CNS - Vascular Supply PDF

CNS – Vascular Supply CNS – Arterial Blood Supply Human Brain: • Weight constitutes app. 2-2.5% of body weight • Receives app. 15% (1/6th) of cardiac output → app. 750 ml blood/min • Utilizes app. 20-25% (1/5th) of oxygen of total body → High metabolic rate Sources of Arterial Blood Supply to Br...

CNS – Vascular Supply CNS – Arterial Blood Supply Human Brain: • Weight constitutes app. 2-2.5% of body weight • Receives app. 15% (1/6th) of cardiac output → app. 750 ml blood/min • Utilizes app. 20-25% (1/5th) of oxygen of total body → High metabolic rate Sources of Arterial Blood Supply to Brain • Internal Carotid a. • Vertebral a. Sources of Arterial Blood Supply to Brain • 2 pairs of arteries • Interconnected in cranial cavity • In subarachnoid space • Form cerebral arterial circle (an anastomosis) on inf surface of brain around the infundibulum of the hypophysis Circle of Willis Sources of Arterial Blood Supply to Brain Internal Carotid Arteries Supply: • Same side • Part of brain hemispheres • Eye & accessory structures • Front of forhead • Part of nasal cavity Sources of Arterial Blood Supply to Brain Internal Carotid Artery • Origin: Bifurcation of common carotid a. • Bifurcation: Upper level of thyroid cartilage, C4 • Carotid sinus – baroreceptors at its bifurcation • Is a “terminal branch” of common carotid a. • No branches in neck • Described in parts named according to area it passes • Enters skull thru carotid canal: Sources of Arterial Blood Supply to Brain Internal Carotid Artery - Parts • Cervical: Part in neck. No branches • Petrous: Part inside canal which is in petrous part of temporal bone • Cavernous: Part inside cavernous sinus Pierces dura mater & enters subarachnoid space • Cerebral: When it reaches ant. perforated substance it divides into its terminal branches: Ant. cerebral a. & middle cerebral a. Sources of Arterial Blood Supply to Brain Internal Carotid Artery • Enters skull thru carotid canal: • • • • Ext. opening on inf. surface of temporal bone External opening post. to foramen spinosum & medial to styloid process Canal makes an S shaped curve Carotid plexus of nerves (sympathetics) also pass thru canal Sources of Arterial Blood Supply to Brain Internal Carotid Artery • Part in carotid canal: Petrous part • Passes in close relation to cavernous sinus Cavernous part • Passes thru dura, enters subarachnoid space Sources of Arterial Blood Supply to Brain Internal Carotid Artery – Petrous Part • Part in carotid canal • Carotidotympanic a: Goes to middle ear • Pterygoid a. (a.k.a. Vidian a.): Small branch Sources of Arterial Blood Supply to Brain Internal Carotid Artery – Cavernous Part • Cavernous sinus branches: Multiple small branches • Inf hypophysial a. : To hypophysis • Trigeminal ganglion branch: Small/thin • Ant. meningeal branch: Supplies meninges of ant. cranial fossa Sources of Arterial Blood Supply to Brain Internal Carotid Artery – Intracranial Branches: • Ophthalmic a. • Anterior communicating a. • Middle cerebral a.: Within lateral sulcus • Anterior cerebral a.: Within longitudinal fissue, both travel parallel to each other • Posterior communicating a. • Ant choroideal a. Sources of Arterial Blood Supply to Brain Vertebral Arteries Supply: • Brain stem • Cerebellum • Occipital lobe • Part of thalamus • Rest of brain tissue supplied by int carotid arteries Cerebral Circulation Vertebral Arteries • Origin: 1st part of each subclavian a. – lower neck • Course: Prevertebral Vertebral – passes superiorly thru transverse foramina of C6 – C1 Atlantic Intracranial – passes thru foramen magnum to enter cranial cavity → gives off small meningeal branch Cerebral Circulation Vertebral Artery • Intracranial part – passes thru foramen magnum, enters cranial cavity • Continues up ventral surface of medulla • At caudal border of pons, R & L parts join to form basilar a. Cerebral Circulation Vertebral Artery – Branches (include) Anterior spinal a. • Single, formed by union w/companion side. • Descends in ant median fissure of spinal cord • Supplies Ventro-lateral 2/3rds of cervical spinal cord Ventro-medial part of medulla Posterior spinal a. • Supplies Dorsal 1/3rd of spinal cord Post inferior cerebellar a. (PICA) • Largest branch • Supplies Cerebellum Dorsolateral part of medulla Cerebral Circulation Vertebral Artery ➔ Basilar Artery • Formed by the