NA12- Brain Blood Supply PDF

Pag. 1 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem #14- 30.11.2021 Vascular supply to the cerebral hemisphere and brainstem Prof. Dellavia – 30/11/2021 – Author: Cam...

Pag. 1 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem #14- 30.11.2021 Vascular supply to the cerebral hemisphere and brainstem Prof. Dellavia – 30/11/2021 – Author: Camilla Montonati – Reviser: Irem Atabey I. Arterial blood supply 1. Internal carotid artery The arteries that supply the cerebral hemisphere and the brainstem originate from two main arteries: the first is the internal carotid artery and the second is the subclavian artery. The internal carotid artery is a branch of the common carotid artery: at the level of the superior border of the cricoid cartilage in the neck, the common carotid artery bifurcates in internal and external carotid artery. The internal one enters the carotid sheath of the fascial compartment, it continues superiorly with the internal jugular vein and the vagus, and it reaches the cranial base, at the level of the skull. The internal carotid does not realize branches until it enters the bony compartment of the skull. It takes part in the circular organization of the arterial blood. The contribution of the internal carotid artery is related to the anterior circulation, while the subclavian artery participates in the posterior circulation. 2. Subclavian artery The subclavian artery arises from the neck, it enters the foramina of the transverse process of the cervical vertebra, from the C6 to C1, then the artery moves posteriorly, it forms an angle of 90° and it converges toward the artery coming from opposite side, the contralateral artery. Successively, the subclavian artery  Pag. 2 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem enters the occipital foramen, and it gives some branches that contribute to the vascular supply of the posterior circulation. The anterior and posterior circulations have anastomoses forming the circle of Willis. 3. Internal carotid artery The internal carotid artery has cervical segments concentrated in the neck but, it is not branched in that region. Successively, the internal carotid enters the face compartment, at the level of the lateral pharyngeal spaces and from here, it goes toward the temporal bone, along its petrous portion. From the temporal bone, the course of the artery is not straight, but it is S shaped. The artery enters in the posteroinferior surface of the pyramids, and it exits at the level of the apex of these, very close to their anterosuperior surface. The petrous segment is very close to the structures inside the pyramids and the Eustachian tubes, that is the continuation of the tympanic cavity in the middle ear. Just 1 mm of bony wall separates the two structures, the artery, and the tube and so, this portion is very delicate. In the petrous segment, the internal carotid artery has not ramification and it is surrounded by sympathetic nervous plexus. The superior cervical ganglion of the sympathetic trunk has postganglionic fibers that enter the skull and cranially. Theses and the parasympathetic fibers of the cranial nerves run together, and they reach the same targets. The sympathetic plexus around the carotid, called carotid plexus, exits with the internal carotid artery near the apex of the pyramids and it reaches the middle cranial fossa. Before entering the brain, the internal carotid artery has another segment that is called cavernous, since it passes across the homonymous venous segment that has many trabeculae of connective tissue that divide the surrounding space in small cameras, forming a sort of network. The internal carotid artery passes close to the cranial nerve VI, the abducens. This last passes in the brainstem between the pons and the medulla posteriorly, it continues anterolateral through the cavernous sinus, and it reaches the superior orbital fissure passing over the internal carotid artery surrounded by the vagus nerve. In clinic, this is important due to the possibility to acquire infections arriving from the venous system that can affect both the internal carotid artery and the nerves. When the internal carotid artery is affected, it can spread the infection across the anterior circulation, and when the cranial nerve VI is infected the abduction of the eyes is compromised. The lateral wall of the cavernous sinus has other related structures (seen later). In the image can be easily seen Gasser ganglion, that is a branch of the trigeminal nerve. So internal carotid artery has this passage, but it is not branched. The last segment is the cerebral segments, that is subdivided in different tracts.  