Carotid Artery Stenosis Imaging

Updated: Jul 22, 2016
  • Author: Lennard A Nadalo, MD, FACR; Chief Editor: Kyung J Cho, MD, FACR, FSIR  more...
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Overview

Overview

Stroke (brain attack) represents one of the most serious causes of mortality and morbidity in the United States and throughout the world. Each year, 150,000 patients die as a direct result of a cerebrovascular accident (CVA), while 600,000 patients experience the morbidity of aphasia, blindness, or paralysis. Ischemic strokes are the most common etiology (90%) in the United States. Carotid artery stenosis accounts for approximately 10% of ischemic strokes.

The goals of carotid imaging are early detection, clinical staging, surgical road mapping, and postoperative therapeutic surveillance (see the images below). The detection of a clinically significant carotid stenosis represents an important first step in the prevention of cerebral infarction.{ref1-INVALID REFERENCE}

 

Comparison of Carotid Imaging Methods Comparison of Carotid Imaging Methods

 

The selection of an initial carotid imaging study remains controversial. The use of carotid duplex sonography has been widely recommended as a sceening examination. However, a recent review and meta-analysis published by the U.S. Preventive Services Task Force rejected the usefulness of carotid duplex sonography as a screening test in asymptomatic individuals. Duplex carotid sonography remains useful in the initial evaluation of symptomatic patients who present with nonspecific symtoms that may be related to stenotic or embolic carotid stenosis. [1, 2]

Although duplex imaging helps in the detection of carotid lesions in asymptomatic patients, the cost and risk associated with potentially unnecessary follow-up testing and the risk of unnecessary surgical procedures are arguments againt the wider application of carotid sonography in asymptomatic indivduals. The clincial management of coronary artery disease, peripheral arterial stenosis, and hypertension are likely to delay the development of carotid arterial stenosis. The usefulness of carotid arterial screening has been demonstrated in patients prior to elective surgery. There is good evidence in support of an evaluation for carotid stenosis prior to coronary arterial bypass surgery. [3, 4, 5, 6]

The detection of a carotid bruit is a common physical examination finding that may lead to a referral for carotid duplex ultrasonography. The correlation between a carotid bruit and a hemodynamically related carotid stenosis is reported to be between 10 and 20%. False positive physical findings occur whten a cardiac murmur is transmitted to the neck. Stiff, calcified, or tortuous vessels may generate a bruit in the absence of stenosis.

Preferred examination

A complete medical history should be optained prior to performing carotid imaging. Risk factors, family history, and current neurologic symptoms help select an initial test. Carotid duplex ultrasonography, computed tomographic angiography (CTA), or magnetic resonance angiography (MRA) of the carotid artery may be most appropriate in a specific case (see the images below). [7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18]

Carotid Artery, Stenosis. Duplex carotid sonograph Carotid Artery, Stenosis. Duplex carotid sonography in a patient with sudden onset of aphasia. The peak systolic velocity was greater than 400, which is most likely significant. The images are taken from the common carotid artery.

Carotid duplex sonography (US) is a noninvasive means by which to estimate the degree of cervical carotid stenosis.  US has the advantage of being available  as a portable examination in the intensive care unit (ICU) or the coronary ICU. US can be repeated without concern for potential adverse effects of contrast or radiation. Duplex US can be performed in patients with pacemakers, spinal stimulators or aneurysm clips.

Carotid CT angiography is the a commonly performed imaging study in Stroke Centers. The examination is most often performed immediately after the initial admission CT of the brain. Many of the patients are admitted via the emergency room. The carotid CTA (neck CTA) is most often combined with an intracranial CTA  in order to exclude a proximal thrombosis or embolization withn the anterior cerebral circulation. In selected cases carotid (neck) CTA may be performed to differentiate the cause of a neck bruit.

CT and CT angiography in a patient with a load lef CT and CT angiography in a patient with a load left neck bruit and symptoms of a transient ischemic attack. A, CT scan demonstrates that the left jugular vein (LJV) is superimposed on the left common carotid artery (LCCA). B, After electronic removal of the superficial left jugular vein, a high-grade stenosis of the origin of the left external carotid artery (LECA) is demonstrated clearly. Dense calcifications are seen (red arrows) near the origins of both the left external carotid artery and the carotid bulb. The left internal carotid artery is not significantly stenotic.

