Cervical Carotid and Vertebral Disease
Reshma Narula, MD
Samit M. Shah, MD, PhD
Mamadou L. Sanogo, MD
Michele H. Johnson, MD, FACR, FASER
Key Points
Review imaging options for assessment of the cervical vasculature.
Recognize common pathologies that affect the cervical carotid and/or vertebral arteries.
Review the indications, risks, and benefits of carotid artery stenting and neuroprotection options.
I. Introduction
Imaging assessment of the extracranial carotid artery includes a variety of cross-sectional and catheter-based techniques with different advantages, disadvantages, risks, and benefits. Cost, the need for iodinated contrast, radiation dose, imaging-modality-related limitations, and contraindications must be considered. Familiarity with features of each imaging modality is important for confidently selecting the best modality for an individual patient and suspected disease process.
A. Ultrasound
1. Duplex ultrasound (DUS) of the cervical carotid arteries is the mainstay for noninvasive evaluation of carotid stenosis (Fig. 3.1).1
2. DUS is low-cost and readily accessible and provides both anatomic and flow velocity information that each reflect the hemodynamic degree of stenosis and morphological characteristics of atherosclerotic plaque.
3. DUS is less useful for evaluation of the vertebral arteries because of the intraosseous course of the vertebral arteries through the foramina transversarium.
Soft, friable plaque, calcified plaque, and ulcerated plaque each have characteristic appearances on anatomic ultrasound.
Flow velocities and wave tracings are helpful, in determining both the degree of stenosis and the degree of flow alteration in any given patient.
FIGURE 3.1: Carotid Ultrasound (DUS). A, Normal carotid bulb. B, Normal proximal internal carotid artery (ICA). C-E, Left carotid stenosis. Transverse and sagittal DUS images at the carotid bifurcation demonstrate soft plaque within the ICA. F-H, Right carotid bruit. DUS demonstrates the carotid bulb with calcified shadowing atherosclerotic plaque in the ICA. Peak systolic velocity at the bulb is 273 cm/s suggestive of >70% stenosis. Case courtesy of Dr. Gowthaman Gunabushanam.
4. DUS assessment can be limited when the patient has significant calcifications at the carotid bifurcation as well as in patients who are large in size with a “short neck” or in whom the carotid bifurcation is high—above the mandibular angle, making access to the carotid bifurcation difficult.
B. Computed Tomographic Angiography
1. Computed tomographic angiography (CTA) has become the primary cross-sectional imaging modality for suspected anatomic lesions of the extracranial carotid and vertebral arteries including clinical settings such as trauma, stable atherosclerosis, and stroke (Fig. 3.2).2
2. Ionizing radiation and iodinated contrast are both required.
3. Modern CT scanners acquire excellent images while minimizing contrast and radiation dosages.
Most commonly, conventional CTA includes static images performed in the arterial phase with filming of the head and neck with the same contrast bolus. In practice, reconstruction protocols vary, but generally include axial, coronal, sagittal, and oblique images with or without 3D volume rendered or vessel tracking imaging.
Application of dual energy techniques for CTA acquisition allows for automated bone removal and plaque characterization using the different energy spectrum for evaluation.3
Newer time-resolved or multiphasic CTA with rapid sequential imaging allows for visible depiction of flow within the vessel, analogous to digital subtraction angiography.4
4. CT perfusion techniques may be adjunctive in the assessment of the significance of carotid stenosis or the significance of an intracranial stenosis.5
C. Magnetic Resonance Angiography
1. Magnetic resonance angiography (MRA) time-of-flight imaging has the advantages of requiring no ionizing radiation and no intravenous contrast administration to obtain imaging of the carotid artery (Fig. 3.3).6
2. There are some patients who cannot undergo MRI or who may require special monitoring (ie, pacemakers or implanted cardioverter-defibrillators).
Metallic oral implants (including clips and dental hardware) may create significant imaging artifacts at the level of the carotid arteries, precluding adequate vessel evaluation.
3. Noncontrast time-of-flight MRA is an excellent screening tool for cervical or intracranial vascular disease but has the significant disadvantage that a high-grade stenosis may appear as an occlusion unless contrast MRA is employed.