Pag. 3 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem 4. Vertebrobasilar circulation (posterior circulation) The internal cortical artery has collaterals that participate in the formation of the circle of Willis. The inferior view of the brain shows the circle of Willis, the optic chiasm, and the hypothalamus with the peduncle of the hypophysis at the center and all around this circle. The internal carotid artery contributes at the circle at the right and at the left, while the vertebral artery enters the occipital foramen posteriorly, it converges and has anastomoses to create one single trunk, that is very short but large, the basilic trunk. The basilic trunk runs along the ascending tract of the brain stem, so through the medulla and the pons. Then it gives collateral branches that participate in the circle of Willis. When the internal carotid leaves the circle of Willis, it forms the ophthalmic artery, that exists the skull through the optic canal reaching the orbits. This is the only branch that exit the skull and it is related to the optic nerve at the level of the optic canal, and it is mostly covered by dura mater. 5. Circle of Willis The basilar artery originates from the anastomosis of the two vertebral arteries, but before forming the basilar trunk, it releases some vessels that participate in the arterial supply, but they are not proper of the brain tissue. In fact, these branches contribute to the spinal cord supply, forming the anterior spinal artery. This descends and divides into collaterals vertebral arteries, that converge toward the contralateral artery, and then they supply the spinal cord on the midsagittal plane. The blood transported by these arteries, is discharged, and mixed with the one of the other vertebral arteries, that have an ascending pathway in the neck region and that have other collateral branches coming from the subclavian artery to the right and to the left. In this way, the artery contributes to the vascularization of other territories before entering the basilar trunk. At the level of the occipital foramen the basilar artery has other branches, which vascularize the cerebellum, the posterior inferior cerebellar arteries. The cerebellum has many branches coming from different collateral branches, and some originate for the vertebral artery directly. This contributes toward the posterior and the inferior aspect of the cerebellum. While, when the two vertebral arteries converge and form part of the basilar artery, they form another branch supplying the cerebellum anteroinferiorly: the anterior inferior cerebellar artery. Another cerebellar contribution originates form the ascending course of the basilic artery, this runs along the pons, and it is called the superior cerebellar artery. At the level of the pons, there are many collateral branches called pontine perforators. They are big components of the vascular system, and their occlusion has devastating consequences. Basilar artery can even form labyrinthine artery, but due to many anatomical differences their origin must be taken in brackets. The labyrinthine artery, or internal auditive artery, enters the internal auditory meatus in the labyrinth with the facial and the vestibulocochlear nerves. Anyway, the origin depends on the level of the  Pag. 4 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem vascularized region and mostly on the course of the basilar trunk. This artery can also run more anterior, and it can originate from the posterior cerebral artery, and so, it is released when circle of Willis is already formed. In general, the basilar tract involves the brain stem and cerebellum mainly, as seen before. The basilar trunk is divided in terminal branches that supply the cerebral hemisphere, such as the posterior cerebral artery. In the image can be seen an overview of the cranial base. The brain is cut and the base of the skull, the circle of Willis and its components can be seen. Moreover, it possible observing the two vertebral arteries that form the basilar trunk, the entrance of the internal auditory artery that is inside the posterosuperior surface of the pyramids at the level of the temporal bone and the cerebellar arteries. The basilar trunk divides into the posterior cerebral artery on both sides. The basilar artery has anastomoses with the internal carotid artery at the level of the pyramids, then the internal carotid artery passes the cavernous sinus and releases its branches. One of its branches is the posterior communicating artery, that communicates with the posterior cerebral artery on each side. So, the posterior communicating artery connects the internal carotid artery with the posterior cerebral artery coming from the basilar tuck. This anastomosis reaches the internal carotid artery that moves anteriorly and releases other branches. One is the middle cerebral artery that moves anteriorly, and it forms the anterior cerebral artery. The anterior cerebral artery anastomoses with its contralateral artery, forming the anterior communicating artery. Differences between the anterior and the posterior communicating arteries are that the anterior is only one and connects the anterior cerebral arteries, while the posterior communicating arteries are two and connect the internal carotid to the posterior cerebral artery, that comes from the basilar trunk. So, the communicating arteries have an unpair number. The anterior communicating artery reaches the contralateral side but, when it forms anastomoses, the anterior cerebral artery continues anteriorly. The posterior cerebral artery, coming from the basilar artery, moves from medial to lateral and, it continues posteriorly. While the middle cerebral artery continues anterior, it moves anterolateral, and it penetrates in the Sylvian fissure. The anterior cerebral artery communicates with the contralateral artery and so, it is close to midline. This last passes between the two sides of the falx and it penetrates in the fissure between the two hemispheres, it continues anteriorly parallel to the contralateral artery, very close to the floor of the anterior cranial fossa and then, it changes the direction.  