One of the potential limitations of CT angiography is calcification within plaques in the carotid arteries. Calcification in the carotid bulb and/or the proximal internal carotid artery may be so dense that identification and measurement of the carotid lumen becomes very difficult using CT angiography.

 

CT angiography is sometimes limited by dense calci CT angiography is sometimes limited by dense calcification in the common carotid artery, in the bulb, and in the proximal internal carotid artery.

Carotid CTA is most commonly performed in combination with intracranial CTA. The ability to correlate intracranial vascular disease with findings in the neck often helps confirm clinical significance. 

Surface-rendered 3-dimensional volume CT angiogram Surface-rendered 3-dimensional volume CT angiogram demonstrates a complete occlusion of the right common carotid artery (CCA).
Axial CT angiograms (A and B) demonstrate bilatera Axial CT angiograms (A and B) demonstrate bilateral occlusions of the right and left common carotid arteries (arrows).
Intracranial CT angiogram in a patient with bilate Intracranial CT angiogram in a patient with bilateral common carotid occlusion shows an absence of flow in the right and left internal carotid arteries (ICAs). ACA = anterior cerebral artery, MCA = middle cerebral artery, PCA = posterior cerebral artery, PCCA = posterior communicating cerebral artery.

Time-of-flight (TOF) Magnetic Resonance Angiography (MRA) is based upon the physics of imaging moving blood.  TOF MRA is useful for patients who cannot tolerate iodinated contrast agents used in CTA. TOF MRA is subject to motion degredation artifacts. Crtical arterial stenosis and near occlusions many be falsely seen as short segment areas of occlusion in noncontrasted TOF MRA.

The principals of cervical and cerebral vascular imaging should be followed when evaluating a patient with neurological symptoms such as the patient (see below) with dizziness made worse with exercise.

Oblique magnetic resonance angiogram of the aortic Oblique magnetic resonance angiogram of the aortic arch and proximal subclavian and common carotid arteries in a patient who presented with dizziness, which was worsened by exercise. Blood pressure readings from each arm were of different in value, with the left arm blood pressure more than 20 mm Hg lower than that on the right side. High-grade stenosis of the proximal left subclavian artery is demonstrated (arrow). 20 cc of Magnevist gadolinium-based MRI contrast was injected intravenously in a large antecubital vein at a rate of 2 cc/sec. The image acquisition was electronically timed to best image arterial blood flow.

Visualizaton of the proximal vessels in the chest and lower neck may explain symptoms that are not related to a cerevical carotid or vertebral stenosis.

Oblique 3-dimensional contrast-enhanced magnetic r Oblique 3-dimensional contrast-enhanced magnetic resonance (MR) angiogram of the aortic arch and brachiocephalic vessels shows high-grade stenosis of the proximal left subclavian artery (white arrow). By using such a model, full depiction of the arch, brachiocephalic vessels, and carotid bulbs is possible. Because of superimposed structures, full rotation of the arterial model is necessary. Note the left common carotid artery (LCCA) behind the left jugular vein. The left subclavian artery (LSCA) is seen well (blue arrow). 20 cc of Magnevist gadolinium-based MRI contrast was injected intravenously in a large antecubital vein at a rate of 2 cc/sec. The image acquisition was electronically timed to best image arterial blood flow.

Contrast enhanced MRA  using a gadolinium MR agent offers improved visualization is areas of high grade stenosis where TOF MRA might falsely indicate a short segment occlusion.

Carotid MR angiogram demonstrates very high-grade Carotid MR angiogram demonstrates very high-grade stenosis (arrow) in the proximal internal carotid artery in a patient with a recent onset of stroke.
Carotid artery stenosis. Axial 3-dimensional maxim Carotid artery stenosis. Axial 3-dimensional maximum intensity magnetic resonance (MR) angiogram in a patient with bilateral carotid artery occlusion. Note the absence of flow in the intracranial internal carotid arteries (yellow arrows). The remaining blood flow to the cerebral hemispheres is the result of collateral branches of the vertebral arteries, including the posterior communicating arteries (white arrows).

