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Large Vessel Stroke
in the Posterior Circulation |
A stroke may result from occlusion of a vessel in the
anterior or posterior circulation of the brain with
varying clinical manifestations. This learning objective
first defines the arterial vessels that comprise the
posterior circulation of the brain. It then reviews the
clinical manifestations of stroke resulting from
occlusion of each of its vessels. It is important to
contrast these clinical manifestations with those
involving strokes of the anterior circulation, as the
etiology and treatment may differ. For this information,
please refer to the previous learning objective,
large vessel strokes of the
anterior
circulation.
Approximately 20% of ischemic strokes occur in the
posterior circulation. A large vessel stroke of the
posterior circulation occurs when either
vertebral artery, the
basilar artery, or
the posterior cerebral arteries
(PCA) are blocked. Less commonly, the smaller branches
of the vertebral and basilar artery including the
posterior inferior cerebellar
(PICA), anterior inferior
cerebellar (AICA) and
superior cerebellar arteries
(SCA) can be infarcted. Most common among them is the
PICA which supplies the lateral medulla and inferior
cerebellum. The resulting clinical manifestations,
depend on the vascular territory supplied by the blocked
artery, as well as the degree of collateral vessels
helping to perfuse the given area of brain.
The vertebral arteries originate from the subclavian
arteries. They ascend through the foramen transversaria
in the vertebral bodies. They then wrap C2, then ascend
through the foramen magnum. The PICAs are then given off
which supply the dorsolateral medulla and inferior
cerebellum. The anterior spinal arteries also originate
from the vertebral arteries. The two vertebral arteries
then join to form the basilar artery at the
ponto-medullary junction. The basilar artery gives off
numerous small branches that supply the pons and
cerebellum. Two large branches, the SCA and AICA
originate from the superior and mid-basilar,
respectively. The PCAs are formed as a result of the
bifurcation of the distal basilar artery and supply the
midbrain, thalamus, medial aspect of the temporal lobe,
and occipital lobe. Please review the vasculature of the
posterior circulation in the diagrams below.
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Medial View
of the Brain |
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Lateral View
of the Brain |
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MRA of the Aortic Arch with Contrast Bolus.
(1) Aortic arch; (2) Brachiocephalic artery; (3) Right
Subclavian artery; (4) Left Subclavian artery; (5) Left
Common Carotid artery; (6) Right Common Carotid artery;
(7) Left Vertebral artery; (8) Left Common Carotid
artery; (9) Left Carotid Bifurcation; (10) Right
Vertebral artery; (11) Right Carotid Bifurcation; (12)
Right Internal Carotid artery; (13) Left Internal
Carotid Artery; (14) Left External Carotid artery; (15)
Right External Carotid artery; (16) Basilar artery; (17)
Right Internal Carotid artery (intracranial); (18) Left
Internal Carotid artery (intracranial); (19) Top of the
Basilar artery; (20) Vertebral arteries; (21) Vertebral
arteries
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MRA of the Neck - Extracranial Large Vessels.
ECA - External Carotid Artery; ICA - Internal Carotid
Artery; CCA - Common Carotid Artery; Vert - Vertebral
Artery
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Magnetic Resonance Angiography (MRA) Intracranial
Study. ACA - anterior cerebral artery; MCA - middle
cerebral artery; PCA - posterior cerebral artery; SCA -
superior cerebellar artery; AICA - anterior inferior
cerebellar artery; PICA - posterior inferior cerebellar
artery
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Anatomy of the Posterior Circulation: PCA - posterior cerebral artery; SCA -
superior cerebellar artery; AICA - anterior inferior
cerebellar artery; PICA - posterior inferior cerebellar
artery: ASA - anterior spinal artery
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The next part of this learning objective will review the
major clinical manifestations of different types of
large vessel anterior circulation including the
anterior cerebral,
middle cerebral and
internal carotid
arteries.
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Figure above: Vertebral artery angiogram, lateral
view. There is a smooth conical tapered occlusion of the
distal vertebral artery typical of a dissection. |
Vertebral Artery
Stroke |
The vertebral arteries and their distal branches provide
the main blood flow to the brainstem, cerebellum and
occipital lobes. A stroke involving one vertebral artery
may not be symptomatic due to the collateral
contribution from the other vertebral, or may be
catastrophic if the other vertebral is absent or
hypoplastic. The vertebral artery is also important as
the PICA, a branch of the vertebral supplies the
posterior inferior cerebellum and lateral medulla.
Incidence:
Relatively uncommon
Etiologies:
Intrinsic atherosclerosis. The most common locations are
at the
origin from the subclavian
and the
intracranial vertebral.
Embolic source from heart or aorta
Dissection |
Major Signs/Symptoms:
If other vertebral is
patent, may be asymptomatic, or only have symptoms
referable to the ipsilateral PICA, a branch of the
vertebral artery. This syndrome is known as the
Wallenberg or “lateral medullary” syndrome, and may
include the following signs and symptoms:
Vertigo, nausea, vomiting
Ipsilateral limb ataxia (dysmetria, dysdiadochokinesia)
Gait
ataxia
Nystagmus
Ipsilateral Horner’s syndrome due to disruption of
sympathetic tract: ptosis (droopy eyelid), miosis
(constricted pupil), hemianhidrosis (loss of sweating)
Loss of
pain and temperature in the ipsilateral face and
contralateral body (lateral spinothalalmic tract)
Ipsilateral weakness of the palate, pharynx and vocal
cords resulting in dysphagia, dysarthria and dysphonia
Loss of
gag reflex
If the
opposite vertebral is absent and there is absent
collateral blood flow to the brainstem or cerebellum,
the result may be catastrophic. Please refer to next
section on basilar artery stroke for explanation.