Pag. 5 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem In general, this system connects the two vertebral arteries to the basilar trunk and the two internal carotid arteries to the contralateral ones. The basilar trunk is a system that allow the “backup” of blood and, it is a safe system. In fact, these vessels have variants that allow blood to vascularize the nervous tissue in case of occlusion. These variants are vessels able to change the course of the arterial supply, moving blood from the left to the right, from anterior to posterior and so on. So, brain tissue has more possibilities to have oxygen and nutrients and so, to preserve a healthy state. This is a scheme of the circle of Willis, where there are: the posterior cerebral artery, the posterior communicating artery, the internal carotid artery, the anterior cerebral artery, the anterior communicating artery, and the ones on the other side. Topographically, the anterior cerebral artery can be seen all around the hypothalamus and the optic chiasm. The orientation of the anterior cerebral artery is parallel and close to the midline. Anteriorly, it passes inside the interhemispheric fissure, it penetrates in the middle cerebral artery along the Sylvian fissure and from here, it continues more laterally and then, anterolaterally. Superficially, the posterior cerebral artery is not visible because it moves laterally, deeper, and posteriorly. These two segments have connections in between and high probabilities of aneurism are frequent in the sinuses that connect the two arteries. Moreover, the possible rapture of an aneurism allows blood to flow out of the vessels and in this way, the hemorrhage spreads throughout the supra arachnoidid space. 6. Anterior cerebral artery (3 segments A1-A3) Main Branches and territories: -anterior communicating artery à Willis’s circle -anteromedial central arteriesà caudate nucleus (internal capsule) -recurrent artery (Heubner) à internal capsule -orbitofrontal and frontopolar arteriesà olfactory cortex, medial orbital gyrus - callosal marginal artery (medial frontal, paracentral) à cingulate gyrus - pericallosal artery (terminal)à corpus callosum The anterior cerebral artery has many branches that innervate specific territories. One of these branches is the anterior communicating artery that connects two other branches and takes part in the circle of Willis. Other branches form the anteromedial arteries. They are very close to the center, and they are important for the vascularization of the basal ganglia, the caudate nucleus, and the internal capsule fibers. Another artery that drains the internal capsule is the recurrent artery.  Pag. 6 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem On the floor of the anterior cranial base, on the orbital surface of the frontal bone and posterior to the frontal lobe, the orbitofrontal (or frontobasal) artery vascularizes the inferior gyrus. This artery runs close to the prominent part of the frontal and prefrontal lobe forming the frontopolar artery. The frontopolar artery runs close to the olfactory bulb and it takes part in the vascularization of the olfactory cortex, that is part of the gyrus of the orbital portion of the frontal lobe. This artery moves anteriorly, it changes direction, and it follows the curvature of the frontal lobe moving superiorly and posteriorly. A vessel abandons the course of the anterior cerebral artery, and it ends in the prominent anterior portion of the corpus callosum. This is called callosal or pericallosal arteries and it follows the shape of the corpus callosum. This artery is very big, and it is surrounded by the curvature of the corpus callosum, it takes part in the vascularization of the cingulate gyrus, and it supply the limbic lobe. Another branch is the callosal marginal artery, that follows the curvature of the frontal lobe anteriorly, and it runs below the pericallosal artery. The callosal marginal artery is a big branch and it has some collateral branches, that form the paramedian arteries. The anterior cerebral artery cuts the hemispheres medially, and here, the paramedian arteries vascularize the median surface of the brain and the frontal lobe moving superiorly. The pericallosal artery and some branches move posteriorly, they go in the gyrus of the parietal lobe and then, they continue along the corpus callosum, the corpus striatum, the caudate nucleus and the globes pallidus and they reach the limbic lobe for the cingulate gyrus. The middle cerebral artery has different segments that move anteriorly and lately. The main branches are close to the basal ganglia, and they are posterior to the middle cerebral artery. These are the lenticulostriate arteries, they supply the lentiform and the caudate nuclei and, they have branches that can be more medial and other more lateral. In