Carotid duplex imaging is performed most commonly in patients with moderate risk factors. In the author's practice, duplex ultrasonography is the initial triage examination for patients with an asymptomatic bruit and known asymptomatic carotid vascular disease, and in patients with a complete stroke without prior history of carotid stenosis.

In symptomatic patients and for those with abnormal carotid ultrasonographic findings, another imaging test is performed. MRA or CTA offers full depiction of the cervical common carotid artery (CCA) and internal carotid artery (ICA). In most cases, a complete diagnostic evaluation for cerebral vascular disease can be performed using either MRA or CTA. The immediate availability of CTA in most critical care hospitals on a 24-hour basis makes CTA useful in the care of patients who present after hours in the emergency department.

In the selection of patients for acute treatment for cerebral ischemia, axial CT images should be reviewed using the criteria of less than one-third involvement of the middle cerebral distribution or by using the Alberta Stroke Program Early CT Score (ASPECTS).

The role of cervical-cerebral angiography is evolving as less invasive alternative tests have become available. Cervical and cerebral digital subtraction angiography is primarily used in the performance of intravascular interventional procedures, such as carotid stent placement and endovascular thrombosis extraction.

In the author's practice, clinicians routinely request carotid duplex sonography as  a screening examination. Cervical CTA and intracranial CTA are most commonly performed as a part of an acute stroke evaluation. Cervical CTA is most commonly performed for patients who have contraindications for MRI (eg, pacemaker, aneurysm clip) and for those patients in whom the detail of the carotid stenosis is needed prior to surgery.  Cervical MRA using a time-of-flight technique now represents the most commonly performed follow-up examination for symptomatic patients and for asymptomatic patients with significantly abnormal carotid duplex ultrasound results. Gadolinium-enhanced MRA of the aortic arch and cervical circulation is performed for those patients in whom the time-of-flight study is not adequate. Cerebral angiography is generally reserved for patients who have angiographically based carotid intervention.

Devlin et al reported on acute stroke patients who underwent unenhanced brain CT imaging to exclude pathology that would contraindicate emergent carotid thromboendarterectomy (CEA). The authors concluded, based on their findings, that emergent CEA should be considered in patients presenting with large acute strokes based on favorable CT, CTA, and cerebral CT perfusion (CTP) findings. According to the authors, emergent clot localization and physiologic assessment of brain tissue at risk relative to irreversible cerebral infarction utilizing CT, CTA, and CTP can be determined. [19]

Limitations of techniques

Although carotid duplex imaging offers an excellent noninvasive means of an initial evaluation of the extracranial cerebral vessels, the presence of dense calcifications in the carotid plaque tends to make the study less accurate. The quality of the examination is dependant upon the skill of the sonographer. Because carotid duplex imaging does not help in assessing the intracranial portion of the carotid artery, tandem lesions of the ICA may be missed. In a similar manner, proximal stenosis of the innominate artery and the left carotid artery cannot be evaluated near the origins from the aortic arch.

MRA is contraindicated in patients who have (most) cardiac pacemakers, in patients who have (most) cerebral aneurysm clips, or in those who have undergone certain other medical procedures. In addition, MRA is highly motion sensitive. Many patients require sedation. Because of artifacts related to the TOF MRA image, the degree of stenosis may be overestimated. The use of gadolinium-based contrast agents significantly improves the results of carotid MRA .

CTA requires that iodinated contrast agents be injected at a relatively high flow rate. Patients with renal disease may not tolerate intravenous contrast agents. Motion artifacts remain a problem in the uncooperative patient.

Cerebral angiography also involves the injection of iodinated contrast agents via a catheter that has been placed into the selected artery, usually via a transfemoral route. The overall contrast dose is similar to that required for CTA. The performance of catheter-based cervical-cerebral angiography depends on the skill and experience of the angiographer. Overall major morbidity rates have been reported as 0.1-1%. Injury may occur in the form of iatrogenic stroke, injury to the femoral artery, or bleeding around the catheter introduction site. 