4. Contrast MRA improves the visualization of a tiny residual vascular lumen, permitting accurate differentiation of high-grade stenosis versus occlusion.
FIGURE 3.2: Computed tomographic angiography (CTA). A, Sagittal CTA of normal carotid bifurcation. B, Axial CTA demonstrates the carotid bulb on the right and the internal and external carotid arteries on the left. C, Axial CTA through the upper cervical carotid arteries bilaterally. D, Sagittal CTA demonstrates high-grade calcific stenosis. E and F, Sequential axial CTA images illustrate mixed calcified and noncalcified plaque and the marked right internal carotid artery stenosis. G and H, CTA of the left carotid artery viewed in the inverted format demonstrates the calcific plaque as black and mild luminal irregularity without hemodynamically significant stenosis. The 3D volume rendered images with vessel tracking and axial segmentation are helpful for assessment of the character of the plaque and the degree of stenosis. I and J, In contrast, on the right, there is a long segment but lesser narrowing than on the left, and the plaque is composed of both calcified and noncalcified plaque, which may be more friable and carry higher risk of distal embolization. Plaque characterization as well as anatomic features of the target lesion will influence treatment decisions.
FIGURE 3.2 Cont’d
5. MRA predominantly images the lumen of the vessel; however, evaluation of source images may allow for plaque characterization, particularly when thin section high-resolution imaging algorithms are applied.
6. Time-resolved MRA techniques are also useful primarily for assessment of arteriovenous shunting and fistulous lesions. These are less commonly employed for cervical vascular disease.
FIGURE 3.3: Magnetic resonance angiography (MRA). A, Time-of-flight (TOF) noncontrast MRA demonstrates the vasculature, which is better resolved on the postcontrast MRA series (B). C and D, Carotid stenosis (arrow) is best evaluated on the postcontrast axial source image and the MIP (maximum intensity projection) reconstruction.
D. Digital Subtraction Angiography
1. Digital subtraction angiography (DSA) utilizes conventional x-ray with digital acquisition of images in rapid sequence during intra-arterial injection of contrast.
This provides high-resolution, time-resolved vascular imaging with both anatomic delineation and real-time physiologic depiction of flow dynamics (Fig. 3.4).
2. DSA is an invasive technique requiring catheter access usually via femoral, radial, or brachial routes, although direct carotid access may be employed in select cases.
3. Rotational digital acquisition permits creation of 3D volume rendered images. DSA remains the gold standard for DUS, CTA, and MRI/MRA.9
II. Cervical Carotid and Vertebral Disease
Evaluation of cervical extracranial vascular disease begins with the vessel origins from the aortic arch. The innominate artery arises from the aortic arch and divides into the right common carotid artery and the right subclavian artery, from which the right vertebral artery
arises. The left common carotid artery arises as the next branch from the arch and finally the left subclavian, which gives rise to the left vertebral artery. The common carotid arteries divide into internal and external carotid arteries in the mid cervical region usually between C2 and C6, and the level may vary from one side to the other. The vertebral arteries proceed
cranially, traversing the foramen transversarium of the cervical vertebra extending to the C2 level and around the arch of C1 until the arteries enter the dura at the foramen magnum and join to form the basilar artery superiorly10 (Fig. 3.5; Table 3.1).
arises. The left common carotid artery arises as the next branch from the arch and finally the left subclavian, which gives rise to the left vertebral artery. The common carotid arteries divide into internal and external carotid arteries in the mid cervical region usually between C2 and C6, and the level may vary from one side to the other. The vertebral arteries proceed
cranially, traversing the foramen transversarium of the cervical vertebra extending to the C2 level and around the arch of C1 until the arteries enter the dura at the foramen magnum and join to form the basilar artery superiorly10 (Fig. 3.5; Table 3.1).
