Vertebral Artery Atherothrombosis Workup

Updated: Jun 23, 2021
  • Author: Mark D Morasch, MD, RPVI; Chief Editor: Brian H Kopell, MD  more...
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Workup

Imaging Studies

A precise diagnosis of vertebrobasilar ischemia begins with an accurate assessment of the presenting symptom complex. This must be followed by efforts to exclude other causes for patient symptoms. These other medical conditions include inappropriate use of antihypertensive medications, cardiac arrhythmias, anemia, brain tumors, and benign vertiginous states. A thorough investigation generally includes a workup for inner-ear pathology and ruling out cardiac arrhythmias, internal carotid artery stenosis/occlusion, and the inappropriate use of medications.

Any systemic mechanism that decreases the mean pressure of the basilar artery may be responsible for hemodynamic symptomatology. Affected individuals may or may not have concomitant vertebral artery stenosis or occlusion. Certain prescription medications can mimic vertebrobasilar ischemia; as such, patient medications require a thorough review. Excessive use of antihypertensive medications is the most common cause of posterior circulation symptoms and can also cause hemodynamic posterior circulation ischemia by decreasing the perfusion pressure and inducing severe orthostatic hypotension.

The evaluation of patients with posterior circulation ischemia should include numerous specific steps. The precise circumstances associated with development of symptoms should be ascertained. Symptoms often appear on standing in older individuals with poor sympathetic control of their venous tone, which causes excessive pooling of blood in the veins of the leg. This is particularly common in patients with diabetes who have diminished sympathetic venoconstrictor reflexes. A 20 mm Hg systolic pressure drop on rapid standing is the criterion for a diagnosis of orthostatic hypotension causing low-flow in the vertebrobasilar system. In such cases, the pressure drop triggers the symptoms of posterior circulation ischemia.

A cardiac abnormality is another common cause of brainstem ischemia, especially in the elderly, and thorough evaluation should include monitoring for arrhythmias and a thorough assessment heart valve function. An ambulatory 24-hour electrocardiogram (Holter monitor) should be performed in patients with hemodynamic ischemia because arrhythmias are a common cause of symptomatology due to decreased cardiac output associated with the arrhythmia. Patients with ischemia secondary to arrhythmias often report the association of palpitations with the appearance of symptoms. Echocardiography is useful to rule out significant valvular pathology that could cause brainstem hypoperfusion.

Investigation must be undertaken to exclude inner-ear pathology, including rare cerebellar-pontine angle tumors. In addition, neurologic evaluation should be considered to rule out benign vertiginous states.

Because patients often present with a combination of cerebral hemispheric and posterior symptoms, investigation of the great vessels and the carotid circulation is usually warranted. An important aspect of the history is identifying triggering events such as positional or postural changes. This is followed by a thorough physical examination, which includes palpation, auscultation, pulse exam, and comparative arm blood pressures (recumbent and standing).

Physical examination can alert the physician to the possibility of a subclavian steal in patients with brachial pressure differences greater than 25 mm Hg or with diminished or absent pulses in one arm. The diagnosis of reversal of vertebral artery flow can be made accurately by noninvasive indirect methods and demonstrated directly by duplex imaging of the reversal of flow in the vertebral artery.

Patients may relate their symptoms to turning or extending their heads. Frequently, the mechanism is extrinsic compression of the vertebral artery, usually the dominant or the only one, by arthritic bone spurs. [7] To differentiate this mechanism from dizziness or vertigo secondary to labyrinthine disorders that appear with head or body rotation, the patient should attempt to reproduce the symptoms by turning the head slowly and then repeating the maneuver, but this time briskly, as when shaking the head from side to side. In labyrinthine disease, the sudden inertial changes caused by the latter maneuver result in immediate symptoms and nystagmus. Conversely, in extrinsic vertebral artery compression, a short delay occurs before the patient fears for his or her balance.

Once a suspicion of vertebrobasilar ischemia has been entertained, only a few studies clearly ascertain vertebral anatomy.