Angiograms do not provide much information concerning the nature of the plaque lesion. Cerebral angiography is the most costly means of carotid stenosis evaluation. If cases are selected carefully, the overall risk of diagnostic angiography, together with the morbidity related to carotid surgery, is less than the risk of stroke for the untreated patient (see the image below).

The U.S. Preventive Services Task Force (USPSTF) has issued a recommendation against screening for carotid stenosis in the general population. [1, 2]

Lateral carotid angiogram in a patient who had a r Lateral carotid angiogram in a patient who had a recent transient ischemic attack. Note the multiple areas of deep ulceration in the proximal internal carotid artery and carotid bulb (arrows). Common carotid angiogram shows normal findings. The examination was performed using a 5 French HN1-shaped catheter. The catheter was positioned in the midcervical portion of the common carotid artery. Contrast was injected at a rate of 7 cc/sec for 2 seconds.

 

Pathophysiology

The process of carotid arterial narrowing represents a long-term chronic disease. In the initial phase, fatty deposits affect the inner lining of the vessel. Symptoms are rare unless there is focal ulceration. The most serious adverse effects are noted when a plaque ulcerates or hemorrhages. Such plaques are known as vulnerable or high risk. Such atherosclerotic plaques have a high risk to cause a stroke. Other vulnerable plaques progress rapidly. The factors that determine the risk of a carotid plaque resulting in a stroke include luminal stenosis, plaque composition, and plaque morphology. Bost US and MRI offer insight into the nature of carotid paques based on the amount of lipid material in the plaque and the presence of ulcerations.

Patient education

For patient education information, see the Stroke Center and Dementia Center, as well as Stroke, Transient Ischemic Attack (Mini-stroke), and Stroke-Related Dementia.

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Radiography

Standard radiographs may demonstrate calcification in the carotid vessels in the neck; however, only large calcified plaques are demonstrated on radiographs. The survery of cervical x-rays by radiologists should include comments concerning the extent of carotid plaque calcification. In general, the information provided by radiographs of the neck or skull is not clinically helpful except to alert the clinical physician that the patient may be at risk for carotid stenosis.

In general, calcification in a plaque indicates chronic carotid vascular disease.

The absence of calcification on radiographs of the neck or lateral aspect of the skull does not exclude significant extracranial carotid disease. Dense calcification can be present in the absence of significant carotid stenosis.

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Computed Tomography

Axial computed tomography angiography (CTA) scanning of the cervical carotid and cerebral arterial circulations provides an accurate means of assessing stenosis and carotid plaque and the effects that stenosis and embolization have on the brain. See the images below. Multislice CT scanners allow for the acquisition of thin (eg, 1-2 mm) axial images within a brief time (a single breath hold). CTA of the aortic arch and cervical carotid arteries has been demonstrated as an effective means of assessment of carotid arterial stenosis. The combination of carotid duplex sonography and CTA of the carotid circulation has been demonstrated to be most cost effective. [20]

Carotid Artery, Stenosis. Axial CT of the brain in Carotid Artery, Stenosis. Axial CT of the brain in a patient with the sudden onset of aphasia. The area of decreased density indicated by the arrows represented an acute infarction in the left middle carotid arterial distribution.
Carotid Artery, Stenosis. Axial image of a carotid Carotid Artery, Stenosis. Axial image of a carotid CTA in a patient with right sided weakness and sudden onset of aphasia. The left ICA (yellow arrow) is occluded.
Axial CT angiograms (A and B) demonstrate bilatera Axial CT angiograms (A and B) demonstrate bilateral occlusions of the right and left common carotid arteries (arrows).
Axial CT image of a patient with a focal stenosis Axial CT image of a patient with a focal stenosis of the internal carotid artery. The cavernous sinus (CS) is distended, with an abscess (arrowheads). Stenosis of the intracavernous internal carotid artery was a response to the abscess in this patient.