joining of the 2 vertebral arteries at pontomedullary junction • Ascends along ventral midline of pons • Terminates near rostral border of pons by dividing into 2 → Post. cerebral a.a. Cerebral Circulation Branches of Basilar Artery (include) • Ant. Inf. cerebellar a.a. (AICA) Supplies inf. surface cerebellum • Pontine a.a. Supplies pons • Labyrinthine a.a. Follows course of CN VIII Supplies inner ear • Sup. cerebellar a.a. Supplies Superior cerebellum & part of rostral pons Sources of Arterial Blood Supply to Brain Basilar Artery ➔ Posterior Cerebral Artery (PCA) • At rostral end of midbrain, basilar a. bifurcates into a pair of posterior cerebral arteries → terminal branch of basilar a. • Supplies Occipital lobe Cerebral Circulation Cerebral Arterial Circle – Circle of Willis • Interconnecting basilar & internal carotid systems of vessels • Formed in interpeduncular fossa, around infundibulum & optic chiasm • Ensures blood brought by int. carotid a.a. & basilar a. is distributed with equal pressure Basilar a. Cerebral Circulation Cerebral Arterial Circle – Circle of Willis • 1 ant. communicating a. connecting R & L ant. cerebral aa. to each other AND • 2 post. communicating a.a. (1 on each side), connecting int. carotid a. w/ post. cerebral a. • Middle cerebral a. Branches of Int Carotid a. Ophthalmic a. Posterior communicating a. Middle cerebral a. Anterior cerebral a. Cerebral Circulation Medial Surface of Brain Cerebral Circulation Circle of Willis - Importance • Equalizes blood flow to various parts of brain • Maintains constant supply of O2 & glucose even when a contributing a is narrowed or in head movements • Provides collateral circulation in case of occlusion of 1 or more contributing a.a. MR Angiogram Cerebral Circulation Normal Brain Angiogram Cerebral Circulation Clinical Correlate: Cerebrovascular Accidents & Brain Stem Lesions • Stroke ak.a. cerebrovascular accident (CVA): • Interruption of blood flow to brain or brainstem resulting in impaired neurological function lasting more than 24 hours • Transient ischemic attack (TIA) or mini-stroke: Neurological impairment resolving within 24 hours • Types of stroke • Ischemic stroke • Hemorrhagic stroke • Uncommon to injure a part of brain stem w/o involving any of the cranial nerves • The cranial nerve signs (defects) will localize the injury Unenhanced CT scan: hemorrhagic conversion of ischemic stroke app 72 hours after symptom onset Cerebral Circulation Clinical Correlate: Aneurysm • Abnormal balloon-like swelling of an artery • May rupture → Blood enters subarachnoid space → Subarachnoid hemorrhage →Blood enters into brain → Intracerebral hemorrhage • 90% of cerebral aneursysms occur in Circle of Willis Contributing Factors (Exact mechanism unknown), • Congenital (genetic) predisposition – tunica media defects (*) • Hypertension • Cigarette smoking • Injury or trauma to blood vessels • Complication from some types of infections Ophthalmic a. – Int Carotid aneursym Cerebral Veins • Either lacks muscular layer or very thin walled • No valves • After draining cerebral tissue (parenchyme), they travel in subarachnoid space → pierce arachnoid mater & int layer of dura mater & open into dural venous sinuses • Can be divided into superficial and deep groups • Arranged around the gyri and sulci of the brain Cerebral Veins – Superficial System • Responsible for draining cerebral cortex • Superior cerebral veins: Drain the surface → superior sagittal sinus. • Superficial middle cerebral vein: Drains lateral surface of each hemisphere → cavernous or sphenopalatine sinuses • Inferior cerebral veins: Drain inf. aspect of each cerebral hemisphere → cavernous & transverse sinuses • Superior anastamotic vein (Trolard): Connects the superficial middle cerebral vein to the superior sagittal sinus • Inferior anastamotic vein (Labbé): Connects the superficial middle cerebral vein to the transverse sinus Cerebral Veins Cerebral Veins – Deep System • Subependymal veins: Numerous subependymal veins. Receive blood from the medullary veins → dural venous sinuses • Great cerebral vein (vein of Galen): Formed by union of 2 deep veins : internal cerebral v.v. under corpus callosum → straight sinus • Medullary veins: Originate 1-2cm below cortical grey matter → subependymal veins Drain the deep areas of the brain Cerebral Veins – Deep System Deep Veins of the Brain