Lecture 4: The Blood Supply to the Brain Flashcards
Give causes of focal cerebral lesions in order of how common they are.
Common causes of neurological deficit are of vascular origin such as stroke. Other causes include tumours (primary or secondary), abscess or hydrocephalus. Vascular causes include:
- Transient Ischaemic Attack TIA - Stroke - neurological deficit of vascular origin lasting more than 24 hours. It may be due to an infarction or haemorrhage. It affects 1 in 100 people over 65.
Give the path of the Internal Carotid artery.
They emerge lateral to either side of the optic chiasm. The first branch of the internal carotid is called the middle cerebral artery. This is paired artery suppling the middle aspect of the cerebrum. The next branch is the anterior cerebral artery. These are paired arteries that tuck under the midline portion of each hemisphere to supply its anterior and medial arch.
Give the path of the Vertebral artery.
The vertebral arteries come up through the foreman magnum. They are a branch of the subclavian artery. They give the posterior inferior cerebella artery (PICA). It supplies the posterior and inferior surface of the cerebellum. It also gives off the anterior spinal artery. There is only one ASA. It descends all the way down the leg of the spinal cord to supply the anterior aspect of the spinal cord.
The origin of the posterior spinal artery is quite variable - in some it comes from the PICA whereas in other it comes from the vertebral artery.
The anterior inferior cerebella artery is a pair of arteries from the vertebral artery that supplies the anterior inferior aspect of the vertebral artery. It is here the vertebral arteries fuse to form the Basilar artery. This gives rise to many transverse pontine branches to supply the anterior aspect of the pons. The Basilar artery gives rise to the superior cerebellar artery to go and supply the superior aspect of the cerebellum. The terminal branch of the basilar artery is one on each side and will supply the posterior aspect of the cerebrum. This is known as the Posterior Cerebral Artery. There is 3 pairs of cerebella arteries from this system: PICA, AICA and SCA. There is a also posterior cerebral artery.
How is the circle of Willis formed?
The circle of Willis joins the Vertebral basilar system and the Internal carotid. Joining the two anterior cerebral arteries is an anterior communicating artery. The posterior communicating artery, which is also paired, connects the PCA and internal carotid.
The Circle of Willis surrounds the optic chiasm and hypothalamus. It ensures compensation of decreased blood flood if one vessel is occluded.
What is a berry aneurysm?
Aneurysms happen when there is a weakening of the wall of the blood vessel. They happen more frequently in an area where there is branching. The circle of Willis is highly branching, this is a common site of aneurysms. 10% of vascular strokes are caused by rupture of a berry aneurysm. This is a surgical emergency. It can lead to subarachnoid bleeding and so a subarachnoid haemorrhage.
What is the relationship between cranial nerves and blood supply?
There is a close relationship between the blood vessels and cranial nerves. A blockage/rupture of the blood vessels can lead to functional impairment of the nerves supplied by those blood vessels.
What are the territories of cerebral arteries?
Anterior Cerebral Artery (ACA) - The superior and medial areas of the frontal and parietal lobes. It also supplies the Corpus Callosum.
Middle Cerebral Artery (MCA) - Supplies the lateral aspects of the frontal, temporal and partial lobes.
Posterior Cerebral Artery (PCA) - Occipital Lobe and inferior/medial surface of the temporal lobe
What are striate arteries?
There are deep or perforating arteries, some of which are called striate arteries. These supply structures inside the hemisphere:
- Deep nuclei - Deep grey matter - Internal capsule (major fibre bundle to and from the cerebral cortex) - Supply includes major descending motor pathway.
These lateral striate arties branch from the MCA. They supply the grey matter structures, basal ganglia (thalamus for example) and the white matter (internal capsule). If we have blockage of the little striate arteries we can have neurological deficit arising from areas supplied by the internal capsule (such as a descending motor pathway).
What are watershed areas?
These are regions that receive blood supply from distal areas of adjacent cerebral arteries. Distal branches of the ACA and MCA for example both supply an overlapping ACA-MCA watershed area. If there is a drop In systemic blood pressure, not enough blood will reach those watershed areas and so they are prone to stroke.
How is venous drainage established in the brain?
Superficial veins drains straight into the Dural sinuses
Deep veins drain into the great cerebral vein. Drain internal structures of the brains such as the thalamus, basal ganglia and corpus callosum. Once in the GCV they drain into the straight sinus and ultimately into the Confluence of Sinuses.
Why is damage to the cavernous sinus particularly dangerous?
Multiple structures are related to the cavernous sinus. There is easily a spread of infections. The pituitary gland sits very closely to it. There are paranasal sinuses within the sphenoid bone in very close proximity. Any infection in these sinuses can spread to the sinuses. There is the optic chiasm superiorly and loads of cranial nerves. Any infections that reach the cavernous sinus can affect all of these structures.
What is the danger triangle of the face?
Infection can also reach the sinus through a cut in the danger triangle of the face. The facial vein that drains that area of the face has direct communication with the cavernous sinus of the face.
If infection reaches here we can have meningitis or thrombosis of the cavernous sinus - headaches, oedema of the eyeball, numbness of the face and palsies of cranial nerves.
Give a common vascular cause of a:
(a) Epidural haemorrhage
(b) Subdural haemorrhage
(c) Subarachnoid haemorrhage
(a) A torn meningeal artery we create a separation between the skull and an haemorrhage - epidural haemorrhage. The dura since separated follows the control of the brain. They have a characteristic long shape.
(b) A torn bridging artery leads to a subdural haemorrhage. If they tear there is a pathological space between the dura and the arachnoid. They have a characteristic crescent shape and a shift on the Falx cerebri. These haemorrhages cannot cross to the other side. They are limited by the falx and Tentorium cerebelli. There is a characteristic compression of the ventricles as it acts as a mass, compressing the CSF.
(c) A torn cerebral artery lead to a subarachnoid haemorrhage - ACA, PCA etc. These are located in the subarachnoid space and so we see blood here.
Give the location of the following sinuses:
(a) Superior Saggital sinus
(b) Inferior Saggital Sinus
(c) Straight Sinus
(d) Transverse Sinuses
(e) Confluence of Sinuses
(f) Cavernous Sinus
(a) The Superior Sagittal sinus - Travels around the attachment border of the Falx Cerebrum. It empties into the Confluence of Sinuses at the back.
(b) The inferior Sagittal Sinus travels parallel to the Superior Sagittal Sinus and travels along the free edge of the Falx Cerebri and drains into the Falx Cerebellii to drain tonto the straight Sinus.
(c) The straight sinus is attached found where the Falx Cerebelli and Tentorium Cerebelli meet. It then empties its blood into the Confluence of Sinuses.
(d) There are paired transverse sinuses and travel along the attachment of the tentorium Cerebelli. The transverse sinuses bend in in a S shape to become the sigmoid sinus.
(e) The Confluence of sinuses is the meeting point of all the sinuses - The Superior sagittal, straight and transverse sinuses meet.
(f) The cavernous sinus is located lateral to the body of the sphenoid bone.
What are bridging veins?
This is how the superficial cerebral veins that empty into the superior sagittal sinus. They briefly pierce the arachnoid to pierce into the superior sagittal sinus.
