Blood supply to the brain The arterial supply to the brain can be divided into arteries responsible for anterior circulation and arteries responsible for posterior circulation - Arteries carrying out anterior circulation arise from the INTERNAL CAROTID ARTERIES. Arteries carrying out posterior circulation arise from the VERTEBRAL ARTERIES. Anterior circulation: - Starts with the internal carotid artery. Internal carotid arteries arise in the neck from the common carotid arteries. They travel superiorly and enter the cranial cavity through the carotid canals in the temporal bones. The internal carotid artery then gives three branches: 1. anterior cerebral artery 2. middle cerebral artery 3. posterior communicating artery Anterior cerebral artery: - - Arises from the internal carotid artery at the anterior perforated substance, it then passes anteriorly above the optic chiasma into the medial longitudinal fissure. it contributes towards the circle of Willis which is an interconnected ring of arteries at the base of the brain. It also provides multiple pathways for oxygenated blood to supply the brain if any of the arteries are constricted. It supplies the metal surface of the cerebrum above the corpus callosum and the orbital part of frontal lobe. Branches of anterior cerebral artery: - - Anterior communicating artery which is very short and connects the right and left anterior cerebral arteries therefore closing the circle of Willis anteriorly. Medial frontal basil artery which Supplies the orbital part of the frontal lobe. Polar frontal artery which runs on the medial surface of the cerebral hemisphere and goes to the frontal pole of the frontal lobe. Pericallosal archery which is a continuation of the anterior cerebral artery and gives off branches supplying the corpus callosum and precuneal branches supplying the inferior part of the precuneus. Callosomarginal artery which is the median artery of the corpus callosum and runs parallel to the pericallosal artery in the cingulate sulcus. This supplies the frontal lobe, anterior parietal lobe and the paracentral area. Cingular branches which arise from the callosomarginal artery which are the terminal branches of this artery and it also gives rise to the paracentral artery which goes to the paracentral area and supplies the superior parts of the precentral gyrus and post central gyrus. Middle cerebral artery: -This is the second largest and most direct branch of the internal carotid artery and it supplies the insula cortex. Branches of the middle cerebral artery: - Superior terminal branch Inferior terminal branch Branches of the superior terminal branch: - The lateral frontal basal artery arises from it and this supplies the frontal lobe, inferior frontal gyrus and the medial frontal gyrus. The artery of the precentral sulcus (pre Rolandic artery) courses over the cortex supplying the precentral sulcus on either side. The artery of the central sulcus supplies the area of the central sulcus aka Rolandic artery. Branches of the inferior terminal branch: - The anterior temporal artery, which courses out of the lateral sulcus supplying the anterior 1/3 of the inferior, middle and superior temporal gyri. The middle temporal artery supplies the temporal lobe. The posterior temporal artery supplies the lateral surface of the posterior temporal lobe. A branch of the middle cerebral artery to the angular gyrus also arises from the inferior terminal branch. The anterior parietal artery, which supplies the anterior part of the parietal lobe. The posterior parietal artery, which supplies the posterior part of the parietal lobe. The frontal branches, which supply the posterior part of the frontal lobe. Posterior communicating artery: - Rises from the internal carotid artery Forms part of the circle of Willis Supplies the: thalamus, posterior parts of optic tract, optic chiasma, mammillary bodies and hypothalamus. Posterior circulation: - The vertebral branches give rise to the branches responsible for the posterior circulation of the brain. The vertebral arteries merge to form the basilar artery and the basilar artery divides to form the two posterior arteries. Posterior cerebral artery: - Supplies the cerebral peduncle, optic tract, occipital lobe, inferomedial surface of the temporal lobes and the right posterior cerebral artery which sends perforating branches to the thalamus. Branches of the posterior cerebral artery: - Medial occipital artery and its branches which supply the corpus callosum, medial occipital lobe and medial parietal lobe. The dorsal branches of the corpus callosum also arise from the medial occipital artery and supplies the dorsum of the corpus callosum. The parietooccipital branch supplies the medial surface of the occipital lobe and parieto-occipital sulcus. Venous Drainage of the brain Cerebral veins 1. 