Blood Supply. Allen Chung, class of 2013

Transcription

1 Blood Supply Allen Chung, class of 2013

2 Objectives Understand the importance of the cerebral circulation. Understand stroke and the types of vascular problems that cause it. Understand ischemic penumbra and regulation of cerebral blood flow. Describe the origin and distribution of the blood supply to the cerebral hemispheres including the internal carotid, anterior cerebral, middle cerebral, posterior cerebral, and anterior choroidal arteries and the territories they supply. Be able to identify anterior, middle, and posterior cerebral arteries in lateral and anterior-posterior view angiograms. Describe the vessels associated with the Circle of Willis. Describe the origin and distribution of the blood supply to the brainstem including the territories supplied as shown in cross sections of brainstem. Be able to draw the diagram of blood vessels (vertebral and carotid supply to the Circle of Willis) on a figure of the brainstem. Describe the origin and distribution of the blood supply to the spinal cord. Describe the venous drainage for the hemispheres.

3 Why is Blood Supply Important Brain is very active metabolically Brain is 2% of body weight Uses 15% of cardiac output Consumes 20% of total available O 2 cerebral blood flow 750 ml/min cerebral blood volume 100 ml circulating blood turns over 7x/min Chris Cohan, Ph.D. Dept. of Pathology University at Buffalo

4 Why is Blood Supply Important Brain deprived of blood for 20 sec unconsciousness 4-5 min coma, irreversible unconsciousness or death Some areas are more vulnerable to oxygen loss than others, eg Basal Ganglia, Hippocampus, Frontal Lobes

5 Why is Blood Supply Important Stroke is the most common neurological disorder! 795,000 strokes each year in US 140,000 deaths/yr from stroke 3rd leading cause of death in US Stroke is the leading cause of serious, long-term disability

6 Why is Blood Supply Important Consequences of lost blood supply are severe- loss of sensory, motor, and cognitive function. Increase in aging population, obesity, diabetes suggests cerebrovascular disease will continue to be a major problem.

7 Why is Blood Supply Important Blood vessels supply specific territories throughout the CNS. The pathway structures in these territories produce characteristic cluster of symptoms when blood supply is impaired. Knowledge of these pathways and territories is essential for understanding localization, interventions, and prognosis.

8 Examples of Territories Infarct of MCA Ant Spinal Infarct Clustering of symptoms Infarcts cause focal deficits based on territories supplied by blood vessels

9 Stroke Stroke a syndrome caused by disruption of brain circulation; characterized by sudden onset of neurological deficits lasting >24 hrs involving focal symptoms that correlate with a brain area supplied by the affected vessel.

10 A. Ischemia 67% Causes of Stroke TIA- transient ischemic attack Infarction 1. Thrombosis 2. Embolus Other: atherosclerosis, blood pressure, arteriovenous malformation B. Hemorrhage 33% Transient episode of neurological dysfunction caused by focal CNS ischemia without acute infarction..

11 Ischemic Penumbra Surrounding the core region of infarction is an impaired area of reduced blood flow- ischemic penumbra - which will eventually infarct if blood flow is not restored. Metabolic, electrical, and neurochemical processes are altered in the penumbra leading to impaired function. The infarcted area is damaged irreversibly, but the ischemic penumbra can be rescued in time-dependent manner. The infarcted area and the ischemic penumbra both contribute to the functional deficits of stroke. Goal of neuroprotection is to rescue the ischemic penumbra.

12 Pericytes Regulate Cerebral Blood Flow Neuronal activity cerebral blood flow Basis of fmri and most PET imaging Neuronal activity causes Glu release from terminals. Glu binds to NMDA receptors on pericytes surrounding brain capillaries, causing pericytes to relax, and a subsequent increase in diameter of capillaries. Ischemia causes pericytes to constrict, which reduces blood supply to the affected area. As pericytes die, they remain in a constricted state, reducing the possibility of restoring blood flow and leading to further neuronal death.

