2. • Arteries are:
the innominate and subclavian arteries in the
chest,
the vertebral arteries in the neck, and
the intracranial vertebral, basilar, and
posterior cerebral arteries.
3. SOURCE OF ISCHEMIA
• The most common causes of posterior circulation large artery ischemia are
atherosclerosis, embolism, and dissection.
• ●About one-third of posterior circulation strokes are caused by occlusive
disease within the large neck and intracranial arteries, which are the
vertebral arteries in the neck and the intracranial vertebral, basilar, and
posterior cerebral arteries.
• ●The proximal portion of the vertebral artery in the neck is the most
common location of atherosclerotic occlusive disease within the posterior
circulation . Atherosclerosis of the intracranial vertebral arteries and of the
basilar artery is also common.
• ●Dissection of the extracranial and intracranial vertebral arteries is
another frequent cause of ischemia within the posterior circulation.
• ●Unlike the vertebral and basilar arteries, atherosclerosis and dissection
of the posterior cerebral arteries is not common. Most infarcts in the
posterior cerebral artery territory are due to embolism from the heart,
aorta, or vertebral arteries.
4. SUBCLAVIAN AND INNOMINATE
ARTERIES
• Atherostenotic lesions of the innominate and subclavian
arteries do cause arm ischemia and transient ischemic
attacks (TIAs) but seldom cause strokes. Because the
vertebral arteries in the neck originate from the proximal
subclavian arteries, disease of the subclavian or innominate
arteries proximal to the vertebral artery origin can cause
reduction of vertebral artery flow.
• In the subclavian steal syndrome, obstruction of the
proximal subclavian artery produces a low-pressure system
within the ipsilateral vertebral artery and in blood vessels
of the ipsilateral upper extremity. Blood from a higher-
pressure system, the contralateral vertebral artery and
basilar artery, is diverted and flows retrograde downward
into the ipsilateral vertebral artery into the arm.
5. • Most often, subclavian artery disease is detected when patients
with coronary or peripheral vascular occlusive disease are referred
to ultrasound laboratories for noninvasive testing.
• Most patients with subclavian artery disease are asymptomatic. The
most frequent symptoms of subclavian artery disease relate to the
ipsilateral arm and hand. Coolness, weakness, and pain on use of
the arm are common.
• Neurologic symptoms are uncommon unless there is accompanying
carotid artery disease. Dizziness is by far the most common
neurologic symptom of the subclavian steal syndrome, and usually
has a spinning or vertiginous character. Diplopia, decreased vision,
oscillopsia, and staggering all occur, but less frequently, often
accompanying the dizziness. Attacks are brief and occasionally are
brought on by exercising the ischemic arm. However, in most
patients exercise of the ischemic limb does not provoke neurologic
symptoms or signs.
6. • Innominate artery disease is much less common than subclavian
artery disease [1,3,6]. When the innominate artery becomes
stenotic or occluded, signs and symptoms of decreased carotid
artery flow may also develop. Ipsilateral monocular visual loss,
ipsilateral cerebral hemisphere ischemia in the territories of the
anterior and middle cerebral arteries, ipsilateral arm ischemia, and
ischemic symptoms referable to the distal portion of the posterior
circulation and/or the cerebellum may be due to innominate artery
disease.
• Takayasu's disease and giant cell (temporal) arteritis can cause
subclavian and innominate artery occlusive disease. Young women
who smoke cigarettes and take oral contraceptives may develop
occlusive disease of the aortic arch vessels that mimics Takayasu
disease, except that it is not inflammatory.
7. EXTRACRANIAL VERTEBRAL ARTERIES
• The vast majority of occlusive lesions of the proximal vertebral arteries are
atherosclerotic. Among a series of 100 patients with angiographically
documented vertebral artery lesions, 92 percent were atherosclerotic in
origin [7]. The most common location of atherosclerotic occlusive disease
within the posterior circulation is the proximal portion of the vertebral
artery in the neck [1-5]. Atherosclerotic plaques may begin in the
subclavian artery and extend into the ostia of the proximal extracranial
vertebral arteries (ECVAs), or begin within the most proximal portion of
the ECVAs. Occlusions most often occur within the first inch (2 to 3 cm) of
the ECVAs. In contrast, atherosclerotic disease rarely involves the more
distal ECVAs within the cervical spine or near the penetration of the
arteries into the skull (figure 1).
• Another common cause of posterior circulation stroke is arterial
dissection, which usually involves the ECVA just before it enters the
foramen transversarium at C5 or C6, or in the very distal part of the artery
in the neck before it penetrates the dura mater to enter the cranial cavity.
9. • CT angiography can show occlusive lesions at the origin of the vertebral arteries
from the subclavian arteries as well as dissections. MR angiography often does not
show the origins of the vertebral arteries well.
• Proximal vertebral artery disease can cause sudden-onset strokes or transient
ischemic attacks (TIAs). The most frequently reported symptom during TIAs is
dizziness. These vertebral artery TIAs are indistinguishable from those described
by patients with subclavian steal, except that vertebral artery TIAs are not
precipitated by effort or by arm exertion.
• Although dizziness is the most common symptom, it is seldom the only neurologic
symptom. Usually, in at least some attacks, dizziness is accompanied by other signs
of hindbrain ischemia. Diplopia, oscillopsia, weakness of both legs, hemiparesis,
and numbness are often reported.
• In patients with proximal ECVA disease, a bruit can often be heard over the
supraclavicular region when auscultation is performed by moving the stethoscope
bell over the posterior cervical muscles and the mastoid. Sometimes a bruit may
be heard over the vertebral artery contralateral to the side of the stenotic
vertebral artery because of increased collateral blood flow.
