Vertebral artery dissection is a dissection of the inner lining of the
vertebral artery, which is located in the neck and supplies blood to the
brain. After the tear, blood enters the arterial wall and forms a blood clot,
thickening the artery wall and often impeding blood flow. The symptoms of
vertebral artery dissection include head and neck pain and intermittent or
permanent stroke symptoms such as difficulty speaking, impaired
coordination and visual loss. It is usually diagnosed with a
contrast-enhanced CT or MRI scan. Vertebral dissection may occur after
physical trauma to the neck, such as a blunt injury, strangulation or
manipulation, but may also happen spontaneously. 1–4% of spontaneous cases
have a clear underlying connective tissue disorder affecting the blood
vessels. Treatment is usually with either antiplatelet drugs such as
aspirin or with anticoagulants such as heparin or warfarin.
Vertebral artery dissection is less common than carotid artery dissection.
The two conditions combined account for 10–25% of non-hemorrhagic strokes in
young and middle-aged people. Over 75% recover completely or with minimal
impact on functioning, with the remainder having more severe disability
and a very small proportion dying from complications. It was first described in
the 1970s by the Canadian neurologist C. Miller Fisher.
Classification Vertebral artery dissection is one of
the two types of dissection of the arteries in the neck. The other type,
carotid artery dissection, involves the carotid arteries. Vertebral artery
dissection is further classified as being either traumatic or spontaneous,
and it may also be classified by the part of the artery involved:
extracranial and intracranial. Signs and symptoms
Head pain occurs in 50–75% of all cases of vertebral artery dissection. It tends
to be located at the back of the head, either on the affected side or in the
middle, and develops gradually. It is either dull or pressure-like in
character or throbbing. About half of those with VAD consider the headache
distinct, while the remainder have had a similar headache before. It is suspected
that VAD with headache as the only symptom is fairly common; 8% of all
cases of vertebral and carotid dissection are diagnosed on the basis of
pain alone. Obstruction of blood flow through the
affected vessel may lead to dysfunction of part of the brain supplied by the
artery. This happens in 77–96% of cases. This may be temporary in 10–16% of
cases, but many end up with a permanent deficit or a stroke. The vertebral
artery supplies the part of the brain that lies in the posterior fossa of the
skull, and this type of stroke is therefore called a posterior circulation
infarct. Problems may include difficulty speaking or swallowing; this occurs in
less than a fifth of cases and occurs due to dysfunction of the brainstem.
Others may experience unsteadiness or lack of coordination due to involvement
of the cerebellum, and still others may develop visual loss due to involvement
of the visual cortex in the occipital lobe. In the event of involvement of the
sympathetic tracts in the brainstem, a partial Horner's syndrome may develop;
this is the combination of a drooping eyelid, constricted pupil, and an
apparently sunken eye on one side of the face.
If the dissection of the artery extends to the part of the artery that lies
inside the skull, subarachnoid hemorrhage may occur. This arises due to
rupture of the artery and accumulation of blood in the subarachnoid space. It
may be characterized by a different, usually severe headache; it may also
cause a range of additional neurological symptoms.
13–16% of all people with vertebral or carotid dissection have dissection in
another cervical artery. It is therefore possible for the symptoms to occur on
both sides, or for symptoms of carotid artery dissection to occur at the same
time as those of vertebral artery dissection. Some give a figure of
multiple vessel dissection as high as 30%.
Causes The causes of vertebral artery
dissection can be grouped under two main categories, spontaneous and traumatic.
= Spontaneous= Spontaneous cases are considered to be
caused by intrinsic factors that weaken the arterial wall. Only a very small
proportion have a clear underlying connective tissue disorder, such as
Ehlers–Danlos syndrome type 4 and more rarely Marfan's syndrome. Ehlers-Danlos
syndrome type 4, caused by mutations of the COL3A gene, leads to defective
production of the collagen, type III, alpha 1 protein and causes skin
fragility as well as weakness of the walls of arteries and internal organs.
Marfan's syndrome results from mutations in the FBN1 gene, defective production
of the protein fibrillin-1, and a number of physical abnormalities including
aneurysm of the aortic root. There have also been reports in other
genetic conditions, such as osteogenesis imperfecta type 1, autosomal dominant
polycystic kidney disease and pseudoxanthoma elasticum, α1 antitrypsin
deficiency and hereditary hemochromatosis, but evidence for these
associations is weaker. Genetic studies in other connective tissue-related genes
have mostly yielded negative results. Other abnormalities to the blood
vessels, such as fibromuscular dysplasia, have been reported in a
proportion of cases. Atherosclerosis does not appear to increase the risk.
There have been numerous reports of associated risk factors for vertebral
artery dissection; many of these reports suffer from methodological weaknesses,
such as selection bias. Elevated homocysteine levels, often due to
mutations in the MTHFR gene, appear to increase the risk of vertebral artery
dissection. People with an aneurysm of the aortic root and people with a
history of migraine may be predisposed to vertebral artery dissection.