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Basilar Artery Stroke |
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The clinical manifestations of basilar artery stroke
vary depending on the degree of occlusion of the vessel,
the location of occlusion and the extent of collateral
flow. It is not infrequent to have prodromal TIA
symptoms, as the mechanism of basilar artery stroke is
frequently intrinsic atherosclerotic disease. For a list
of TIA symptoms of the vertebrobasilar circulation
including basilar artery, please click on the link for
learning objective “Significance
of a TIA and Differential of a Brief Neurological Spell.” |
Incidence: Uncommon
Etiologies:
Intrinsic atherosclerotic disease with thrombosis (more
likely if proximal or
mid-basilar)
Embolic
source (more likely if distal basilar)
Extension of vertebral dissection
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Major Signs/Symptoms:
If a basilar artery
stroke occurs, the symptoms may range from mild to
catastrophic. In the basis of the pons is affected
leaving the tegmentum intact, the “locked-in” syndrome
may occur with the following signs:
Tetraplegia (all four limbs, face and bulbar muscles)
Intact level of consciousness and sleep-wake cycles
Impairment of horizontal eye movements
Vertical eye movements and blinking spared
Bilateral babinski signs
Thus,
the patient has relatively intact perception of the
environment, but is unable to communicate except with
blinking or vertical eye movements. These deficits occur
due to massive infarction of the brainstem including
basis pontis (ventral pons) which results in disruption
of the corticobulbar and corticospinal tract fibers. The
wakefulness of the patient are intact due to sparing of
the reticular activating system in the tegmentum. The
vertical eye movement and blinking are intact due to
sparing of the dorsal midbrain supranuclear ocular
pathways.
In the case the tegmentum is also affected, the
patient will be in coma [from involvement of the
ascending reticular activating system (ARAS)]
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There
may also be signs and symptoms referable to the distal
branches of the basilar artery resulting in lateral
midbrain, thalamic, occipital and medial temporal lobe
infarction:
Memory
impairment (medial temporal lobe)
Loss of
sensation (thalamus)
Visual
loss (occipital lobe)
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Posterior Cerebral
Artery |
Patients with a stroke of the PCA usually present with
visual complaints, however depending on whether the PCA
is occluded proximally or distally, and whether
occlusion is unilateral or bilateral will determine the
clinical manifestations.
Incidence:
Common
Etiologies:
Embolic
source (proximal vertebral, aorta or heart)
Rarely,
intracranial artherosclerosis
Major Signs/Symptoms:
Single
PCA infarction:
Homonymous visual field defect
Scintillations at the edge of hemianopic field
Visual perseverations
Absence
of visual neglect (e.g., if a patient is given something
to read they will usually read the entire sentence,
whereas with right parietal stroke they will ignore the
contralateral side
Less Common:
Memory
disturbance
Peduncular hallucinosis (visual hallucinations of
brightly colored scenes and objects).
Hemiballismus, with subthalamic nucleus involvement
Hemiplegia, with cerebral peduncle involvement
3rd
nerve palsy, with midbrain involvement
Alexia
without agraphia (dominant lesion)
Transcortical sensory aphasia
Gerstmann's syndrome (R/L disorientation, finger anomia,
acalculia, agraphia, constructional apraxia)
Bilateral PCA Infarction:
Anton’s syndrome (cortical blindness with denial of
symptoms)
The
patient may confabulate visual perception
Balint’s syndrome [asimultagnosia (inability to see the
whole of an object); optic ataxia (inability to visually
guide a hand to its target); gaze apraxia (inability to
focus on a desired target)
Proximal PCA Infarction:
If the
very
proximal PCA is infarcted,
the small perforators to the thalamus and cerebral
peduncle may be affected, resulting in hemi- or
quadriplegia, and a depressed state of consciousness
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Posterior Inferior
Cerebellar Artery
(PICA) |
The PICA is the largest branch originating from the
vertebral artery. It wraps around the medulla,
supplying the lateral medulla before supplying the
inferior cerebellum. Infarction the lateral medulla
results in the Wallenberg's
syndrome, a classic neurologic condition
(scan above).
Incidence:
Relatively uncommon
Etiologies:
Same as the vertebral artery:
Intrinsic atherosclerosis. The most common locations are
at the origin from the subclavian and the intracranial
vertebral.
Embolic
source from heart or aorta
Dissection
Major Signs/Symptoms:
Vertigo, nausea, vomiting
Ipsilateral limb ataxia (dysmetria, dysdiadochokinesia)
Gait
ataxia
Nystagmus
Ipsilateral Horner’s syndrome due to disruption of
sympathetic tract: ptosis (droopy eyelid), miosis
(constricted pupil), hemianhidrosis (loss of sweating)
Loss of
pain and temperature in the ipsilateral face and
contralateral body (lateral spinothalalmic tract)
Ipsilateral weakness of the palate, pharynx and vocal
cords resulting in dysphagia, dysarthria and dysphonia
Loss of
gag reflex
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Note: Infarctions of the PICA are sometimes confused
clinically with gastroenteritis, because of the
prominent nausea and vomiting, especially if a
neurologic exam in not performed. If the entire
territory of the PICA is affected, infarction of the
inferior cerebellum may result in swelling and secondary
compression of nearby structures, including the fourth
ventricles and brainstem (see below). |
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If the swelling obstructs the 4th ventricle, acute
hydrocephalus can result. If not treated, it can lead to
transtentorial herniation and death
(see scan below) |
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