 FIGURE 3.4: Digital subtraction angiography (DSA). A and B, AP oblique and lateral DSA of the common carotid artery demonstrate a normal configuration in this young adult patient. C and D, The cervical internal carotid artery may be tortuous with hairpin or 360° loops, which are easily appreciated on CTA but may be difficult to navigate when carotid stenting or intracranial intervention are contemplated. E, This 65-year-old patient presented with hand claudication and subclavian stenosis was demonstrated. F and G, DSA with injection of the right vertebral artery in the arterial and venous phases demonstrates retrograde flow in the left vertebral artery with faint filling of the subclavian artery—subclavian steal phenomenon. H, Following transfemoral left subclavian stent placement, the vertebral artery was preserved and antegrade flow restored. |
 FIGURE 3.4 Cont’d |
III. Atherosclerotic Disease
A. Causes of Ischemic Stroke
1. Extracranial carotid artery disease is one of the leading causes of ischemic stroke accounting for approximately 10% of all ischemic strokes.
2. Carotid artery revascularization in the setting of extracranial atherosclerotic disease, with either carotid endarterectomy (CEA) or carotid artery stenting (CAS), is now well-established treatment for symptomatic and asymptomatic carotid atherosclerotic disease in specific patients.11
3. As not every patient with extracranial carotid artery atherosclerotic disease carries the same risk of future stroke, key risk factors should be considered to determine which specific patients should be revascularized.
B. Risk Factors
1. Major risk factors include the degree of stenosis and characteristics of the plaque seen within the artery.
2. Other patient-specific characteristics include age, gender, and comorbid medical conditions.
FIGURE 3.5: Arch Anatomy. A, Normal arch configuration. B, More tortuous great vessels in this elderly patient may make interventions more challenging. Note the left vertebral artery arises directly from the aortic arch. C, A common origin of the innominate and left common carotid arteries may require a recurve catheter for navigation as in this case. D and E, This patient was scheduled for a right carotid stent; however, the hostile arch and the acute reverse curve of the internal carotid stenosis led the operator to abandon this approach for carotid endarterectomy.
TABLE 3.1. Aortic Arch Classification
Type I
Great vessels arising from the top of the arch
Type II
Great vessels arising between the parallel planes delineated by the outer and inner curves of the arch
Type III
Great vessels arising caudal to the inner surface of the arch or of the ascending aorta
C. Modality for Revascularization
1. The choice of modality for revascularization is based on a combination of these key risk factors and anatomic considerations.
2. We review recent trial evidence surrounding carotid revascularization in both symptomatic and asymptomatic carotid artery disease, and the data supporting patient selection for each modality.
3. A few definitions are important to know to understand and compare the trial data.
D. Defining Carotid Artery Stenosis
1. In the North American Symptomatic Carotid Endarterectomy Trial (NASCET), a uniform method for measurement of percentage carotid stenosis at angiography was defined by comparing the minimal residual lumen at the level of the stenotic lesion with the diameter of the more distal internal carotid artery at which the walls of the artery first become parallel (beyond any poststenotic dilatation).
2. The following formula is used: Degree of stenosis = (1−A/B) × 100%.
A is the diameter at the point of maximum stenosis and B is the diameter of the arterial segment distal to the stenosis where the walls first become parallel.12
This method of measurement has been adapted to CT angiography.
E. Symptomatic Versus Asymptomatic Extracranial Carotid Stenosis
1. Symptomatic extracranial carotid artery stenosis is defined as an atherosclerotic lesion of at least 50% stenosis proximal to the vascular territory that corresponds to the patient’s clinical symptomatology (stroke or transient ischemic attack) and/or the anatomic location of the infarct on imaging.
2. Atherosclerotic stenosis of the carotid artery may result in ischemic symptoms secondary to hypoperfusion or embolization.
3. Asymptomatic extracranial carotid artery stenosis is defined as an atherosclerotic lesion of at least 50% stenosis without clinical or imaging evidence of stroke.
