Arterial Blood Supply to the Brain

Question 1

Blood supply to the brain derived from which major vessels, and to what extent does each contribute to overall blood supply?

Answer 1

Internal Carotid Arteries (~80%)
Vertebral Arteries (~20%)

Question 2

Describe the IC’s course to the circle of willis

Answer 2

Arises from common carotid in neck (just superior from where carotid pulse is felt) -> enters skull via carotid canal, just superior to the foramen lacerum -> travels through cavernous sinus lateral to sella turcica -> passes medial to anterior clinoid process -> gives rise to Opthalmic Artery before contributing to arteries of the circle of willis

Question 3

What vessels does the ICA give rise to in the cranium?

Answer 3

1. Opthalmic
2. Anterior Choroidal
3. Bifurcates into the Anterior and Middle Cerebral Arteries

Question 4

What areas are supplied by Opthalmic artery?

Answer 4

Contents of the orbit

Question 5

Areas supplied by anterior choroidal artery

Answer 5

Optic Tract
Lateral Choroid Plexus
Hippocampus
Much of Globus Pallidus and Internal Capsule

*Quite susceptible to thrombotic strokes

Question 6

Areas supplied by Anterior Cerebral Artery

Note important parts

What specific part of motor and somatosensory homonculus ?

Answer 6

Most medial Portions of the Frontal and medial portaions of anterior area of Parietal Lobes.
Cingulate Gyrus
Corpus Callosum.

“Leg portion” of homunculus

Question 7

Areas Supplied by Middle Cerebral Artery?

Note important parts

Portion of Homunculus?

Answer 7

Largest of the 3 cerebral aa

Whole lateral surface of Frontal, Parietal and Temporal Bloes.

Includes Auditory cortex. Broca’s and Wernicke’s Areas (usually in left hemisphere)

Supplies for whole body except legs of homunculus

Question 8

Course of the Vertebral Artery to produce the posterior circulation

Answer 8

Arises from Subclavian Artery -> Travels through transverse framina of the cervical vertebrae -> Enters Skull through Foramen Magnum -> Ascend ventral medulla -> Fuse (forming basilar) at pontomedullary junction

Question 9

Vessels given off by vertebral arteries

Answer 9

Prior to fusion: Posterior Inferior Cerebellar Artery (PICA) and Anterior and Posterior Spinal Arteries

Then fuses to form the Basilar Artery -> gives off multiple small branches which supply the brainstem and other structures -> Chiefly gives rise to the:

• Anterior Inferior Cerebellar Artery (AICA) and Interior Auditory Artery ‘(emerge flanking CNVI and medulla-pons junction)
• Superior Cerebellar Artery (SCA) just before bifurcating into the…

Posterior Cerebral Arteries (PCA) (these arteries surround CNIII at the pons-midbrain junction)

Question 10

Overall, what structures does the ‘posterior circulation’ (aka vertebrobasilar system) supply?

Answer 10

Cervical Spinal Cord
Most of Brainstem
Cerebellum
Much of Occipital Lobe
Inferior Temporal Lobe

Question 11

Describe the location of the circle of willis

Answer 11

Base of the brain, encircling the optic chiasma and ventral surface of the hypothalamus and midbrain

Question 12

Which arteries contribute to the circle of willis?

Answer 12

Anterior, Middle (from ICA) and Posterior (from vertebeal/basilar) Cerebral Arteries

Linked by Anterior and Posterior Communicating Arteries

Question 13

Areas supplied by the PCA

Important areas?

Answer 13

Passes posteriorly around midbrain
Supplies much of interior surface of temporal lobe
Medial Border of Parietal and Occipital Lobes
*Primary visual cortex along calcarine fissure

Question 14

Stroke affecting distribution of MCA’s area might present with?

Answer 14

Auditory cortex: hearing impairments

Broca’s and Wernicke’s area (usually in L hemisphere): speech impairments/aphasia

Everything except leg on homunculus -> But on contralateral side weakness/decreased sensation etc. -> depending on location

Question 15

Stroke Affecting ACA may present with?

Answer 15

Paralysis/Weakness and Loss of Sensation in contralateral Leg/Foot

Loss of Frontal Lobe Reflexes - e.g. sucking reflex, grasping reflex.

Abulia (lack of will/motivation - e.g. social withdrawal, passivism, being quiet) or (spectrum) to extent of Akinetic Mutism (lack of will to move or speak)

Question 16

Stroke Affecting PCA?

Answer 16

Peripheral areas: Cortical blindness, visual agnosia, anomic aphasia, homonymous hemaniopia (half-visual field loss in both eyes. But loose the same half of vision in both eyes…).

Medial Areas: 
Central post-stroke (thalamic) pain
Dysthesias, sensory loss
Occulomotor nerve palsy
Hemiplegia (paralysis of contralateral side arm, leg and trunk)

Question 17

Areas supplied by the Perforating (or central) Arteries and the Choroidal Arteries together?

Answer 17

Deep structures of the brain:
Basal Ganglia
Thalamus
Internal Capsule, etc.