as you can see here on this illustration a bit better. And as you can see now in this illustration here with the brain and the superior sagittal sinus highlighted – we're looking at it from a lateral view – where we see that the superior sagittal sinus actually receives venous blood from many – as you can see here – all these cortical superficial veins.
The next one we're going to be seeing here now back to this image is known as the inferior sagittal sinus. This is also known as the second sagittal sinus which is located deep to the superior sagittal sinus. Now, it is located in the free border of the falx cerebri just dorsal to the corpus callosum and is also an unpaired sinus. And as you can see here on this image going back to show you this image – you notice now the inferior sagittal sinus highlighted in green – it starts from the region just above the cribriform plate – around here – so, cribriform plate of the ethmoid bone and as you can see on this image extends to the anterior midline of the tentorium cerebelli so then terminating in the straight sinus which is right about here. This sinus is smaller than the superior sagittal sinus and receives blood from the falx itself and medial aspects of the cerebral hemispheres – and you can see here now the medial aspect of the brain and you can also see then the inferior sagittal sinus highlighted and here the one that we talked about before, this is the superior sagittal sinus.
We just saw that the inferior sagittal sinus terminates at this structure here that you see now highlighted – the straight sinus. The straight sinus is a midline structure that lies within the posterior end of the falx cerebri and the middle of the tentorium cerebelli. And looking at this image here, you can see that it begins at the great cerebral vein and also the inferior sagittal sinus here which you can also see here. And then it proceeds here to pass through the confluence of sinuses where it terminates at the level of the internal occipital protuberance. The straight sinus can also be seen here on this image that you can see the full straight sinus from a medial view of the brain. And here, you can also see clearly how it begins as the confluence, or connection here, of the great cerebral vein and also the inferior sagittal sinus coming together then to form the straight sinus that will then terminate here at the confluence of sinuses.
Another vein that drains the cerebrum and empties into the straight sinus is this one that you see here now highlighted in green from the base of the skull – this vein here – this is cut and this is the great cerebral vein. The great cerebral vein is a short vein that is formed by the union of the left and right internal cerebral veins and it drains into the straight sinus. You can also see it here on this image clearly and you even notice here how it drains into the straight sinus. The three sinuses that I have discussed so far namely the superior, the inferior sagittal and the straight sinus together with the short sinus, the occipital sinus, form the site of union you see here highlighted in green known as the confluence of sinuses. Simply put, it is the site of the union of the superior sagittal sinus, the straight sinus, the occipital sinus and the transverse sinuses – all at the level of the internal occipital protuberance. So, as you can see here as I mentioned before, you see here the superior sagittal sinus, the straight sinus, the transverse sinuses clearly represented here. You can also see here the confluence of sinuses from this view of – the lateral view of – the brain highlighted in green.
Two sinuses namely the left and right transverse sinuses begin from the confluences of sinuses. So, we're looking now at the left and right transverse sinuses. And, as you can see on this image, the transverse sinuses travel at the base of the tentorium cerebelli along the occipital bone. The transverse sinus also communicates with the straight sinus which you see a little bit here on this image and the occipital sinus at the level of the internal occipital protuberance. Receives tributaries from the inferior cerebral vein and the inferior anastomotic vein of Labbé as well as from the sinuses that terminate in the confluence of sinuses and finally drains into the sigmoid sinus. You can also see here on this image the transverse sinus, or one of them, specifically the left one highlighted in green.
The next image that we're going to be highlighting here – next structure – is showing the sigmoid sinus. The sigmoid sinus is a paired sinus that is continuous with the transverse sinus anteriorly and courses along the floor of the posterior cranial fossa to enter the jugular foramen. The sigmoid sinuses are S-shaped sinuses and, just after they receive blood from the superior and inferior petrosal sinuses, they form the jugular bulb that will enter the jugular foramen along with the ninth, tenth, eleventh cranial nerves as the internal jugular vein. We can also see here on this image of the brain the sigmoid sinus highlighted in green specifically the left one.
So far, we have looked at the venous sinuses located in the upper and posterior part of your brain and these sinuses empty into the sigmoid sinus and finally into the internal jugular vein. Now, let's have a look at the sinuses of the most anterior and basal part of the brain. Starting with the sphenoparietal sinus which you can see here highlighted in green. The sinus passes along the free border of the lesser wing of the sphenoid. It drains into the cavernous sinus and receives tributaries on either side from the superficial middle cerebral vein which aids in draining blood from the cerebral hemispheres and optic part of the frontal lobe. You can also see here the sphenoparietal sinus highlighted in green from this image.
The next structure we're going to be highlighting now is known as the cavernous sinus. This one is a spongy venous space located on both sides of the sella turcica which is found right about here. So, if we were to remove all these structures, you would see that the sella turcica is located right about here on your skull. So, they are located on both sides of the sella turcica into which the ophthalmic veins and the sphenoparietal sinus open. This paired sinus also facilitates the passage of many structures to the superior orbital fissure and the foramen rotundum and these structures are the oculomotor nerve, the trochlear nerve, the ophthalmic and maxillary divisions of the trigeminal nerve, the abducens nerve, and the cavernous part of the internal carotid artery. And you can see all these structures passing through it on this area here where we just cut and remove a bit of the cavernous sinus. You can also see here the cavernous sinus on this image of the skull highlighted in green.
We have just looked at the cavernous sinus, now let's look at the intercavernous sinus. The intercavernous sinuses are connections between the left and right cavernous sinus that lie in the anterior and, in this case of our illustration, in the posterior borders of the diaphragma sellae. We can also see it from this view here of the skull – the posterior intercavernous sinus highlighted in green.