4. Currently, it is recommended that best medical management should be implemented immediately in both symptomatic and asymptomatic atherosclerotic carotid disease whenever it is first discovered.14,15
Best medical management involves vascular risk factor modification and includes aggressive control of hypertension, hyperlipidemia, diabetes mellitus, smoking cessation, and initiation of an antiplatelet agent.16
 FIGURE 3.6: Digital subtraction angiography (DSA) and Computed tomographic angiography (CTA) with NASCET measurements. A, NASCET measurements on CTA minimal luminal diameter (black line) compared with the straight portion of the internal carotid artery beyond any poststenotic dilatation (white line). B, With heavy calcification (black arrow), absolute measurement in mm may be preferable. C and D, This patient had symptoms referable to reduced cerebral perfusion. Pre- and poststent cervical images demonstrate residual stenosis due to the heavy calcific plaque. E and F, Cerebral DSA pre- and poststent show remarkable improvement on perfusion on the right and his symptoms improved. |
IV. Revascularization in Extracranial Carotid Artery Stenosis
A. Evidence
1. There is substantial evidence to support revascularization for symptomatic extracranial carotid artery disease. Many large randomized trials including the European Carotid Surgery Trial (ECST), the NASCET, and the US Department of Veteran Affairs Cooperative Study Program (CSP) showed superiority of carotid endarterectomy with best medical management over best medical management alone for symptomatic, high-grade carotid artery stenosis.12,17,18
2. Patients included in these studies were those with greater than 70% carotid artery stenosis on angiography and who had ipsilateral ischemic strokes, monocular blindness, or symptoms of a transient ischemic attack.
3. A pooled analysis from these trials showed that the rate of 30-day stroke risk was lower in the surgical group compared with the medical group.
4. The NASCET study specifically showed that the number needed to treat with carotid endarterectomy was six for patients with symptomatic high-grade carotid artery stenosis.
5. The studies also showed that for patients with less than 50% stenosis of the carotid artery, surgery did not significantly lower the future stroke risk.
6. For surgical patients with 50%-69% stenosis in the NASCET study, there was only moderate benefit to reduce stroke risk, as the rate of ipsilateral stroke was 15.7% in those surgically treated compared with 22.2% in the medical group.12
B. Benefits Both carotid endarterectomy and carotid artery stenting have been shown to be beneficial in the setting of significant stenosis of the extracranial carotid artery in the setting of atherosclerotic disease.
C. Trials and Studies
1. SAPPHIRE The first trial, Stenting and Angioplasty with Protection in Patients with High Risk of Endarterectomy (SAPPHIRE) trial showed noninferiority of carotid artery stenting compared with carotid endarterectomy.19
2. CREST Subsequently, the Carotid Revascularization Endarterectomy versus Stenting Trial (CREST) randomly assigned patients with symptomatic or asymptomatic carotid stenosis to undergo either carotid artery stenting or carotid endarterectomy.11
The primary composite endpoint was stroke, myocardial infarction, or death from any cause during the periprocedural period or any ipsilateral stroke within 4 years after randomization.
The results of this trial showed that the risks did not differ significantly between the carotid artery stenting group and the carotid endarterectomy group.
Because of the results of this trial, carotid artery stenting emerged as one of the primary treatments for carotid artery atherosclerotic disease in select patients.
3. ACES The Asymptomatic Carotid Emboli Study (ACES) demonstrated that there was a higher risk of ipsilateral stroke risk with embolic signals on transcranial Doppler (TCD) ultrasound than in those without, suggesting that patients with asymptomatic carotid disease should undergo TCD to evaluate for microemboli.20
4. Endarterectomy for Asymptomatic Carotid Stenosis Study Revascularization for asymptomatic carotid disease was studied in the Endarterectomy for Asymptomatic Carotid Stenosis Study.21,22
This study was a large-scale study, including 1662 patients, and compared carotid endarterectomy with best medical management with best medical management alone. CT angiography was used to identify patients with greater than 60% stenosis of the extracranial carotid artery, using the NASCET Criteria for measurement of carotid stenosis.
Patients were randomly assigned to either surgery plus best medical management or medical management alone.
A composite primary outcome of stroke or death occurring in the perioperative period and ipsilateral cerebral infarction was used.
This study was stopped early, given evidence of a clear benefit in the carotid endarterectomy group.
These data were further supported by the Asymptomatic Carotid Surgery Trial (ACST).23
5. These studies are not thought to be generalizable to modern clinical practice because optimal medical therapy has improved in the current era as compared with the time of these studies (2004-2010).24,25
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