Intravenous contrast material must be injected rapidly enough (3-4 mL/s for a total volume of 120-150 mL of 300-320 mg/mL nonionic contrast agent) to achieve a contrast density of at least 150 HU or in the innominate and carotid inflow to continuing distally into the intracranial carotid artery. Imaging begins just before the contrast density peaks in the carotid artery. [8, 21, 22]

Initially, all images should be reviewed in the axial plane. Multiplanar and curved multiplanar reformatted images are often helpful. The intraluminal diameter should be measured by using an electronic workstation with electronic calipers. If the image of the carotid artery is enlarged before measurement, error is reduced. Measurements are made across the lumen through the narrowest portion of the proximal ICA and across the area of the ICA that is above the stenosis and is believed to be normal.

The degree of stenosis is calculated according to criteria developed by the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and is reported as a percentage of stenosis.

Doyle et al performed a study to determine optimal validation of carotid duplex ultrasound velocity criteria (CDUS VC) from CTA-derived measurements with the NASCET method for 50% and 80% stenosis. The authors did a retrospective review of all patients who underwent CDUS and CTA from 2000 to 2009. CTA-derived CDUS VC appeared to be reliable in defining 50% and 80% stenosis in patients with carotid artery stenosis, according to the authors. The authors concluded that CTA should be the gold standard imaging technique for validating CDUS VC. [23]

Carotid ulceration

The carotid arteries may be a source of cerebral emboli via release of the contents of the plaque, via turbulence or clot formation on the ulcerated surface. Carotid ulcers are best demonstrated by using focused US or  the higher resolution of catheter angiography; however, the use of multisection CTA increases the likelihood of carotid ulcer identification. Larger, deeper ulcers are successfully depicted with most CTA techniques (see the image below).

CT and CT angiography in a patient with a load lef CT and CT angiography in a patient with a load left neck bruit and symptoms of a transient ischemic attack. A, CT scan demonstrates that the left jugular vein (LJV) is superimposed on the left common carotid artery (LCCA). B, After electronic removal of the superficial left jugular vein, a high-grade stenosis of the origin of the left external carotid artery (LECA) is demonstrated clearly. Dense calcifications are seen (red arrows) near the origins of both the left external carotid artery and the carotid bulb. The left internal carotid artery is not significantly stenotic.

Carotid plaque

Dense calcifications in the carotid artery limit the accuracy of measurements of the degree of stenosis across the plaque if maximum intensity projection (MIP) or shaded-surface display imaging is used. After first attempting to use axial images to measure the degree of stenosis, curved, multiplanar, reformatted images obtained through the lumen help to show the stenosis.

Certain workstation techniques can be applied that can image reverse the pixels above 300 HU. Image inversion subtracts calcified plaque from the image, which tends to result in a clearer image of the contrast agent–filled carotid lumen. Occasionally, contrast may be seen entering the subintimal area of the plaque. Complex and dissected carotid plaques may be detected in this manner.

Carotid thrombosis

Care must be exercised in cases of carotid thrombosis. Very slow flow rates may be missed if the timing of the intravenous contrast agent bolus or the peak density of the contrast material is less than optimal. It is always necessary to compare 3-dimensional (3D) volume images to axial images (see the images below).

Even in the absence of a high-grade stenosis, caro Even in the absence of a high-grade stenosis, carotid ulceration may result in cerebral infarct. Note the deep ulceration (arrow) demonstrated on this 3-dimensional volume image of the right carotid artery. The large vessel shown to the right is the right jugular vein (RJV). CCA = common carotid artery.
Surface-rendered 3-dimensional volume CT angiogram Surface-rendered 3-dimensional volume CT angiogram demonstrates a complete occlusion of the right common carotid artery (CCA).

The intracranial collateralization pattern helps make the diagnosis of thrombosis and offers important clinical information.

Tumors of the cervical region may surround the CCA or the ICAs. One of the advantages of cross-sectional imaging, such as CTA, is the identification of the tissues that surround the carotid and vertebral arteries.

Degree of confidence

Carotid CTA represents a reliable means of estimating the degree of stenosis in extracranial and intracranial vessels. Limitations in the degree of confidence are related to technical factors. Current multisection CT scanners allow for the acquisition of up to 16 sections for each gantry rotation. Each rotation may require as little as 0.4 seconds. Axial collimation for cervical-cerebral CTA is performed by using a collimation of 0.75 mm with a reconstruction of 1.5 mm for each axial image.