the Sylvian fissure there is the possibilities to vascularize the opercula, through the prefrontal artery, while in the central sulcus they vascularize the precentral gyrus or prerolandic gyrus. During the course of the middle cerebral artery, it has collateral branches that penetrate in the middle and the superior frontal gyrus. In the image shows the branches of the anterior cerebral artery. The two hemispheres are cut along the midline in order to look at the median surface, where the anterior cerebral artery passes. This is important for the vascularization of the median surface, for the one of the frontal lobe and the one of olfactory portion. When the artery moves superiorly, it forms the pericallosal artery that penetrate in the corpus callosum with some branches, while more posterior, some other smaller branches penetrate and take part in the vascularization of the medial surface of the gyri, that are part of the parietal lobe. 7. Middle cerebral artery (4 segments M1-M4) Main Branches and territories: - Lenticulostriate penetrating arteries (medial and lateral) à basal ganglia - Pre-Rolandic and Rolandic sulcus arteries à frontal lobe (precentral gyrus, central sulcus) - Prefrontal arteries à frontal lobe (operculum) - Temporal arteries (anterior, polar) à temporal lobe (including Wernicke’s area) - Parietal arteries à parietal lobe (supramarginal and angular gyri) - Temporo-occipital à occipital lobe (superior and inferior occipital gyri)  Pag. 7 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem They middle cerebral artery has different segments, but the main branches move anterior and lateral. They are lateral and posterior to the basal ganglia, that are mainly vascularized by the anterior cerebral artery, but even the middle cerebral artery take part in their vascularization. The lenticulostriate arteries pass inside the nuclei of the corpus striate, between the lentiform and the caudate nuclei, and some of them run more medial and some other more lateral. Successively, they move lateral, they enter the Sylvian fissure and here, they reach the opercula, that are covered by the insular lobe completely. These arteries can be subdivided depending on the vascularized operculum. A group of arteries, the prefrontal arteries, vascularize the frontal operculum, while others run more superior, they enter the Rolandic sulcus, that is the central sulcus, and they vascularize the precentral gyrus, the premotor cortex and the prerolandic motor cortex. Another group of vessels runs more posterior, it enters the parietal lobe, and it takes part in the vascularization of the gyrus of the parietal lobe. In fact, the parietal lobe is vascularized by the middle cerebral artery. In the temporal lobe, arteries enter inferiorly and posteriorly, they vascularize the region designed for earing, speaking and understand. Part of these vessels move posteriorly, they penetrate in the portion of the temporal lobe close to the occipital lobe, that includes temporooccipital participation. This is not at the level of the calcarine fissure, but it is along the superior and inferior occipital gyrus on the lateral surface. In the image, inferiorly, the medial surface of the occipital lobe is more extensively vascularized by the posterior cerebral artery, as summarized in the image. The middle cerebral artery can present aneurisms, it supplies the lateral surfaces because it entes the Sylvian fissure and it takes part in the vascularization of the superficial surface of the lobes. Only the superior part of the parietal, and the inferior part of the temporal and occipital are not innervated by the medial cerebral artery. While the artery vascularizes the opercula, the area of the central sulcus and the basal ganglia, while medial and lateral branches from the opercular drain the insular cortex. 8. Posterior cerebral artery Main branches and territories: - posterior communicating artery à Willis’ circle - medial and lateral posterior choroidal arteries à choroid plexus - anterior and posterior temporal arteries à temporal lobe - medial and lateral occipital arteries àoccipital lobe - calcarine artery à visual cortex The posterior cerebral artery forms segments. During its course, it participates in the circle of Willis after realizing the posterior communicating artery. It moves posteriorly, but it remains very close to the medial surface of the hemispheres. It divides into collateral branches that reach the choroid plexus. These arteries, the choroidal arteries, supply the lateral ventricles, and they provide medial and lateral branches. The medial group is not the most important component.  Pag. 8 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem On the medial surface of the temporal lobe, there are groups of posterior and anterior temporal arteries, that reach the calcarine fissure with many branches, and in fact it is a highly vascularized area. Most of the occipital lobe is vascularized by the posterior cerebral artery, and by the middle one just partially. The middle cerebral artery is not the main component of the lateral aspect, but it is not the same for the visual cortex. Easley the image shows the area vascularized by these arteries. The Willis ‘circle can supply an area that is affected by the occlusion of an artery or by a hemorrhage and it might avoid lesions in the nervous tissue or alteration in the circulation. 