Vasculature of the Brain Flashcards
What are the 2 types of stroke?
- Ischaemic Stroke (95%) due to an occlusion resulting in oxygen deficiency e.g. Embolism.
- Haemorrhagic Stroke (5%) either due to an aneurysm in the arterial circle or haemorrhage of small branches due to hypertension e.g. striate arteries or anterior choroidal artery
What are the branches of the Internal Carotid Artery? Where do the branches supply?
- Hypophyseal Arteries - Pituitary Gland. This branch then enters the hypophyseal portal system
- Ophthalmic Artery - End Artery of the Eye
- Anterior Choroidal Artery - Lateral Geniculate Nucleus, most distal part of the posterior limb and some Basal Ganglia
- Posterior Communicating Artery - This is the last branch
Note: The Middle Cerebral Artery is continuous with the termination of the ICA.
Where are the common places of an anterior circulatory ischaemic stroke?
- Common carotid artery
2. Internal carotid artery just after the bifurcation
Where are the common areas of a posterior circulatory ischaemic stroke?
- At the point where the vertebral artery branches from the subclavian artery
- The basillar artery (leads to brain stem syndromes)
What is the journey of the arterial anterior circulatory system to the brain?
- The first branch of the aortic arch becomes the brachiocephalic trunk which branches into the right common carotid artery and right subclavian
- The second branch of the aortic arch becomes the left common carotid artery
- The common carotid artery bifurcates at the level of C3
- The internal carotid goes deep into the infratemporal fossa and gives no branches to the face
- The ICA enters the carotid canal and then sits on the foramen lacerum
- The ICA enters the cavernous sinus
- The ICA hooks around the clinoid process of the sphenoid bone (look up)
- Gives off hypophyseal and opthalmic branches
- The ICA hooks around posteriorly to enter the arterial circle of willis
What is the journey of the arterial posterior circulatory system to the brain?
- The vertebral artery branches off the subclavian artery
- The vertebral artery travels vertically through six transverse foramina
- It then passes around the lateral mass of the atlas
- Pierces the atlantooccipital membrane
- Enters the subarachnoid space
- The vertebral artery passes through the foramen magnum with the spinal cord
- This then joins with the opposite vertebral artery, at the level where the medulla oblongata becomes the pons, to form the basillar artery
What are the smaller branches of the posterior circulatory system?
- Anterior spinal artery - from the top of the vertebral arteries
- Anterior inferior cerebellar arteries
- Pontine branches
- Superior cerebellar arteries
What are the consequences of a lesion to the posterior circulatory system?
- Alternating hemiplegia - where there is ipsilateral cranial nerve deficit but contralateral long tract deficit.
- Also, there will be brain stem syndromes. These include medial medullary syndrome, lateral medullary syndrome, locked in syndrome and top of basillar syndrome
Describe the features of medial medullary syndrome
-
Describe the features of lateral medullary syndrome (single vertebral artery stroke)
There is sparing of motor pathways as the Corticospinal Tract is medial and anterior to the Medulla Oblongata.
- Interruption VIII nuclei - vertigo, vomiting, nausea
- Ipsilateral Spinocerebellar pathway interruption - cerebellar ataxia due to dysfunction of unconscious proprioception
- Primary afferent fibres lesion of the V nerve in the spinal tract V - Ipsilateral deficit of crude touch, pressure, temperature and pain. Ipsilateral because there has not been decussation to the TTT
- Interruption to the descending sympathetic pathways from the hypothalamus (reticulospinal tract?) - Horner’s syndrome. This leads to miosis, slight ptosis, flushed dry face
- X and XI nuclei lesion - Laryngeal musculature deficit. Hoarseness of voice. Problems with swallowing
- Contralateral Spinothalamic tract lesion. Loss of contralateral pain and temperature sensation
Describe ‘Locked in’ syndrome
- There is Basilar artery stenosis or occlusion. This leads to total quadriplegia and a semi-vegetative state.
- The only possible movement is vertical motion of the eyes due to the medial longitudinal fasiculus pathway
Describe ‘Top of the basilar’ syndrome
This is due to occlusion of the top of the basilar artery which results in bilateral thalamic ischaemia. Features include:
- Cortical blindness
- Confabulations due to ischaemia to the Hippocampus, deep in the temporal lobe. However, this is often temporary as the hippocampus shares information via commissural fibres to the other temporal lobe. Bilateral lesion is required for permanent damage to memory.
Describe the journey of the Anterior Cerebral Artery and describe the consequences of lesions on particular cortical regions
The ACA lies on the medial surface of the hemispheres. The ACA follows the corpus callosum superiorly as the pericallosal artery and terminates at the area of the parieto-occipital fissure. The ACA supplies the medial part of:
- Prefrontal cortex - This is associated with working memory, planning, logic, reasoning, personality. Lesions may cause apathy, disinhibition, lack of drive, attention and indifference to things. This may be due to the effects on the dopamine connections between the Prefrontal cortex and limbic structures. Therefore there may be a lack of planning ahead alongside lack of drive orientated behaviour.
- Supplementary motor area - Apraxia.
- Paracentral lobule - Paralysis and sensory loss of contralateral lower limb with sparing of the upper limb. Incontinence due to defective control of perineal musculature and lack of sensory feedback from the bladder.
- Association sensory cortex - Minor agnosia. Minor because it only affects the medial surface of the ASC.
Describe the journey of the Middle Cerebral Artery and describe the consequences of lesions on particular cortical regions
The MCA branches laterally to exit the brain via the lateral fissure and supplies 2/3 of the outer surface of the brain. The MCA supplies via its branches:
- The Internal Capsule - symptoms of ‘classic stroke’ due to lateral striate arteries that supply the genu and posterior limb of the IC. As a result there is contralateral hemiplegia or lower facial paralysis due to supranuclear V lesion. Also, problems with sensation on contralateral side due to thalamocortical fibres being lesioned.
- Primary motor and sensory cortex - Paralysis of upper limb and neck
- Association sensory cortex - Agnosia
- Broca and Wernicke’s areas - Global aphasia if on dominant side (left). Contralateral hemi neglect if on non-dominant side (right)
- Primary auditory cortex - Normally no symptoms as there is bilateral innervation of auditory cortex from the organ of corti. As with memory, there must be a bilateral lesion to cause a permanent auditory pathology.
- Geniculocalcerine tract - Visual deficit. The MCA has 2 stems that supply the optic radiation.
Describe the journey of the Posterior Cerebral Artery and describe the consequences of lesions on particular cortical regions
The PCA is a continuation of the posterior communicating artery. The PCA supplies the inferior aspect of the brain and runs deep to the cerebellum. The regions it supplies includes the:
- Occipital lobe - A lesion to the primary visual cortex may cause cortical blindness. A lesion to the visual association area may cause agnosia. This can be especially distressing as this may cause an inability to recognise loved ones. A lesion to the optic radiations will cause contralateral homonymous hemianopia.
- Midbrain - Webber’s syndrome (alternating hemianopia). Ipsilateral III nuclei deficit with contralateral corticospinal tract dysfunction. The eye will be in the down and out position due to the unopposed action of the SO and LR muscles. Ptosis due to the lack of the levator palpebrae superioris. Pupil dilation due to uncontrolled sympathetics as there is no parasympathetics (no Edinger Westphal nucleus function)
- Thalamus - There may be thalamic pain syndrome whereby there is relaying of prioritised pain signals from the VPL and VPM to the cortex.