Axial images, multiplanar reformatted images, and 3D volume MIP and volume-model images contribute to the sensitivity and accuracy of multisection CTA. By using available multisection CT scanners, extracranial carotid stenosis can be diagnosed to a degree of accuracy equal to or exceeding that of catheter-based angiography.

CT also offers an excellent means of detecting a tumor that might surround the carotid artery in the neck.

When the carotid artery is imaged by using CTA, artifacts include motion, poor cardiac function, and dense carotid calcification. Even so, overall accuracy for carotid CTA exceeds 95%. Intracranial CTA with a multisection scanner reportedly helps in identifying intracranial carotid stenosis with a sensitivity of greater than 98%, a specificity of 99%, and an accuracy of greater than 98%.

Multisection CT scanners have been introduced that acquire 8 scans with each gantry rotation. As a result, CTA now represents the best overall means of investigating carotid stenosis in a less invasive and more cost-effective manner.

Motion artifacts, however, can reduce the diagnostic efficacy of carotid CTA. Sudden movement, breathing, or swallowing by the patient during scanning may result in a misregistration of the axial images on 3D or multiplanar reformatted images. In such cases, only measurements taken from the axial images should be considered.

Diagnostic problems may also occur if the vessels of the carotid bulb are very dilated and torturous. Superimposed jugular veins and arteries may hide stenosis. A careful review of axial images, together with carefully performed curved, multiplanar, reformatted images through the carotid lumen, demonstrates the stenotic area in most patients.

Devlin et al reported on acute stroke patients who underwent unenhanced brain CT imaging to exclude pathology that would contraindicate emergent carotid thromboendarterectomy (CEA). The authors concluded, based on their findings, that emergent CEA should be considered in patients presenting with large acute strokes based on favorable CT, CTA, and cerebral CT perfusion (CTP) findings. According to the authors, emergent clot localization and physiologic assessment of brain tissue at risk relative to irreversible cerebral infarction utilizing CT, CTA, and CTP can be determined. [19]

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Magnetic Resonance Imaging

MRA usually is performed by using 2 primary methods: time-of-flight and ultrashort, T1-weighted imaging (see the images below).

Carotid MR angiogram demonstrates very high-grade Carotid MR angiogram demonstrates very high-grade stenosis (arrow) in the proximal internal carotid artery in a patient with a recent onset of stroke.
Magnetic resonance (MR) angiograms of the cervical Magnetic resonance (MR) angiograms of the cervical vessels and the circle of Willis show marked narrowing of the internal carotid artery (arrow). Flow is nearly absent in the right intracranial internal carotid artery and in the M1 segment of the right middle cerebral artery.
Carotid artery stenosis. Axial 3-dimensional maxim Carotid artery stenosis. Axial 3-dimensional maximum intensity magnetic resonance (MR) angiogram in a patient with bilateral carotid artery occlusion. Note the absence of flow in the intracranial internal carotid arteries (yellow arrows). The remaining blood flow to the cerebral hemispheres is the result of collateral branches of the vertebral arteries, including the posterior communicating arteries (white arrows).

A 3D time-of-flight image of the carotid artery or a contrast-enhanced, short-TE (echo time), short-TR (recovery time) image is interpreted in much the same manner as CTAs or carotid angiograms of the same area. The stenotic area of the ICA should be evaluated according to the North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria.

Carotid artery stenosis is seen in the images below.