Next structure we're going to be highlighting is known as the superior petrosal sinus. Blood from the cavernous sinus drains into the inferior and superior petrosal sinuses. And the superior petrosal sinus – which you can see here – travels along the upper margin of the petrous part of the temporal bone in the superior petrosal sulcus and finally empties into the sigmoid sinus which if you remember you can also see it here on this image. You can also see here the superior petrosal sinus from this image.
The next one we're going to be talking about is now then the inferior petrosal sinus seen here on this magnified image. And the inferior petrosal sinus also drains from the cavernous sinus and goes to join the sigmoid sinus to form the internal jugular vein. It courses along the posterior lower margin of the petrous part of the temporal bone within the inferior petrosal sulcus to the jugular foramen. The inferior petrosal sinus receives tributaries from the internal auditory veins as well as from the veins of the medulla oblongata, pons and the inferior surface of the cerebellum. And on this image, you can see a little bit better on how the inferior petrosal sinus goes to then join the sigmoid sinus to form then the – you can see better on this side then – the internal jugular vein.
The sinuses that we have just described thus far, the cavernous sinus, the intercavernous sinuses and the superior and inferior petrosal sinuses are paired sinuses and the two corresponding sinuses of each side are connected with a venous plexus called the basilar venous plexus – seen here highlighted in green. The basilar venous plexus is located on the clivus over the basilar part of the occipital bone and is comprised of many interconnected venous channels between the layers of the dura mater. You can also see here on this image, the basilar venous plexus. As we have already seen, the sinuses of both the superior and posterior and anterior basilar part of the brain finally empty into the sigmoid sinus which we can say is the meeting point of deoxygenated blood in the brain.
Now, the continuation of the sigmoid sinus – as you can see here – this is, this structure that you see now highlighted in green, this is the continuation of the sigmoid sinus which is a large paired vein known as the internal jugular vein. This paired vein extends from the jugular foramen of the venous angle. It is the main vein of your neck that drains blood from the brain, superficial parts of the face, and neck.
On the next slide, I would like to show you schematically the flow of deoxygenated blood through the venous sinuses. First, we have on the top here these three, these are the veins that will then drain into the different sinuses that we have now listed below. Now, the superior cerebral vein draining into the superior sagittal sinus, the great cerebral vein into the straight sinus, the veins of the medial aspect of the hemisphere will be draining into the inferior sagittal sinus. If you remember well, the inferior sagittal sinus will be draining into the straight sinus while the straight sinus will be draining into the confluence of sinuses and the superior sagittal sinus will also be then draining into the confluence of sinuses. After that, deoxygenated blood will be going from the confluence of sinuses into the transverse sinus and also a reminder adding here the middle cerebral vein which is another vein that will be draining into the cavernous sinus then from the cavernous sinus also into the inferior petrosal sinus and the superior petrosal sinus. And the inferior petrosal sinus, superior petrosal sinus and the transverse sinus will then be draining into – deoxygenated blood – into the sigmoid sinus. And after that if you remember, the sigmoid sinus or the blood from the sigmoid sinus will then go into the internal jugular vein and follow its path all the way to the heart and then lungs for gas exchange.
Now, that we have covered the dural venous sinuses, let's move on and look at the other structures that can be seen in relation to these sinuses starting with the superior ophthalmic vein that you see here now highlighted in green. This vein begins medially above the eyeball which you can see a little bit here on this image and passes through the superior orbital fissure draining into the cavernous sinus.
Next, we see the superficial middle cerebral vein which begins at the lateral surface of the cerebral hemispheres and is one of the tributaries of the cavernous sinus. It runs along the lateral surface of the cerebrum to then open into the cavernous sinus. We can also see it here from this view – here a bit of magnification – to show the cut superficial middle cerebral veins.
The next structures we're going to be highlighting here on this image are known as the inferior cerebral veins. Now, they drain the undersurface of the cerebral hemispheres and they are mainly superficial veins depending on the part of the hemisphere that they drain. They empty into then the cavernous or the transverse sinuses.
So far, we have covered the dural venous sinuses and the venous vessels that drain into them. Now, let's look at this one that we see here highlighted in green which happens to be an artery – the internal carotid artery – which is one of the two branches that arises from the bifurcation of the common carotid artery. It is just – as a reminder – a paired artery found on either side of your head and neck giving off several branches, supplies oxygenated blood to the brain. In our illustration, we can see the cavernous segment of the internal carotid and, in this segment, is surrounded by the cavernous sinus as it enters the cranial vault through the carotid canal at the base of the skull and you can see that we even cut here a piece of the cavernous sign to then expose a bit more of the internal carotid artery.
The next structure we can see here is known as – is located also on the base of the skull in the middle cranial fossa to be more specific – which is then the optic chiasm. The optic chiasm, the fibers that come from the nasal sides of each retina, cross over to the opposite side of the brain while the fibers from the temporal side remain uncrossed. The term chiasm comes from the Greek word meaning "crossing".
Another structure that we see here highlighted in green is the trigeminal nerve – also at the base of the skull – and, as you know, the trigeminal nerve is the fifth cranial nerve and has three divisions: an ophthalmic branch or also known as the ophthalmic nerve, maxillary branch also known as the maxillary nerve, and a mandibular branch also known as then the mandibular nerve. Now, the branches of this nerve provide sensory innervation to your skin of the anterior part of your head specifically, also oral and nasal cavities, your teeth and the meninges. And, in addition, the mandibular division also carries motor fibers to the muscles of mastication.
The final structure we're going to look at now seen here highlighted in green is the pituitary gland. Pituitary gland which is also known as the hypophysis, is a small pea-sized bulb that extends from the hypothalamus at the base of your brain. It is an endocrine gland that regulates the activity of the six other major endocrine glands that release hormones integral or very important for growth and development. Now, this gland rests in the hypophyseal fossa of the sella turcica in the superior part of the sphenoid bone.
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