Blood supply and stroke Flashcards
What is the general blood supply to the brain?
The circle of Willis supplies the internal carotid artery and basilar artery with blood which go on to supply the Forebrain (cerebrum and diencephalon)
The basilar artery supplies the vertebral arteries with some blood and these go on to supply the Hindbrain (Brain stem and cerebellum)
What are some features of the internal carotid artery ?
Internal carotid;
- Has several segments
- Originates at C3-4 at bifurcation of common carotid
- Travels in carotid sheath
- Enters base of skull via carotid canal
- Passes through petrous temporal bone emerges from internal opening of carotid canal
- Passes over foramen lacerum
- Passes through the cavernous sinus, piercing its roof at the anterior clinoid process, enters sub arachnoid space
- Gives off the ophthalmic artery first, followed by the posterior communicating and anterior choroidal artery
- Then bifurcates into the middle and anterior choroidal artery
- The bifurcates into middle and anterior cerebral arteries
- Then branches of the ICA thus make up the anterior circulation
What are some features of the vertebral arteries ?
- Vertebral’s are branches of the subclavian arteries
- Cours posterior-superiorly from the subclavian
- Enter deep to transverse process of C6/7, running in the transverse foramina of cervical vertebrae
- Pass across the posterior arch of C1 before entering the skull at the foramen magnum
- These give rise to anterior spinal arteries
What are the different parts of the vertebral artery (bits it can be split up into) ?
Vertebral artery;
- Suboccipital part
- Vertebral part
- Cervical part
What are some features of the basilar artery ?
Basilar Artery;
- Result of the union of vertebral arteries at the transition between the medulla and pons at the level of abducens nerve root
- Gives off branches to the pons, cerebellum, labyrinth and ultimately produce the posterior cerebral arteries
What arteries help to supply the hindbrain?
Vertebral supply from;
- Anterior spinal
- Posterior inferior Cerebellar (gives posterior spinal)
Basilar supply from;
- Pontine Arteries
- Superior cerebellar artery
- Anterior inferior cerebellar artery
- Labyrinthine artery
- Quadrigeminal artery
What are some features of the circle of Willis ?
The circle of Willis is an anastomotic network made from the meeting of the supply to the hindbrain and the forebrain
Anterior circulation - ICA
Posterior circulation - Basilar/vertebrals
Much variation exists however, which can -present with clinical implications
- Thought to be at increased risk of ischaemic stroke in variant anatomy of the Circle of Willis
What are some variants you can get in the Circle of Willis ?
Variants are most common in the posterior communicating and anterior cerebral arteries.
- Hypoplasia of one or both Posterior Communicating arteries about 30%
- Hypoplastic/absent A1 segment 15%
- Absent/fenestrated ACOM 12.5%
- Origin of Posterior Cerebral Artery (PCA) from Internal carotid artery (ICA) with absent/hypoplastic P1 segment 20%
- Infundibular dilation of PCOM - 10% (Posterior communicating artery)
What are the relations of the Circle of Willis?
The Circle of Willis forms around the optic chiasma and the vertebrals to the brain stem
What are features of the anterior cerebral supply?
The Anterior cerebral artery supplies the medial frontal and parietal lobes
Passes over corpus callosum and terminates close to the Pareto-occipital sulcus where it overlaps with branches of the posterior cerebral artery
Key structures, medial part of primary motor and somatosensory cortices, supplementary motor cortex, corpus callosum
What are features of the middle cerebral supply?
After giving off important cerebral branches to diencephalon passes along depth of lateral fissure of syvius
Lateral striate arteries are branches of the MCA, supply Corpus striatum, internal capsule and thalamus.
Supplies most of the frontal, parietal and temporal lobes and small part of occipital, supplying 2/3rds of lateral surface of brain
Key structures include most pre and post-central gym (primary motor and primary somatosensory cortices) pre frontal cortex, Wernicke’s area, Broca’s area, primary auditory cortex, insular cortex
What are features of the posterior cerebral supply?
Courses around midbrain with optic tract
Gives medial and lateral branches
Medially supplies the calcimine cortex (location of primary and visual cortex), cuneus and precious (basic visual processing/integration) and selenium of the corpus callosum (interloper somatosensory communication between parietal and occipital lobes)
Laterally - anterior/posterior temporal and occipital cortex
- Doesn’t supply motor function in cortex
What 4 things should you start to think about when asked about deficits?
Where is the deficit - arm, leg, face?
What type of deficit (sensory, motor, cognitive, integrative)?
Where does it lateralise to (left or right)?
Is it in ascending tract;
Spinothalamic (pain/temp, dorsal columns (fine/proprio)
or descending tracts;
Corticospinal (vol movement), rubrospinal (flexor tone) ?
What is the motor homunculus?
Graphical representation of the localisation of cortical motor control
Note that from lateral to medial the body is descended
Note that much space is given to movemens of face and hand but relative to lower limb
What artery supplies the territory responsible for the lower limbs?
The anterior cerebral artery ! (does medial 1/3d - lateral 2/3rd would be medial cerebral artery)
ACA strokes are more likely to affect the leg than the arm !
A patient is expriencing sudden onset right leg weakness and loss of sensation in the same leg, where is the lesion likely to be?
Since the patient has right leg weakness and right hemisensory loss the lesion is on the left hemisphere as the pathways (spinothalamic, dorsal columns and portico spinal) decussate and therefore the lesion is on the contralateral side.
We should consider that the primary motor and primary somatosensory cortices have been affected
The deficits are local to legs, no involvement of upper limb
- Medial aspect these cortices therefore we have medial aspect of primary motor and somatosensory cortices affected which are supplied by the anterior cerebral artery which means its likely he is having an ACA thrombotic event
A 62 year old woman with right arm and leg weakness, right arm sensory deficit with a slight facial droop, is found to have a problem with her speech. She speaks in short responses and her speech is slurred. Where is this ladies lesion?
Lady has dysarthria - due to disruption in the motor nerve supply to the face via the corticobulbar tracts/motor cortices
Expressive dysphasia - Broca’s area - inferior fontal gyrus
MCA and ACA territory to primary motor/somatosensory cortices
Where is language most commonly found?
Most people are LEFT hemisphere dominant and language is therefore localised to the left hemisphere
Where is language most commonly found?
Most people are LEFT hemisphere dominant and language is therefore localised to the left hemisphere
What are the 3 components of speech?
1). Generation;
- Non-fluent aphasia (inability to produce words and sentences mentality)
2). Articulation;
- Dysarthria (Speech sounds are slurred due to facial paresis)
3). Reception;
- Fluent aphasia (inability to understand the meaning of speech leads to inappropriate speech production - “word salad”
What is Broca’s Expressive Aphasia?
Th pattern of speech is clipped, one to two words but patient clearly understood words spoken to them. There is an inability t generate words and sentences but no issue with speech articulation, speech is also not inappropriate.
Where is Broca’s area found ?
Broca’s area is located in the inferior frontal gyrus (pars op and pars try) MCA supplies this