Oblique magnetic resonance angiogram of the aortic Oblique magnetic resonance angiogram of the aortic arch and proximal subclavian and common carotid arteries in a patient who presented with dizziness, which was worsened by exercise. Blood pressure readings from each arm were of different in value, with the left arm blood pressure more than 20 mm Hg lower than that on the right side. High-grade stenosis of the proximal left subclavian artery is demonstrated (arrow). 20 cc of Magnevist gadolinium-based MRI contrast was injected intravenously in a large antecubital vein at a rate of 2 cc/sec. The image acquisition was electronically timed to best image arterial blood flow.
Oblique 3-dimensional contrast-enhanced magnetic r Oblique 3-dimensional contrast-enhanced magnetic resonance (MR) angiogram of the aortic arch and brachiocephalic vessels shows high-grade stenosis of the proximal left subclavian artery (white arrow). By using such a model, full depiction of the arch, brachiocephalic vessels, and carotid bulbs is possible. Because of superimposed structures, full rotation of the arterial model is necessary. Note the left common carotid artery (LCCA) behind the left jugular vein. The left subclavian artery (LSCA) is seen well (blue arrow). 20 cc of Magnevist gadolinium-based MRI contrast was injected intravenously in a large antecubital vein at a rate of 2 cc/sec. The image acquisition was electronically timed to best image arterial blood flow.

Time-of-flight imaging

Time-of-flight imaging is performed without an intravenous contrast agent by using a spoiled gradient-echo sequence. The images are displayed with an MIP protocol in multiple projections.

Because of the effects of turbulence, 3D time-of-flight imaging tends to cause overestimation of high-grade stenosis. In some cases, an area of discontinuity may be generated in the area of the stenosis. This results from turbulent blood flow patterns at the point of a high-grade stenosis and within very stenotic longer stenoses.

TOF MRA Artifacts.
Motion during the examination TOF MRA Artifacts. Motion during the examination may cause misalignment of segments of the MRA resulting in the defect in the left common carotid artery (green arrow) and apparent near occlusion in the left common carotid origin. (blue arrow) Both defects are artifacts due to movement of the patient during the study.

Contrast-enhanced MRA

Contrast-enhanced MRA is performed by using a timed and rapid injection of a gadolinium-based contrast agent, such as gadolinium dimeglumine. [9, 10]

Because the volume of contrast agent is limited to 15-20 mL in most cases, timing of the contrast agent bolus and good venous access are essential. The images are obtained by using a short TR, short TE, and T1-weighted technique (TR/TE/flip angle, 4.9/2.4/35°). The images are displayed in multiple projections by using an MIP technique. [24]

MRA results obtained by using a very short-TR, short-TE, gadolinium-enhanced, timed bolus technique can be interpreted in much the same manner as those of carotid angiography and CTA.

The results of contrast-enhanced MRA are closely correlated with angiographic and operative findings. A gadolinium-based contrast agent has the effect of shortening the T1 qualities of the blood flowing through the stenosis. Residual lumen is displayed with high signal intensity. High-grade stenosis tends to remain an attenuated, but visible, lumen. [25] Results of contrast-enhanced MRA are usually better than those of 3D time-of-flight imaging.

Advances in contrast-enhanced MRA have allowed for improved imaging speed without the need for temporal interpolation. Time-resolved, contrast-enhanced carotid MRA with a sensitivity-encoding (SENSE) reconstruction technique enables visualization of the carotid artery without superimposed venous structures.

The early identification of stroke in the vascular distribution of a related carotid stenosis helps in focusing on an ipsilateral carotid lesion. T1-weighted, diffusion-based imaging effectively depicts focal cerebral ischemia (see the images below), and the finding is often correlated with a proximal carotid stenosis. In other cases, intracranial MRA demonstrates no flow pattern, confirming carotid thrombosis. If the flow rate from the internal carotid artery falls below a critical level, a pattern of cerebral infarcts may form in the watershed zone between the anterior cerebral artery and the middle cerebral artery.

Axial T1-weighted echo-planar diffusion image in a Axial T1-weighted echo-planar diffusion image in a patient with high-grade internal carotid stenosis. Arrows point to multiple, small, subacute cerebral infarcts that have resulted from left internal carotid artery stenosis.

The pattern of infarcts between the anterior cerebral artery (ACA) and the middle cerebral artery (MCA) occurred due to a critical stenosis - near occlusion of the left internal carotid artery. 

Axial T1-weighted diffusion MRI demonstrates 3 sub Axial T1-weighted diffusion MRI demonstrates 3 subacute infarcts (arrows) in the medial parietal aspect of the brain in a patient known to have a very high-grade proximal stenosis of the right internal carotid artery.