9. The meningeal vessels The mentioned vessels bring nutrients and oxygen to the brain and to the nervous system, but the meningeal sheaths are vascularized by the meningeal artery. These come from different areas, the anterior meningeal artery comes from the ethmoidal bone, the ethmoidal artery than enters the cribriform plate and it takes part in the anterior meningeal vascularization. The middle meningeal is the main one and it is part of the internal maxillary artery. This is interesting because it originates close to the mandible and to the fossa of the skull, the infratemporal fossa, and it has relationships with the splanchnocranium. It enters the skull using the foramen inside the sphenoid, the foramen spinosum and then it enters its lateral aspect. The posterior meningeal artery arises from the neck. The vessels of the external carotid artery form the ascending pharyngeal artery that uses the foramen inside the palatine fossa to move posteriorly and to enter the skull in the posterior cranial fossa.  Pag. 9 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem II. Venous blood supply 1. Sinuses of Dura Mater The venous drainage is different form the arterial supply because veins are tubes with their specific wall that surrounds the lumen. In venous drainage there are sinuses of the dura mater that have many rules and functions related to the venous system. All the sinuses are connected to each other directly or through small tracts of veins that can be impairs or paired. They form a network surrounding the brain, sinuses are in the lamination of the dura mater, forming another system that protects and envelop the brain. So, the cerebral fluid that surrounds the subarachnoid space can be controlled by the venous drainage, that has an additional hydraulic role. The CSF can reduce trauma that can be applied by the skeleton on the brain and in this way, it avoids possible lesions. Veins can have anastomosis and they can form plexi that can be found in the skull for the brain and in the splanchnocranium for the face. Sinuses of the dura mater are all inside its laminae and they create the deep system of venous drainage, that has some connections with superficial for creating anastomosis between the two systems. At the end, all the systems converge toward the internal jugular vein that is the only vein that drains the skull.  Pag. 10 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem During its course, the internal jugular vein receives additional superficial blood vessels at the level of the neck and, it enters the subclavian vein and then the anonymous vein on both side of the neck. The cerebral veins contain large amount of the blood volume, almost 70% of the total cerebral blood volume, and so, they are important in case of possible lesions. In veins, the flux is opposite, they are vessels that converge toward blood vessels with larger calibers. All the cerebral veins emerge from the nervous tissue, they enter the subarachnoid space, they pierce this space, and then they enter the lamination of dura mater draining the cranial venous sinus. As shown in the schematic image, they communicate with the superficial venous drainage, that is formed by emissary veins running across the flat bone of the squama. They form anastomosis in the tegmentum of the skull, and some branches penetrate the diploe of the flat bones. Flat bones have two cortical laminae and an inner medullary part that form the diploic structure, and these structures are drained by a group of veins, the diploic veins, that connect the internal and external venous system. This important in cases of infections, because these can penetrate the brain through the venous system that has not valves inside this organ. At base of the level of the neck, there is only one valve, formed by the internal jugular that converges toward the subclavian vein. These veins, forming the anastomosis, creates an important valve when the internal jugular veins enlarge. This valve is called inferior valve of the internal jugular vein. Since there are not valves in the venous drainage of the brain, except for the inferior valve, blood has not cleaners and since the low pressure of the flux can be inverted, infections can move and spread around easily. Fortunately, the BBB limits the diffusion of the infections. In the sinus of the dura mater, there are granulations of the arachnoidid lamina that allow the resolution of the CSF flux, and so, they are involved in the reabsorption and in the turnover of the fluid. 