Ultrasonography

Duplex ultrasonography is an excellent tool for detecting lesions in the carotid artery, but it has significant limitations when used to detect vertebral artery pathology. Direct visualization of the second portion of the vessel is difficult because of its intraosseous course through the transverse processes of C2 to C6. The usefulness of duplex ultrasound lies in its ability to confirm reversal of flow within the vertebral arteries and detect flow velocity changes consistent with a proximal stenosis. In addition, this imaging may diagnose great vessel pathology and confirm subclavian steal. [17]

Zhang et al, in a study of the use of color Doppler ultrasound in 54 patients with intervertebral stenosis, found that color Doppler can reliably identify intervertebral stenosis and can be used as a preliminary reference for evaluating the condition. [19]

In a study of  218 cases of stenosis with vertebral artery origins in 139 patients, by Rice et al, ultrasound showed a sensitivity of 85.7%  and specificity of 99.5%for occlusion.  A mean flow velocity (MFV) cutoff value of 44 cm/s corresponded to 77% sensitivity and 70% specificity to detect vertebral artery origin stenosis >50%, and an MFV cutoff value of 60 cm/s corresponded with 70% sensitivity and 82% specificity to predict 70-99% stenosis. A peak systolic velocity (PSV) of 97 cm/s corresponded with a 72% sensitivity and 70% specificity to detect >50% stenosis, and a PSV cutoff value of 110 cm/s corresponded with 80% sensitivity and 72% specificity to predict 70-99% stenosis. [20]

MRI

Contrast-enhanced magnetic resonance angiography (MRA) with 3-dimensional (3D) reconstruction and maximum intensity projection (MIP) imaging techniques provide full imaging of the vessels, including the supra-aortic trunks, the carotid and vertebral arteries, and the circle of Willis. MRA does tend to "overcall" stenoses, especially those lesions found at the origin of the vertebral artery in the V1 segment. MRI allows for accurate and noninvasive visualization of the vertebral and basilar arteries, as well as the surrounding posterior fossa structures.

Brain stem infarctions are often missed by CT scan because they tend to be small and the resolution of the CT scan in the brain stem is poor. Transaxial MRI is also invaluable in detecting acute and chronic posterior fossa infarcts, as depicted in the first image below. This has been enhanced by the development of MRA with 3D reconstructions and MIP imaging, as depicted in the second image below.

Magnified view of MRI of the brain. The arrow deno Magnified view of MRI of the brain. The arrow denotes the site of a posterior fossa infarction.
Magnetic resonance angiography (MRA) with 3-dimens Magnetic resonance angiography (MRA) with 3-dimensional reconstruction of the extracranial and intracranial vertebral and carotid arterial system. The arrow denotes the right vertebral artery.

Arteriography

Selective subclavian and vertebral angiography remains the best test for preoperative evaluation of patients with vertebrobasilar ischemia. The most common site of disease, the vertebral artery origin, may not be well imaged with ultrasonography, MRA, or CT angiography, and catheter angiography may be necessary to prove pathology. Lesions at the origin of the vertebral artery, which are often the result of "spill-over" from the subclavian vessel, can, in some cases, only be displayed using oblique projections that are not part of standard arch evaluation.

Patients with suspected vertebral artery compression, usually by osteophytes, should undergo dynamic angiography, which incorporates provocative positioning. This is performed either with the patient sitting up, by means of bilateral brachial injections, or with the patient supine in the Trendelenburg position with the head resting against a block. In these positions, which exert axial compression of the cervical vertebrae, the angiographer should obtain the specific rotation or extension of the head that provokes the symptoms. When the patient is rendered symptomatic, the arteriographic injection demonstrates the extrinsic compression that developed with the head rotation or extension. [29]

Delayed imaging should be performed to demonstrate reconstitution of the extracranial vertebral arteries through cervical collaterals, such as the occipital artery or the thyrocervical trunk. [22] Because of this collateral network, the distal vertebral and basilar arteries usually remain patent despite a proximal vertebral artery occlusion. A patent V3 segment can be exploited as a distal target for reconstruction. (See the image below.)

Selective angiography of the left subclavian arter Selective angiography of the left subclavian artery demonstrating collateral flow to a patent distal left vertebral artery via the thyrocervical trunk.