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

The brain receives arterial blood from two sources.

What are they?

Answer 2

1. The anterior circulation is fed by the internal carotid arteries and supplies most of the cerebral hemispheres
2. The posterior circulation is fed by the vertebral arteries and supplies the brainstem, cerebellum, some of the temporal lobe and the occipital lobe

Question 3

Memorise this layout of blood supply to the brain

Answer 3

Question 4

Observe the images

Answer 4

Question 5

What makes up the anterior circulation?

Answer 5

Middle cerebral artery

Anterior cerebral artery

Question 6

What is the middle cerebral artery?

Answer 6

The direct continuation of the internal carotid artery

Question 7

What does the middle cerebral artery supply?

Answer 7

• Cortical branches emerge from the lateral fissure to supply the lateral aspect of the cerebral hemisphere (cortex and underlying white matter), including lateral parts of the frontal and parietal lobes as well as the superior temporal lobe
• Deep branches (the lenticulostriate arteries) supply deep grey matter structures including the lentiform nucleus and caudate as well as the internal capsule

Question 8

What are the lenticulostriate arteries?

Answer 8

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

Question 9

What is the anterior cerebral artery a branch of?

Answer 9

A branch of the internal carotid artery

Question 10

What does the anterior cerebral artery supply?

Answer 10

• The vessels loop over the corpus callosum and send branches to the adjacent cortex
• Cortical branches supply the medial aspect of the frontal and parietal lobes (not the occipital lobe)
• There are also branches to the corpus callosum itself

Question 11

How is the anterior communicating artery formed?

Answer 11

The left and right anterior cerebral arteries anastomose in the midline via the anterior communicating artery

Question 12

The vertebro-basilar system is the main distribution network for the posterior circulation.

Observe this image and learn.

Answer 12

Question 13

What makes up the posterior circulation?

Answer 13

Basilar artery

The vertebral arteries

Question 14

How is the basilar artery formed?

Answer 14

Midline vessel formed from the confluence of the vertebral arteries

Question 15

What does the basilar artery gives rise to?

Answer 15

Posterior cerebral artery (this goes on to give rise to posterior communicating arteries)

Superior cerebellar artery

Pontine arteries

Anterior inferior cerebellar artery

Question 16

What does the posterior cerebral artery supply?

Answer 16

Supplies occipital lobe, inferior temporal lobe and thalamus (via thalamoperforator and thalamogeniculate branches)

Also supplies midbrain en passant

Question 17

What does the posterior communicating arteries supply?

Answer 17

Posterior communicating arteries branch from the posterior cerebral arteries to connect with the anterior circulation (internal carotid artery)

Question 18

What does the superior cerebellar artery supply?

Answer 18

supplies the superior aspect of the cerebellum and midbrain en passant

Question 19

What does the pontine arteries supply?

Answer 19

Supplies the pons (including the descending corticospinal fibres)

Question 20

What does the anterior inferior cerebellar artery supply?

Answer 20

Anterior inferior cerebellar artery the supplies the antero-inferior aspect of the cerebellum and lateral pons en passant

Question 21

The vertebral arteries gives rise to 2 important branches to the brain. What are they?

Answer 21

Anterior spinal arteries

Posterior inferior cerebellar arteries

Question 22

What does the anterior spinal arteries supply?

Answer 22

Anterior spinal arteries converge in the midline to supply the anterior 2/3 of the spinal cord

Question 23

What does the posterior inferior cerebellar arteries supply?

Answer 23

Posterior inferior cerebellar arteries supply the postero-inferior aspect of the cerebellum en passant

Question 24

What is the Circle of Willis?

Answer 24

• 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 25

Describe the anatomical course of the internal carotid artery

Answer 25

⇒ 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 26

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 26

- **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 27

Describe the anatomical course of the vertebral arteries

Answer 27

⇒ 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 28

Within the cranial vault, the vertebral artery gives rise to three branches. Identify these branches as well as the respective region they supply

Answer 28

- **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 29

There are three main paired constituents of the Circle of Willis. Identify them as well as their origins

Answer 29

- **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 30

To complete the circle, there are two connecting vessels present. Identify these as well as their role

Answer 30

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

Question 31

There are three cerebral arteries. Identify them as well as the respective portion of the cerebrum that they supply

Answer 31

- **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 32

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 32

- **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 33

What supplies the spinal cord?

Answer 33

Anterior spinal artery Paired posterior spinal arteries (Both fed with blood from **segmental vessels from the aorta** but also at the top of the cord, anterior spinal artery also arises from the **convergence of the 2 vertebral arteries**.: these also feed into the spinal cord supply)

Question 34

What does the anterior spinal artery supply?

Answer 34

It runs along the midline of the anterior sulcus of the spinal cord. It supplies the **anterior ⅔ of the spinal cord** This includes **ventral horn, corticospinal tract and spinothalamic tract**.: supplies most of the important pathways in the spinal cord.

Question 35

What does the posterior spinal arteries supply? - REMEMBER THERES 2 .: THEY SUPPLY EACH SIDE OF THE SPINAL CORD

Answer 35

Supplies the **posterior ⅓ of the spinal cord** It supplies the **dorsal column pathways and some/most of the dorsal horns.**

Question 36

What is the Artery of Adamkiewicz?

Answer 36

Major blood supply to lower part of the spinal cord Esp vulnerable in aortic aneurysm repairs → can lead to spinal cord syndromes if damaged

Question 37

If the anterior spinal artery vs posterior spinal arteries gets blocked, what happens?

Answer 37

**ASA** → midline vessel .: BILATERAL EFFECTS .: would lead to loss of STT modalities below level of blockage. Also upper motor neurone signs below level of blockage due to interruption with CST. **PSA** → less commonly blocked but if they do get blocked → commonly UNILATERAL EFFECTS (one of the arteries affected) instead of bilateral (remember they are paired arteries) If 1 only gets affected → gets IPSILATERAL dorsal column modalities below level of lesion

Question 38

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 38

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

Question 39

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 39

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

Question 40

What is the great anterior segmental artery of Adamkiewicz?

Answer 40

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 41

What is a stroke?

Answer 41

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

Question 42

There are four main causes of a cerebrovascular accident. Identify and describe them

Answer 42

- **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 43

What is the most common cause of a cerebrovascular incident?

Answer 43

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

Question 44

What is an aneurysm?

Answer 44

- 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 45

What is a spinal cord infarction?

Answer 45

- 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 46

What are the most common causes of spinal infarction?

Answer 46

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

Question 47

What supplies the spinal cord?

Answer 47

* **Anterior spinal artery** * **Paired posterior spinal arteries** (Both fed with blood from **segmental vessels from the aorta** but also at the top of the cord, anterior spinal artery also arises from the **convergence of the 2 vertebral arteries**.: these also feed into the spinal cord supply)

Question 48

Label the cerebral vasculature on this image.

Answer 48