2. Venous drainage of the cerebral hemispheres  Pag. 11 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem The image shows the sinus of the dura mater and two sinuses along the course of the cerebral falx. One sinus runs the superior aspect of the falx, and so it is along the midsagittal plane. The other sinus is curved, posterior to the frontal sinus and it is at the level of the frontal lobe, squama, and along its inner surface. This sinus follows the cortex and continues posteriorly, until it arrives at the confluence of the sinuses, that is where this sinus converges toward the other sinuses. Another sinus, called inferior sagittal sinus, is smaller than the previous one, it follows the cerebral falx on its inferior aspect, and it is parallel to the other. This one looks like the previous one, but it is smaller, and it is more inferior. The inferior sagittal sinus does not reach the confluence of the sinus, because, where the falx meets the tentorium cerebelli, it converges toward the inferior sagittal sinus and it forms another sinus, the straight sinus, through the great cerebral vein. The straight sinus moves toward the confluence of the sinuses, that is at the level of the occipital prominence/protuberance on its the internal surface. In the image are shoed paired sinuses that arrive at the level of the straight sinus.  Pag. 12 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem Another image shows the large sinuses that arrive at the confluence, the transverse sinus, the posterior sinus in the posterior cranial fossa and the transverse sinus that receives venous blood form the sinus of the petrous bone, the petrous sinus. Other veins come from plexi that are at the level of the basilar portion of the occipital lobe and at the level of the occipital protuberance, where there is the confluence of the sinuses. There are other paired sinuses, the occipital sinus that can be seen in the images. As shown in the image, the vertebral artery is surrounded by a plexus that is big and that converges toward the cavernous sinus. This is more anterior, and it runs along the sphenoid on both sides, where the body of this bone continues with the greater wings, close to the Meckel cave, where there is the Gasser’s ganglion. 3. Cavernous sinus The cavernous sinus receives fibers from this plexus, from the pterygoid venous plexus, vessels from the orbits and from the ophthalmic vein. Superiorly and inferiorly, the cavernous sinus drains blood from different vessels, and this is a possible region of infections in the splanchnocranium.  Pag. 13 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem In the superior view there is the transversus sinus that moves from medial to lateral, it arrives at the confluence of the sinuses, and in the image, it is the mirror image of the other side. Anyways, there are many terminal branches, and one size is usually more represented than the other and so usually there are some variants. At the level of the confluence of the sinus there is the occipital sinus, that is made by two sinus that usually converge in the circle of Willis. These move form medial to lateral until they arrive at the confluence of the sinuses, where the transverse sinus collects the vessels that come from the sagittal sinus superiorly and form the straight sinus inferiorly. The straight sinus divides the vessels into two sides that enter in the jugular vein. Therefore, from the confluence of the sinuses all the vessels coming from the superior aspect of the midsagittal plane divide into two sides and then, they move form posterior to anterior and from medial to lateral. The internal jugular vein is medial and so, these vessels form a curvature, acquiring an S -shaped part that forms the sigmoid sinus. This continues and enters in the interna jugular vein, where there is the arrival of the blood coming from the anterior portion. In the anterior portion there is petrous sinus that is in relation with the petrous portion of the temporal bone, the superior petrous sinus that is along the superior angle that divides the anterosuperior and the posterosuperior aspect of the pyramids and inferior petrosal sinus that is between the pyramids and the occipital bone. This last often projects directly in the internal jugular vein, while the superior one enters in the sigmoid sinus posterolaterally. The two petrosal sinuses are drained by blood vessels that surrounds the hypophysial region so, there are oriented along the circle of Willis. All around the hypothalamus and the hypophysis, there is the corona made of venous blood, that is formed by the right and left cavernous sinuses on both sides of the hypothalamic region. This has connection with the anterior and the posterior system through the intercavernous sinuses. They are two sinuses because each cavernous sinus converges medially and delaminates in order to surround the hypophysial and the hypothalamic peduncles. At the level of the posterior communication, there is the basilar plexus that is along the clivus of the occipital bone. The basilar plexus descends the body of the sphenoid along the occipital bone, and it surrounds the area of the hypothalamus posteriorly. While, on both side the two cavernous receive blood from another sinus that is located along the superior orbital fissure. This sinus, the sphenoparietal sinus lies along the posterior margin of the lesser wings of the sphenoid, in between the anterior and the middle cranial fossa, and receives from the lateral aspect of the two hemispheres.  