2. - The veins of the brain are thin-walled and valve-less. There are two types of venous systems within the cerebral veins: Superficial venous system – which primarily drains the grey matter of the brain. Deep venous system- which drains the deep structures of the brain and the white matter of the cerebral hemisphere. Both sets of veins drain into the internal jugular vein. Superficial veins of the brain: - Drain the grey and superficial most white matter of the cerebral cortex. It is found on the surface of the cerebrum in the subarachnoid space between the arachnoid mater and pia mater. The veins form an anastomotic network with each other and the deep cerebral veins. Blood from the superficial veins are drained to the sinuses in the brain in the following manner: 1. The frontal and parietal lobes drain into the superior sagittal sinus. 2. The temporal and occipital lobes drain into the right and left transverse sinuses. - The deep cerebral veins drain into the straight sinus or transverse sinus. Pathway of the superior cerebral veins: - - Unlike most veins, the superficial veins do not follow the arteries. Their path takes them across the subarachnoid space where they pierce the arachnoid mater, cross the subdural space, and then pierce the meningeal layer of the dura mater to finally drain into the dural venous sinuses. The subarachnoid space, arachnoid mater, subdural space and dura mater all drain into the superior sagittal sinus. Blood then empties into the sigmoid sinus which is continuous with the internal jugular veins inferiorly. There are five veins: 1. 2. 3. 4. 5. Superior cerebral veins Superior middle cerebral vein (of Sylvius) Superior anastomotic vein (of Trolard) Inferior anastomotic vein (of Labbe) Inferior cerebral veins Superior cerebral veins - They are a network of veins within the subarachnoid space - They drain the anterior, superolateral and medial surface of the frontal lobes. They also drain the anterior, superolateral and medial surface of the parietal lobes. They drain the superolateral medial and posterior surface of the occipital lobes. The superior cerebral veins drain into the superior sagittal sinus. The superficial middle cerebral vein of Sylvius: - This is a single vein present laterally in both sides of the brain in the subarachnoid space. It descends anteriorly along the lateral sulcus and then arches medially along the sphenoid ridge. It drains the lateral surfaces of the frontal, parietal and temporal lobes. The vein continues from the sphenoid ridge to drain into the cavernous sinus. Superior anastomotic vein of Trolard: - This is a single vein present laterally in both sides of the cortex in the subarachnoid space. This vein connects the superior middles cerebral vein to the superior sagittal sinus by arching over the superior lateral surface of parietal lobe. It drains the superolateral parietal cortex and drains into the superficial middle cerebral vein and superior sagittal sinus. Inferior anastomotic vein of Labbe: - They are also present bilaterally in the subarachnoid space. This vein is not present in everyone, and its exact position varies. It connects the superior middle cerebral vein with the transverse sinus. It drains the lateral aspects of the temporal lobes and subsequently drains into the superior middle cerebral vein and transverse sinus. Inferior cerebral veins: - 1. 2. 3. 4. 5. - They have a close relationship with the deep venous structures It courses over and drains the inferolateral surfaces of the temporal lobe and the orbital surfaces of the frontal lobe. It drains to the closest deep venous sinuses or deep venous veins. There are five sinuses which receive drainage from the inferior cerebral veins and includes the following: Transverse sinuses Superior petrosal sinuses Cavernous sinus Sphenoparietal sinuses Inferior sagittal sinus The inferior cerebral veins drain into deep veins such as the: basal vein, (there is one basal vein for each hemisphere and travels posteriorly around the mid brain) and the inferior cerebral veins on the inferolateral surfaces of the temporal lobes which drain to the closest deep venous structure. Deep cerebral veins: - Internal structures that are drained by the deep veins and tributaries include the thalamus, hypothalamus, corpus callosum, septum pellucidum, choroid plexuses and the white matter of the cerebral hemisphere. Internal cerebral veins: - They begin at the interventricular foramen (of Munro) and runs backwards in the tela choroidea in the roof of the third ventricle. The two internal cerebral veins merge forming the great cerebral vein. One of its major tributaries is the thalamostriate vein which lies on the floor of the lateral ventricle and returns blood form the caudate nucleus and thalamus. The corpus striatum (which is the input unit of the basal ganglia) and internal capsule are drained by the superior and inferior striate veins which drain into the internal cerebral vein and basal vein respectively. Great cerebral vein: - They are formed by the union of the two internal cerebral veins and passes posteriorly beneath the splenium of the corpus callosum to the straight sinus Blood from the basal veins, occipital lobes and corpus callosum also drain into them. Basal veins: - There are two present and they travel around the midbrain to the great cerebral vein The basal vein is formed by the union of the anterior cerebral vein, deep middle cerebral vein and some of the inferior striate veins and begins near the anterior perforated substance.