= Traumatic= Traumatic vertebral dissection may
follow blunt trauma to the neck, such as in a traffic collision, direct blow to
the neck, strangulation, or whiplash injury. 1–2% of those with major trauma
may have an injury to the carotid or vertebral arteries. In many cases of
vertebral dissection, people report recent very mild trauma to the neck or
sudden neck movements, e.g. in the context of playing sports. Others report
a recent infection, particularly respiratory tract infections associated
with coughing. Trauma has been reported to have occurred within a month of
dissection in 40% with nearly 90% of this time the trauma being minor. It has
been difficult to prove the association with mild trauma and infections
statistically. It is likely that many "spontaneous" cases may in fact have
been caused by such relatively minor insults in someone predisposed by other
structural problems to the vessels. Vertebral artery dissection has also
been reported in association with some forms of neck manipulation. There is
significant controversy about the level of risk of stroke from neck
manipulation. It has been suggested that the relationship is causative, but this
is disputed by some chiropractic proponents of this treatment modality,
who believe that the dissection is probably already present before people
seek treatment. At this time, conclusive evidence does not exist to support
either a strong association between neck manipulation and stroke, or no
association. Mechanism
The vertebral arteries arise from the subclavian artery, and run through the
transverse foramen of the upper six vertebrae of the neck. After exiting at
the level of the first cervical vertebra, its course changes from
vertical to horizontal, and then enters the skull through the foramen magnum.
Inside the skull, the arteries merge to form the basilar artery, which joins the
circle of Willis. In total, three quarters of the artery are outside the
skull; it has a high mobility in this area due to rotational movement in the
neck and is therefore vulnerable to trauma. Most dissections happen at the
level of the first and second vertebrae. The vertebral artery supplies a number
of vital structures in the posterior cranial fossa, such as the brainstem,
the cerebellum and the occipital lobes. The brainstem harbors a number of vital
functions and controls the nerves of the face and neck. The cerebellum is part of
the diffuse system that coordinates movement. Finally, the occipital lobes
participate in the sense of vision. Dissection occurs when blood accumulates
in the wall of the blood vessel. This is most likely due to a tear in the tunica
intima, allowing blood to enter the tunica media, although other lines of
evidence have suggested that the blood may instead arise from the vasa vasorum,
the small blood vessels that supply the outer layer of larger blood vessels.
Various theories exist as to whether people who sustain carotid and vertebral
artery dissection, even if not suffering from a connective tissue disorder, have
an underlying vulnerability. Biopsy samples of skin and other arteries has
indicated that this might be a possibility, but no genetic defect in
collagen or elastin genes has been convincingly proven. Other studies have
indicated inflammation of the blood vessels, as measured by highly sensitive
C-reactive protein in the blood. Once dissection has occurred, two
mechanisms contribute to the development of stroke symptoms. Firstly, the flow
through the blood vessel may be disrupted due to the accumulation of
blood under the vessel wall, leading to ischemia. Secondly, irregularities in
the vessel wall and turbulence increase the risk of thrombosis and embolism of
these clots of the brain. From various lines of evidence, it appears that
thrombosis and embolism is the predominant problem.
Subarachnoid hemorrage due to arterial rupture typically occurs if the
dissection extends into the V4 section of the artery. This may be explained by
the fact that the arterial wall is thinner and lacks a number of structural
supports in this section. Diagnosis
Various diagnostic modalities exist to demonstrate blood flow or absence
thereof in the vertebral arteries. The gold standard is cerebral angiography.
This involves puncture of a large artery and advancing an intravascular catheter
through the aorta towards the vertebral arteries. At that point, radiocontrast
is injected and its downstream flow captured on fluoroscopy. The vessel may
appear stenotic, occluded, or as an aneurysm. The narrowing may be described
as "rat's tail" or "string sign". Cerebral angiography is an invasive
procedure, and it requires large volumes of radiocontrast that can cause
complications such as kidney damage. Angiography also does not directly
demonstrate the blood in the vessel wall, as opposed to more modern
modalities. The only remaining use of angiography is when endovascular
treatment is contemplated. More modern methods involve computed
tomography and magnetic resonance imaging. They use smaller amounts of
contrast and are not invasive. CT angiography and MR angiography are more
or less equivalent when used to diagnose or exclude vertebral artery dissection.
CTA has the advantage of showing certain abnormalities earlier, tends to be
available outside office hours, and can be performed rapidly. When MR
angiography is used, the best results are achieved in the T1 setting using a
protocol known as "fat suppression". Doppler ultrasound is less useful as it
provides little information about the part of the artery close to the skull
base and in the vertebral foramina, and any abnormality detected on ultrasound
would still require confirmation with CT or MRI.
Treatment Treatment is focused on reducing stroke
episodes and damage from a distending artery. Four treatment modalities have
been reported in the treatment of vertebral artery dissection. The two
main treatments involve medication: anticoagulation and antiplatelet drugs.
More rarely, thrombolysis may be administered, and occasionally
obstruction may be treated with angioplasty and stenting. No randomized
controlled trials have been performed to compare the different treatment
modalities. Surgery is only used in exceptional cases.