13 The origin and distribution of the blood supply to : 1. Cerebral Hemispheres 2. Brainstem 3. Spinal Cord

14 Origin of Blood Supply 1. Internal carotid arises from common carotid 2. Vertebral arises from subclavian

15 Internal carotids and vertebrals anastomoze in the Circle of Willis Superficial branches supply the surface, penetrating branches supply deep structures Circle of Willis Collateral circulation within the Circle of Willis occurs under some situations and can prevent infarction.

16 Origin of Blood Supply Anterior: Internal carotids supply hemispheres and eye via: middle cerebral anterior cerebral anterior choroidal ophthalmic artery Posterior: vertebrals supply hemispheres, brainstem, spinal cord, cerebellum: posterior cerebral superior cerebellar basilar posterior inferior cerebellar anterior inferior cerebellar ant/post spinal Ant Cerebral Art Middle Cerebral Art Post Cerebral Art Anterior circulation Posterior circulation

17 Anterior / Posterior Cerebrals Post Cerebral Art Ant Cerebral Art

18 A C A I Middle Cerebral M C A Middle Cerebral Art Occlusion of specific branches results in symptom clusters

19 ACA ICA ACA MCA MCA Lateral View Anterior-Posterior View

20 Lenticulostriate Arteries Small, penetrating branches of MCA supply Putamen Globus Pallidus Infarcts produce focal deficits Lenticulostriate arteries

21 Other Structures Supplied IC: eye (ophthalmic a.) ACA: corpus callosum Anterior choroidal: choroid plexus, hippocampus, amygdala, optic tract, lateral geniculate, Meyer s loop, glob. pallidus, internal capsule

22 Deep Structures Int.Cap Caudate Putamen Globus Pall. Thalamus Hypothalamus IC, ACA, MCA, Ant Chor, Post Comm MCA, (ACA) MCA via lenticulostriate, Ant Chor PCA PCA, Post Comm, ACA MCA ACA coronal PCA

23 Supply to Brainstem anterior cerebral anterior communicating internal carotid middle cerebral anterior choroidal posterior cerebral superior cerebellar basilar labyrinthine anterior inferior cerebellar posterior communicating Cerebellum:PICA, AICA, SCA posterior inferior cerebellar vertebral anterior spinal posterior spinal Blood supply to the brainstem is crucial for function of sensory and motor pathways. Infarcts can have drastic consequences. To help you remember this blood vessel diagram, you will be required to draw it on the brainstem for exam 3.

24 Supply to Medulla posterior spinal PICA anterior spinal vertebral anterior spinal vertebral

25 Supply to Pons Basilar Overlapping supply: AICA, sup cerebellar One or the other may supply this territory long circumferentials short circumferentials basilar paramedian Paramedian and circumferentials are general terms based on position or length. These are branches of the basilar artery.

26 Supply to Midbrain Posterior cerebral long circumferential (or superior cerebellar) basilar posterior cerebral artery paramedian branch of PCA short circumferential The end of the basilar artery bifurcates into right and left posterior cerebral arteries.

27 Loss of blood supply for any branch will affect specific structures in the vessel s territory. 1. specific sensory/motor symptoms 2. motor cranial nerve nuc/fibers can be in same territory as CST, causing alternating hemiplegia 3. cranial nerve symptoms indicate brainstem localization (not I, II, XI)

28 Supply to Spinal Cord anterior and posterior spinal arteries are reinforced by radicular arteries. Anterior spinal Few feeder arteries = more vulnerable to infarct Posterior spinal Many feeder arteries = less vulnerable to infarct

29 Supply to Spinal Cord Posterior spinal Anterior spinal

30 Anterior Spinal Artery Alternating branches to LT and RT. Blockage of a branch can cause infarct on one side of the spinal cord.

31 Venous System Superficial/Deep cerebral veins Dural venous sinuses Internal Jugular vein

32 Blood vessels tutorials on the web site: Territories and pathway structures Angiograms AND lesions localization tutorial on the Temple Univ web site (see link on Exams pg)