Cerebral Hemispheres & Vascular Supply Flashcards
Main Functional Areas of Cerebral Cortex
Circle of Willis
- Arterial supply to the cerebral hemispheres.
- An anastomotic ring giving collateral circulation.
- Anterior circulation.
- From brachial cephalic trunk or aorta > internal carotid aa.
- Posterior circulation.
From subclavian aa. > transverse foramen / vertebral aa. > basilar arter
Anterior & Posterior Circulation
Anterior & Posterior Circulation
Main Arteries of the Circle of Willis
- Anterior cerebral artery (ACA).
- Anterior communicating aa. (AComms) link the ACAs.
- Middle cerebral artery (MCA).
- Posterior cerebral artery (PCA).
- Arise from the top of the basilar a.
Main Arteries of the Circle of Willis
- The anterior & posterior circulations are linked via the posterior communicating aa. (PComms).
- PComms connect internal carotids to PCA.
- Brainstem branches & cerebellar aa. arise from basilar a.
Figure 10.3 Circle of Willis and Its Main Branches
Internal Carotid Artery
- Named segments.
- Cervical segments.
- Petrous segment.
- Cavernous segment (carotid siphon).
- Passes anterior clinoid process to pierce dura & bed posterior to subarachnoid space as intracranial segment.
Circle of Willis and Its Main Branches
Circle of Willis and Its Main Branches
Main Branches of Intracranial Segment of Internal Carotid Artery
- OPAAM
- Ophthalmic a. - enters optic foramen with optic n.
- Posterior communicating a.
- .Anterior choroidal a.
- Anterior cerebral a.
- Middle cerebral a.
Territories of 3 Main Cerebral Aa.
Superficial Cerebral Structures
- ACA (anterior cerebral artery) travels in interhemispheric fissure and back over corpus callosum.
- Supplies most of cortex on anterior medial surface from frontal > parietal lobes & medial sensorimotor cortex.
Anterior Cerebral Artery
Arteries of the Brain
Territories of 3 Main Cerebral Aa.
Superficial Cerebral Structures
•MCA turns laterally & enters Sylvian fissure.
Territories of 3 Main Cerebral Aa.
Superficial Cerebral Structures
- MCA turns laterally & enters Sylvian fissure ad then bifurcates into
- Superior division
- Inferior division
- (varies, sometimes into 3 or 4).
The branches form a loop as they pass over the insula and back out Sylvian fissure.
Middle Cerebral Artery -MCA
Arteries of the Brain
Territories of 3 Main Cerebral Aa.
Superficial Cerebral Structures
- PCA curves back with branches over:
- Inferior & middle temporal lobe
- Occipital cortex.
Arteries of the Brain
Arteries of the Brain
Territories of 3 Main Cerebral Aa.
Superficial Cerebral Structures
- MCA turns laterally & enters Sylvian fissure ad then bifurcates into
- Superior division
- Inferior division
- (varies, sometimes into 3 or 4).
- The branches form a loop as they pass over the insula and back out Sylvian fissure.
Territories of 3 Main Cerebral Aa.
Deep Cerebral Structures
- **MOST IMPORTANT penetrating vessels at the base of brain = lenticulostriate aa.
- Arise from MCA.
- Penetrate anterior perforated substance.
- Supply large part of basal nuclei (ganglia) & internal capsule.
- Prone to narrowing in HTN > infarct > rupture
> hemorrhage.
Figure 10.7 Lenticulostriate Arteries
Territories of 3 Main Cerebral Aa.
Deep Cerebral Structures
- Anterior choroidal a. arises from internal carotid aa.
- Globus palladus, putamen, thalamus, (lateral geniculate nucleus?), posterior limb internal capsule (corticospinal & corticobulbar tracts).
- Infarct of lenticulostriate or anterior choroidal aa. territories often=contralateral hemiparesis.
Figure 10.8 Blood Supply to Deep Cerebral Structures (Part 1)
Figure 10.8 Blood Supply to Deep Cerebral Structures (Part 2)
Territories of 3 Main Cerebral Aa.
Deep Cerebral Structures
- Branches of ACA.
- Recurrent a. of Heubner.
- Supplies head of caudate nucleus, anterior putamen, globus palladus & internal capsule.
- Thalamoperforator aa.
- Thalamus & maybe post. limb int. capsule.