Pag. 14 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem The convergence of the veins comes from the meningeal sheaths and the most important is the middle meningeal artery that converges toward the cavernous sinus. This last receives veins coming from the orbits, the superior ophthalmic veins, that drain the ocular globe, the superior eyelids and part of the frontal cutaneous layer and vessels coming from the orbits that do not drain them. These last come from the infratemporal and then they enter in the inferior orbital fissure and in the pterygopalatine fossa. In this way infections from the teeth and the maxillary area can spread across the brain passing form the inferior ophthalmic veins, continuing through the inferior fissure, and entering the cavernous sinuses. In general, it is possible all these systems can be extrapolated thanks to the communication between the sinuses and the veins inside the skull. The scheme shows the transverse sinus, it is sigmoid shaped, it does not move anteriorly and medially only, but it descends and converges toward the bulb of the internal jugular vein reaching the neck. This is another view of the cavernous sinus that shows the relationships with the cranial nerves. It possible to see the petrous portion of the cavernous sinus and the posterior and anterior intracavernous portion all around the peduncles of the hypophysis. The internal carotid artery exits the skull, and the ophthalmic artery enters in the optic canal with the optic nerve. The ophthalmic artery enters in the superior orbital fissure passing with the oculomotor, the abducens and the cochlear nerves, through it. They are very close to the internal carotid artery, the abducent arrives dorsally, while the trigeminus has the ophthalmic branch that runs along the lateral wall of the cavernous sinus, while the other two have completely different orientations. This image shows the basilar plexus, the vagus, and the vertebral plexus. The transverse sinus converges toward the sigmoid sinus, that enters the internal jugular vein. This passes close to the glossopharyngeal, vagus and accessory nerves and then it enters the foramen lacerum or jugular foramen posteriorly.  Pag. 15 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem A schematic view of this organization: Some vessels surround the hypophysis that is closed by fat coming from the myelinization of the dura mater. These vessels have relationships with the nerves that are close to the internal carotid artery, such as the abducens on the lateral wall and anteriorly the oculomotor, the trochlea, the ophthalmic and the branches of the trigeminal nerves, that are the maxillary and the mandibular nerve. This last abandons immediately the course penetrating the oval foramen inferiorly. 4. Anastomosis intra-extracranial veins This is an overview of the face that shows the superficial and the deep venous systems, their connection, and the venous drainage. Veins arrive form the cavernous sinus in the superior orbital fissure, but inferiorly vessels arrive from the area between the pterygoid muscles. For this reason, infections can spread very far away from veins. It is possible to see anastomoses made by the facial veins, that are between the inner commissure of the eyes and the other vessels of the eyes, between the vessels of the nose, the one of the cheeks and the one of the lips, they both reach the cavernous sinus. These vessels can cause the inversion of the flux and as before, they can spread very dangerous infections. Moreover, the inversion of the flux is possible since cerebral veins have not any muscles that reach the nervous tissue and since the pressure is very low allowing the inversion and the dissemination of bacteria and virus into the nervous system.  Pag. 16 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem The mentioned plexus is the pterygoid venous plexus, that is an extensive valveless plexus of veins that parallels the medial two thirds of the maxillary artery on the lateral aspect of the medial pterygoid muscle, within the infratemporal fossa. The view shows the superior cerebral vein that converges toward the superior and the inferior sagittal sinus, it forms the middle cerebral vein that enters the sphenoparietal sinus, the cavernous sinus, the superior and petrous sinus. Some of its vessels enter the transverse sinus, the sigmoid sinus and at the end the internal carotid. This is an area of convergences. 5. Cerebral venous sinus thrombosis (CVST) In cases of trauma and lesions that affect the vascularization of the brain, arterial and venous implication has different effects and damages. The thrombosis is less prevalent than arterial stroke and it affects adult and children mostly, while the arterial stroke affects older people. Moreover, the thrombosis affects more woman than men, its etiology is mainly related to the genetic and so, it can be inherited. This pathology can be linked to thrombophilia, other blood disorders, dehydration and idiopathy. In cases of older people, thrombosis associated to the sclerosis. The deficit is usually focal and in this case the obstruction affects small single points, but in other cases it can be more generalized. In these cases, the pressure of the CSF increases, blocking the venous sinuses and impeding the flux of the liquor.  Pag. 17 a 17 International Medical School – NEUROAN #14 – prof. Dellavia – Vascular supply to the cerebral hemispheres and brainstem