= Anticoagulation and aspirin= From analysis of the existing small
treatment trials of cervical artery dissection it appears that aspirin and
anticoagulation are equally effective in reducing the risk of further stroke or
death. Anticoagulation is regarded as more powerful than antiplatelet therapy,
but anticoagulants may increase the size of the hematoma and worsen obstruction
of the affected artery. Anticoagulation may be relatively unsafe if a large
stroke has already occurred, as hemorrhagic transformation is relatively
common, and if the dissection extends into V4. Anticoagulation may be
appropriate if there is rapid blood flow on transcranial doppler despite the use
of aspirin, if there is a completely occluded vessel, if there are recurrent
stroke-like episodes, or if free-floating blood clot is visible on
scans. Warfarin is typically continued for 3–6 months, as during this time the
flow through the artery usually improves, and most strokes happen within
the first 6 months after the development of the dissection. Some regard 3 months
as sufficient. Professional guidelines in the UK
recommend that patients with VA dissection should be enrolled in a
clinical trial comparing aspirin and anticoagulation if possible. American
guidelines state that the benefit of anticoagulation is not currently
established. = Thrombolysis, stenting and surgery=
Thrombolysis, stenting and surgery are not used as widely as anticoagulation or
antiplatelet drugs. These treatments are invasive or more risky, and are
typically reserved for situations where symptoms worsen despite medical
treatment, or where medical treatment may be unsafe.
Thrombolysis is enzymatic destruction of blood clots. This is achieved by the
administration of a drug that activates plasmin, an enzyme that occurs naturally
in the body and digests clots when activated. Thrombolysis is an accepted
treatment for heart attacks and stroke unrelated to dissection. In cervical
artery dissection, only small case series are available. The thrombolytic
drug is administered either intravenously or during cerebral
angiography through a catheter directly into the affected artery. The data
indicates that thrombolysis is safe, but its place in the treatment of VAD is
uncertain. Stenting involves the catheterization of
the affected artery during angiography, and the insertion of a mesh-like tube;
this is known as "endovascular therapy". This may be performed to allow the blood
to flow through a severely narrowed vessel, or to seal off an aneurysm.
However, it is unclear whether the technical success of the procedure
translates into improved outcomes, as in both cases the problem often resolves
spontaneously over time. Stenting, as well as the insertion of coils by means
of angiography, may be performed if there is an aneurysm and/or extension of
the dissection into the V4 section of the artery.
Surgery carries a high risk of complications, and is typically only
offered in case of inexorable deterioration or contraindications to
any of the other treatments. Various arterial repair procedures have been
described. Prognosis
Prognosis of spontaneous cervical arterial dissection involves
neurological and arterial results. The overall functional prognosis of
individuals with stroke due to cervical artery dissection does not appear to
vary from that of young people with stroke due to other causes. The rate of
survival with good outcome is generally about 75%, or possibly slightly better
if antiplatelet drugs are used. In studies of anticoagulants and aspirin,
the combined mortality with either treatment is 1.8-2.1%.
After the initial episode, 2% may experience a further episode within the
first month. After this, there is a 1% annual risk of recurrence. Those with
high blood pressure and dissections in multiple arteries may have a higher risk
of recurrence. Further episodes of cervical artery dissection are more
common in those who are younger, have a family history of cervical artery
dissection, or have a diagnosis of Ehlers-Danlos syndrome or fibromuscular
dysplasia. Epidemiology
The annual incidence is about 1.1 per 100,000 annually in population studies
from the United States and France. From 1994 to 2003, the incidence increased
threefold; this has been attributed to the more widespread use of modern
imaging modalities rather than a true increase. Similarly, those living in
urban areas are more likely to receive appropriate investigations, accounting
for increased rates of diagnosis in those dwelling in cities. It is
suspected that a proportion of cases in people with mild symptoms remains
undiagnosed. There is controversy as to whether VAD
is more common in men or in women; an aggregate of all studies shows that it
is slightly higher incidence in men. Men are on average 37–44 years old at
diagnosis, and women 34–44. While dissection of the carotid and vertebral
arteries accounts for only 2% of strokes, they cause 10–25% of strokes in
young and middle-aged people. Dissecting aneurysms of the vertebral
artery constitute 4% of all cerebral aneurysms, and are hence a relatively
rare but important cause of subarachnoid hemorrhage.
History Spontaneous vertebral artery dissection
was described in the 1970s. Prior to this, there had been isolated case
reports about carotid dissection. In 1971, C. Miller Fisher, a Canadian
neurologist and stroke physician working at Massachusetts General Hospital, first
noted the "string sign" abnormality in carotid arteries on cerebral angiograms
of stroke patients, and subsequently discovered that the same abnormality
could occur in the vertebral arteries. He reported the discovery in a paper in
1978. Notable cases
Australian cricketer Phillip Hughes died on 27 November 2014 after developing a
vertebral artery dissection as a result of being struck on the side of the neck
by a cricket ball during a Sheffield Shield match on 25 November 2014. The
ball struck Hughes on the base of the skull just behind his left ear which
caused a vertebral artery dissection complicated by subarachnoid hemorrhage.
References External links
Cervical Artery Dissections and Ischemic Stroke Patients, international research
collaboration into cervical artery dissection