Figure 10.9 Summary of Superficial and Deep Blood Supply to the Cerebral Hemispheres (Part 1)
Figure 10.9 Summary of Superficial and Deep Blood Supply to the Cerebral Hemispheres (Part 2)
Clinical Syndromes
- MCA infarct & ischemia is common - and more common than ACA & PCA.
- MCA in 3 regions:
- Superior division.
- Inferior division.
- Deep territory.
- Aphasia, hemineglect, hemianopia, face-arm or face-arm-leg sensorimotor loss.
-Gaze toward side of lesion acutely
Major Clinical Syndromes of the MCA
Major Clinical Syndromes of the MCA
Clinical Syndromes
- ACA
- UMN lesion weakness & cortical type sensory loss affecting contralateral leg more than face or arm.
- Large ACA stroke can give contralateral hemiplegia.
Major Clinical Syndromes of the MCA, ACA, PCA
Clinical Syndromes
•PCA
. Contralateral homonymous hemianopia.
•Small penetrating branch can infarct thalamus, posterior limb of internal capsule with sensory loss, contralateral hemiparesis or a thalamic aphasia (so can mimic MCA).
Watershed Infarcts
- When blood supply to 2 adjacent arteries are compromised, region between 2 vessels are susceptible to ischemia/infarct.
- Watershed zone.
- Bilateral watershed infarcts in both ACA-MCA & MCA-PCA watershed zones can occur with severe drop in systemic BP.
- Occlusion of internal carotid a. or drop in BP in patient with carotid stenosis can cause ACA-MCA watershed infarct.
Watershed Infarcts
- Proximal arm & leg weakness (“man in a barrel syndrome”).
- In dominant hemisphere – transcortical aphasia syndromes.
- MCA-PCA infarct can cause higher order visual processing.
Figure 10.10 Watershed Zones for the Major Cerebral Arteries
Transient Neurological Episodes
- Common, motor, somatosensory, visual, auditory, olfactory, kinesthetic, emotional, or cognitive.
- Most common causes:
- Transient ischemic attack (TIA).
- Migraine.
- Seizure.
- Cardiac arrhythmia.
- Hypoglycemia.
TIA
- Neurological deficit lasting less than 24 hours.
- Most typical less than 10 minutes.
- More than 10 minutes; some permanent cell death.
- More than 1 hour usually small infarct; sometimes complete functional recovery within 24 hours.
- Caused by temporary brain ischemia.
- ** Warning sign.
- Neurological emergency.
TIA
- 15% will have a stroke within 3 month with persistent deficits.
- ½ of these occur within 48 hours.
- Urgent referral, admittance, & evaluation for treatment.
- 15% will have a stroke within 3 month with persistent deficits.
- ½ of these occur within 48 hours.
- Urgent referral, admittance, & evaluation for treatment.
- Without other focal features…
- Most commonly by cardiogenic syncope.
- Vasovagal transient episodes of hypotension.
- Arrhythmias.
- Other non-neurogenic causes.
- Neurologic causes:
- Seizures.
Ischemic Stroke
- 3rd leading cause of death in U.S.A.
- Major cause of permanent disability.
- Acute diagnostic & therapeutic management essential, treated like severity of cardiac emergencies.
- Ischemic strokes can lead to hemorrhagic conversion.
- Inadequate blood supply causing tissure death.
- Embolic infarct.
- Thrombotic infarct.
Common Stroke Risk Factors
Carotid Auscultations
Circle of Willis
- Complete the following learning module on the Circle of Willis.
- http://www.neuroanatomy.ca/flex_labs/Circle_Willis/story_html5.html
Ischemic Stroke
(Use Blumenfeld pp 405 - 409.)
- For the following, define & discuss the mechanisms of pathology:
- Embolic infarcts & cause.
- Thrombolic causes and mechanism.
- Large vessel infarct.
- Small vessel / lacunar infarct.
- Cortical vs. subcortical.
- Hemispheric vs. brainstem lesions.
- Stroke risk factors.
- Treatment & diagnostic workup.
Stenosis & Dissection, Thrombosis
(Use Blumenfeld pp 410 – 411, 413.)
- For the following, define & discuss the mechanisms of pathology:
- Carotid stenosis.
- Dissection of the carotid & vertebral aa.
- Sagittal sinus thrombosis.
