Lecture 8_ The Anatomy of the CNS Vasculature.pdf

The Anatomy of the CNS Vasculature Dr. Kelly C. S. Roballo [email protected] VCOM-Main Building Room 341 Learning Objectives 1) 2) Identify all major arterial and venous vessels on the external surface of the cerebrum, brain stem, and spinal cord. Describe the Circle of Willis, its surroundin...

The Anatomy of the CNS Vasculature Dr. Kelly C. S. Roballo [email protected] VCOM-Main Building Room 341 Learning Objectives 1) 2) Identify all major arterial and venous vessels on the external surface of the cerebrum, brain stem, and spinal cord. Describe the Circle of Willis, its surrounding structures, and the clinical significance of this vascular structure, especially if certain communicating arteries are not present. 3) Describe neurological deficits related to common vascular lesions in the cerebrum, brain stem, and spinal cord. 4) 5) Identify the important intraparenchymal arteries that supply the CNS structures. Describe the directions of venous blood flow out of the cerebrum, brain stem, and spinal cord, and identify specific dural sinuses of the skull and brain Blood Supply to the Brain: Internal Carotid Artery and Vertebral Artery Vertebral Artery Internal Carotid Artery (70% of blood supply) Four named divisions of internal carotid artery: 1. cervical – located in the lateral pharyngeal space 2. petrous – petrous portion of temporal bone 1) Internal carotid arteries—enters the cranial cavity 3. cavernous – S-shaped in the cavernous sinus through the base of the skull. 4. Cerebral – located in the chiasmatic cistern 2) Vertebral arteries—enters the cranial cavity through the of the subarachnoid space foramen magnum. These arteries traverse the neck by passing through foramina transversarium of cervical vertebrae. The Vertebrobasilar System and the Circle of Willis The circle of Willis joins the major vessels that supply the right and left sides of the brain. The circle includes the major vessels to the cerebral hemispheres: the anterior, middle, and posterior cerebral arteries. The circle is completed by anterior and posterior communicating arteries. Arterial Supply to the Brain: Internal Carotid and Vertebral Arteries Internal Carotid artery Vertebral artery The diagram on the left shows the left common and internal carotid arteries and the left vertebral artery. The MRI angiograph on the middle is an anterior view showing both the right and left common and internal carotid arteries and right and left vertebral arteries. The image was taken following introduction of contrast material into the arterial system. Arteries at the Base of the Brain On the anterior surface of the brainstem the vertebral arteries join to form the basilar artery. The vertebral and basilar arteries supply branches to the brainstem and cerebellum. The basilar artery terminates when it divides into the right and left posterior cerebral arteries. The internal carotid artery branches into anterior and middle cerebral arteries. The Middle Cerebral Artery The middle cerebral artery supplies the lateral surface of each cerebral hemisphere. It emerges from the lateral sulcus and radiates over the hemisphere. The lateral sulcus is spread apart in the picture on the right. The Anterior and Posterior Cerebral Arteries The internal carotid artery branches into anterior and middle cerebral arteries Branches of the anterior and posterior cerebral arteries are prominent on the basal and medial surfaces of each cerebral hemisphere. Distribution of the Cerebral Arteries Lateral view of the left cerebral hemisphere. Distribution of the Cerebral Arteries Medial surface of the right cerebral hemisphere. Coronal Section Coronal Section Transverse Section Functional Centers on the Surface of the Cerebrum Left lateral view of the telencephalon Regions supplied by branches of the middle cerebral a. (MCA) are shaded green. Medial view of right cerebral hemisphere Regions supplied by the anterior cerebral a. (ACA) are shaded red; regions supplied by the branches of the posterior cerebral a. (PCA) are shaded blue. Certain disorders or deficits are indicative of arterial occlusion in a certain territory. A failure, deficit, or outage of the speech center suggests an occlusion of the MCA., hemianopsia suggests an occlusion of the PCS, and paralysis and sensory disturbances in the lower limbs suggest an occlusion of the ACA. *Clinical Correlation Distribution of the Cerebellar and Brainstem Arteries The cerebellum is supplied by 3 main branches derived from the vertebral and basilar arteries: 1. Superior cerebellar artery 2. Anterior inferior cerebellar artery 3. Posterior inferior cerebellar artery The brainstem is supplied by adjacent arteries: 1. Vertebral arteries and branches 2. Anterior spinal artery 3. Basilar artery – pontine arteries 4. Posterior inferior cerebellar artery Distribution of the Cerebellar and Brainstem Arteries AICA The cerebellum is supplied by 3 main branches derived from the vertebral and basilar arteries: 1. Superior cerebellar artery 2. Anterior inferior cerebellar artery 3. Posterior inferior cerebellar artery PICA (occlusion = loss of pain and temperature sensation to the ipsilateral face and contralateral body The brainstem is supplied by adjacent arteries: 