S4) Blood Supply to the Brain

Question 1

There are two paired arteries which are responsible for the blood supply to the brain.

What are they?

Answer 1

• Vertebral arteries
• Internal carotid arteries

Question 2

What is the Circle of Willis?

Answer 2

• The Circle of Willis is the anastomotic circle formed from the terminal branches of the ICA and vertebral arterie
• From this circle, branches arise which supply the majority of the cerebrum

Question 3

Describe the anatomical course of the internal carotid artery

Answer 3

⇒ Originates at the bifurcation of the common carotid artery (C4)

⇒ Move superiorly within the carotid sheath

⇒ Enter the brain via the carotid canal of the temporal bone

⇒ Pass anteriorly through the cavernous sinus

Question 4

Distal to the cavernous sinus, the internal carotid artery gives rise to four branches.

Identify these branches as well as the respective region they supply

Answer 4

• Ophthalmic artery – supplies structures of the orbit
• Posterior communicating artery – acts as an anastamotic connecting vessel in the CoW
• Anterior cerebral artery – supplies part of the cerebrum
• Middle cerebral artery – supplies the lateral portions of the cerebrum

Question 5

Describe the anatomical course of the vertebral arteries

Answer 5

⇒ Originates from the subclavian artery (medial to anterior scalene muscle)

⇒ Ascends up the posterior side of the neck, through the foramen transversarium

⇒ Enters the cranial cavity via the foramen magnum

⇒ Gives off branches, then converge to form the basilar artery

Question 6

Within the cranial vault, the vertebral artery gives rise to three branches.

Identify these branches as well as the respective region they supply

Answer 6

• Meningeal branch – supplies the falx cerebelli
• Anterior and posterior spinal arteries – supplies the spinal cord, spanning its entire length
• Posterior inferior cerebellar artery – supplies the cerebellum

Question 7

There are three main paired constituents of the Circle of Willis.

Identify them as well as their origins

Answer 7

• Anterior cerebral arteries – terminal branches of the internal carotid arteries
• Internal carotid arteries – immediately proximal to the origin of the middle cerebral arteries
• Posterior cerebral arteries – terminal branches of the vertebral arteries

Question 8

To complete the circle, there are two connecting vessels present.

Identify these as well as their role

Answer 8

• Anterior communicating artery: connects the two anterior cerebral arteries
• Posterior communicating artery: connects the ICA to the posterior cerebral artery

Question 9

There are three cerebral arteries.

Identify them as well as the respective portion of the cerebrum that they supply

Answer 9

• Anterior cerebral arteries – supply the anteromedial portion of the cerebrum
• Middle cerebral arteries – supply the majority of the lateral part of the brain
• Posterior cerebral arteries – supply both the medial and lateral parts of the posterior cerebrum

Question 10

The spinal cord is primarily supplied by three longitudinal arteries, as it descends from the brainstem to the conus medullaris.

Identify them as well as their origins

Answer 10

• Anterior spinal artery – formed from branches of the vertebral arteries and travel in the anterior median fissure, terminating as sulcal arteries
• Two posterior spinal arteries – originate from the vertebral artery / the posteroinferior cerebellar artery, anastomosing in the pia mater

Question 11

Below the cervical level, longitudinal arteries offer insufficient blood supply. There is support via anastomosis with the segmental medullary and radicular arteries.

Describe the location of the segmental medullary arteries

Answer 11

Anterior and posterior segmental medullary arteries originate from spinal branches of many of arteries, then enter the vertebrae through the intervertebral foramina

Question 12

Below the cervical level, longitudinal arteries offer insufficient blood supply. There is support via anastomosis with the segmental medullary and radicular arteries.

Describe the regions supplied by the radicular arteries

Answer 12

• The radicular arteries supply the anterior and posterior nerve roots
• Some radicular arteries may also contribute to supplying the spinal cord

Question 13

What is the great anterior segmental artery of Adamkiewicz?

Answer 13

The great anterior segmental artery of Adamkiewicz reinforces circulation to the inferior 2/3 of the spinal cord, and is found on the left in the majority of individuals

Question 14

What is a stroke?

Answer 14

A stroke is an acute development of a neurological deficit, due to a disturbance in the blood supply of the brain

Question 15

There are four main causes of a cerebrovascular accident.

Identify and describe them

Answer 15

• Thrombosis – obstruction of a blood vessel by a locally forming clot
• Embolism – obstruction of a blood vessel by an emboli formed elsewhere
• Hypoperfusion – lack of blood supply to the brain, due to systemically low blood pressure e.g shock
• Haemorrhage – an accumulation of blood within the cranial cavity

Question 16

What is the most common cause of a cerebrovascular incident?

Answer 16

Embolism – in many patients, an atherosclerotic emboli will arise from the vessels of the neck

Question 17

What is an aneurysm?

Answer 17

• An aneurysm is a dilation of an artery, which is greater than 50% of the normal diameter
• They are most likely to occur to occur in the vessels contributing to the Circle of Willis

Question 18

What is a spinal cord infarction?

Answer 18

• A spinal cord infarction (aka spinal stroke) refers to the death of nervous tissue, which results from an interruption of the arterial supply
• Clinical signs include muscle weakness, paralysis and loss of reflexes

Question 19

What are the most common causes of spinal infarction?

Answer 19

• Vertebral fractures/dislocations
• Vasculitic disease
• Atheromatous disease
• External compression e.g. abdominal tumours

Question 20

What are the lenticulostriate arteries?

Answer 20

The lenticulostriate arteries are small, deep penetrating arteries which branch from the middle cerebral artery