10. • Artery to artery embolism and low flow — Embolization of white platelet-fibrin and red erythrocyte-fibrin thrombi
from atherostenotic occlusive lesions is the most common presentation of ECVA origin disease [1-5,8]. The
intraarterial emboli travel from the ECVA origin to reach the ipsilateral intracranial vertebral artery (ICVA), and
sometimes travel on to block the rostral basilar artery and/or its branches. In support of this observation, patients
presenting with ischemia in the distribution of the ICVA (the medulla and posterior inferior cerebellum) or the
distal basilar artery (superior cerebellum, occipital and temporal lobes in the territory of the posterior cerebral
arteries, or the thalamus or midbrain) show a high frequency of recent ECVA occlusions [1,3-5].
• A situation analogous to that of ECVA origin disease is well known in the anterior circulation, where
atherosclerotic disease of the internal carotid artery origin can cause distal ischemia by artery to artery
embolization. As an example, it is not uncommon that a patient with a small, middle cerebral artery territory
infarct is found to have an occlusion at the internal carotid artery origin by ultrasound or angiography. In most of
these cases, it is likely that a recently formed occlusive thrombus in the internal carotid artery fragmented and
embolized distally, causing the middle cerebral artery territory stroke.
• In patients with proximal ECVA stenosis, intraarterial (artery to artery) embolism is a much more frequent cause of
ischemia to the intracranial posterior circulation arteries than hemodynamic insufficiency (ie, low flow). This point
is illustrated by results from the New England Medical Center Posterior Circulation Registry, which evaluated a
series of 407 patients who had posterior circulation TIAs or strokes within the prior six months and included 80
patients with severe stenosis or occlusion of the proximal ECVA [1]. In 45 (56 percent) of these 80 patients,
embolization from the vertebral artery lesion was the most likely cause of brain ischemia [1]. Only 13 patients (16
percent) had hemodynamic-related TIAs, and 12 of these 13 had severe bilateral vertebral artery occlusive
disease. The only patient with unilateral vertebral artery disease had bilateral internal carotid artery occlusions.
11. • Dissection and other causes — Dissection of the ECVA usually involves the distal portion of the ECVA as it winds
around the upper cervical vertebrae [9]. Sometimes dissections involve the proximal ECVA between the origin of
the artery and its entry into the vertebral column, usually at C5 or C6. Pain in the neck and/or occiput and TIAs or
strokes involving the lateral medulla and cerebellum are the most common findings. (See "Spontaneous cerebral
and cervical artery dissection: Clinical features and diagnosis", section on 'Clinical features'.)
• Ischemic symptoms due to ECVA dissection are most often vestibulocerebellar and include dizziness, vertigo,
veering to one side, and loss of balance. When infarcts develop, they usually involve the inferior portion of the
cerebellum, causing gait ataxia. Less common, are emboli to the distal posterior circulation, especially the
posterior cerebral artery territories, causing a hemianopia. Occasionally cervical root pain and signs, and spinal
cord ischemia can develop.
• In older patients, giant cell arteritis is an occasional cause of occlusive disease involving the distal extracranial
vertebral artery just before it penetrates the dura to become intracranial. (See "Clinical manifestations of giant cell
(temporal) arteritis".)
• Rotational vertebral artery occlusion is an uncommon cause of transient posterior circulation ischemic symptoms,
mainly paroxysmal vertigo or nonspecific dizziness, which may be accompanied by nystagmus, tinnitus, syncope,
blurred vision, nausea, or vomiting [10,11]. The nystagmus typically has a prominent downbeat component, but
may also include torsional and horizontal components [12]. The symptoms are due to dynamic compression of one
(dominant) vertebral artery by bony elements of the cervical spine, triggered by head turning to one side, or less
often by head turning to both sides or head tilting [10,11]. In most reported cases, there is associated hypoplasia
or stenosis of the other vertebral artery. The symptoms are relieved by returning the head to the neutral position.
Few if any cases result in infarction with permanent neurologic deficits from this mechanism.
12. INTRACRANIAL VERTEBRAL
ARTERIES —
• Atherostenotic disease can involve any portion of the intracranial vertebral arteries (ICVA) (figure
2). The most common location of ICVA stenosis is the distal portion of the artery at or near the
vertebral-basilar artery junction. Another common site of ICVA stenosis is the proximal portion of
the vertebral artery just after dural penetration and before giving off the posterior inferior
cerebellar artery (PICA) branch. Dissection of the ICVA also occurs, and ischemic symptoms are
usually accompanied by prominent headache [13]. ICVA dissections often extend into the basilar
artery.
• Occlusive ICVA disease presents in a variety of different ways [4,14,15]:
• ●Asymptomatic occlusion
• ●Transient ischemic attacks (TIAs), usually including vestibulocerebellar symptoms or elements of
the lateral medullary syndrome
• ●Lateral medullary infarcts
• ●Medial medullary infarction
• ●Infarction of one-half of the medulla (hemimedullary infarction) including the lateral and medial
medulla on one side
• ●Cerebellar infarction in PICA territory
• ●Embolization of the ICVA thrombus to the distal basilar artery and its branches causing TIAs
and/or strokes
• ●Propagation of the ICVA thrombus into the basilar artery causing a basilar artery syndrome
14. • Lateral medullary infarction — Lateral
medullary infarction (Wallenberg syndrome) is
the most common and important syndrome
related to intracranial vertebral artery
occlusion (figure 3) [4,15]. The diagnosis is
often missed by non-neurologists, and so the
features are very important to know and
understand.