1. Vertebral artery 2. Anterior spinal artery 3. Basilar artery 4. Posterior inferior cerebellar artery Blood Supply to the Spinal Cord Posterior intercostal arteries arise from the thoracic aorta. A posterior branch from the posterior intercostal arteries gives off a spinal branch. The spinal branch gives off anterior and posterior radicular arteries. These supply arterial blood to the anterior and posterior nerve roots. At a limited number of segments, the spinal branch will also give rise to a segmental medullary artery. These will connect with the anterior or posterior spinal artery and “reinforce” the arterial supply. Blood Supply to the Spinal Cord The vertebral artery, within the cranial cavity, gives rise to left and right anterior and posterior spinal arteries. The left and right anterior spinal arteries join to form an anterior spinal artery in the midline of the spinal cord. The anterior and the left and right posterior spinal arteries are “reinforced” by branches derived from posterior intercostal arteries. The blood supply to the spinal cord is considered to have two components: 1. Vertical—anterior and posterior spinal arteries 2. Horizontal—segmental arteries that originate from posterior intercostal arteries Not all posterior intercostal arteries contribute equally to the spinal arteries. In the lumbar region, one of the posterior intercostal arteries gives off a large branch, the Great anterior segmental medullary artery (of Adamkiewicz) Dural Sinuses Venous Drainage of the Brain The superficial veins drain blood from the cerebral cortex (via cortical veins) and white matter (via medullary veins) directly into the dural sinuses. The deep veins drain blood from the deeper portions of the white matter, basal nuclei, corpus callosum, and diencephalon into the great cerebral vein, which enters the straight sinus. The two venous regions (those of the superficial and deep veins) are interconnected by numerous intracerebral anastomoses Accessory drainage pathways of the dural sinuses The dural sinuses have many accessory drainage pathways. These anastomoses are of clinical interest because their normal direction of blood flow may reverse (no venous valves), allowing blood from extracranial veins to reflux into the dural sinuses. This mechanism may give rise to sinus infections that lead, in turn, to vascular occlusion (venous sinus thrombosis). The most important accessory drainage vessels include the following: • Emissary veins (diploic and superior scalp veins), • Superior ophthalmic vein (angular and facial veins) • Venous plexus of foramen ovale (pterygoid plexus, retromandibular vein) • Marginal sinus and basilar plexus (internal and external vertebral venous plexus) Venous Drainage of the Brain The internal jugular vein provides the main route of venous drainage from the brain. There are numerous smaller accessory drainage pathways. Though a vertebral vein runs along with the vertebral artery in the transverse foraminae, the vein provides only an accessory route of drainage for the brain. Venous Drainage of the Spinal Cord The internal and external venous plexus connect veins in the lumbar region (and pelvis) to veins in the brain. These veins can be the route for malignant cells to metastasize from the pelvis (in the case of prostate cancer) to the brain. Extracerebral Hemorrhages Extracerebral hemorrhages are defined as bleeding between the calvaria and brain. Because the bony calvaria is immobile, the developing hematoma exerts pressure on the soft brain. Depending on the source of the hemorrhage (arterial or venous), this may produce a rapidly or slowly developing incompressible mass with a rise of intracranial pressure that may damage not only the brain tissue at the bleeding site but also in more remote brain areas. Three types of intracranial hemorrhage can be distinguished based on their relationship to the dura mater: a) Epidural b) Subdural c) Subarachnoid hemorrhage *Clinical Correlation Berry Aneurysms and Intracerebral Hemorrhages Berry aneurysms occur in vessels at the base of the brain. Rupture of berry aneurysms is the most frequent cause of subarachnoid hemorrhage. *Clinical Correlation Intracerebral hemorrhage involves the rupture of a vessel within the brain parenchyma. In this example, a vessel supplying the basal ganglia has ruptured. Aneurysm • An aneurysm is a ballooning at a weak spot in an artery wall • Almost never causes symptoms unless it ruptures • A ruptured aneurysm can result in internal bleeding, stroke, and can sometimes be fatal. *Clinical correlation Cerebrovascular Disease and Ischemic Stroke Cerebrovascular disease is an important source of blood flow disturbances to the brain. Such disturbances may interfere with the delivery of blood and result in ischemia. Ischemia will result in hypoxia, which describes a lack of oxygen. Learn these terms: • Ischemia—local anemia due to mechanical obstruction • Hypoxia – less than normal amounts of oxygen • Emboli – any plug that blocks a blood vessel • Thrombus – a plug formed of blood elements Stroke • Blood supply to part of your brain is interrupted or reduced The most common type (80%) (thrombotic, embolic) Cholesterol deposits Oxygen is the most vital supply (energy) to the brain *Clinical correlation