The pattern of diffusion-weighted MRI lesions seen in the case above may represent  a pattern of embolii or a watershed infarct pattern in the posterior ACA-MCA region.

While noncontrast MRI can be performed in patients who have limited renal function, gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD) in patients with renal failure. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.

Degree of confidence

Intracranial MRA has a sensitivity of 92-95%, a specificity of 91%, and an overall accuracy of 91% in the detection of intracranial carotid stenosis.

Systematic and random errors affect the results of cerebrovascular MRA. Systematic errors are primarily the result of artifacts and are related to 3D time-of-flight imaging. Areas within the carotid artery that generate turbulence may develop a recirculating pattern of blood flow. In the returning blood flow, the lumen is recorded as artifactually narrowed. Short-segment occlusions may be suggested in patients with very high-grade stenosis (>85% stenosis).

Time-of-flight MRA results should be reported in a manner similar to that for carotid duplex ultrasonography results. Although measurements should be attempted using the NASCET criteria, the significance of the recorded stenosis should be reported with caution.

Certain variations of the CCA may be difficult to interpret by using MRA findings. Narrow bands of intimal thickening may result in a high degree of stenosis; however, the central luminal narrowing is difficult to demonstrate on MRA examination. The proximal ICA may become folded or kinked. Such a kink generates turbulence just beyond the fold. A short-segment pseudo-occlusion may be seen on a time-of-flight study.

The ectatic appearance of fibromuscular hyperplasia may be difficult to resolve by using time-of-flight imaging alone.

Random errors may occur when measurements of the internal lumen are made mechanically. Measuring from enlarged images reduces the relative degree of random error.

The spasm of migraine can simulate carotid dissection on MRA studies performed during an acute migraine event. Assessment of the proximal carotid artery near its origin from the aortic arch requires a good contrast bolus, breath-holding and, in general, good cooperation on the part of the patient.

False-negative carotid MRA results are primarily the result of limitations of resolution. Small surface ulcers may not be resolved on MRA images. At other times, deeper ulcers may contain blood clots, which reduce the apparent size of some ulcers.

Platzek et al compared 3D time-of-flight MR angiography (TOF MRA) with contrast-enhanced MR angiography (CEMRA) for carotid artery stenosis evaluation at 3T. Twenty-three patients with internal carotid artery stenosis detected with ultrasonography were examined on a 3.0T MR system. CEMRA detected stenosis in 24 (52%) of 46 carotid arteries, while TOF detected stenosis in 27 (59%) of 46 carotid arteries. According to the authors, TOF MRA yielded significantly higher results for stenosis grade in comparison to CEMRA (P = 0.014). [11]

Findings

Although time of flight MRA has been used primarily for the assessment of luminal diameters across the carotid arterial inflow T1 FSE imaging when performed at the time of MRA can detect hemorrhage within a carotid plaque. Vertebral and carotid dissections may also be identified as areas of increased T1 brightness within an acute dissection.

MRI of the carotid arteries is also valuable in the detection and characterization of vulnerable plaques. Vulnerable plaques have a complex lipid rich content and may show signs of early hemorrhage. Plaques that progress rapidly are also considered to be vulnerable. Luminal stenosis, plaque composition and morphology can be evaluated using MRI with MRA.

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Ultrasonography

B-mode ultrasonography

The ultrasonographic characteristics of symptomatic and asymptomatic carotid plaques are different. Symptomatic plaques are more likely to be hypoechoic and highly stenotic, while asymptomatic plaques are hyperechoic and moderately stenotic. Evaluation of the surface of the plaque has not been demonstrated to be a satisfactory index of plaque instability.

After carotid endarterectomy, intimal thickness varies in the surgical site. The thickness of the neointima has been correlated with carotid wall stiffness and restenosis after carotid surgery. Comparison of current carotid ultrasonographic velocities to those obtained before carotid endarterectomy is important. In general, the velocity of flow should become reduced with successful surgery. However, velocities may remain elevated after surgery due to scar formation, which results in carotid wall stiffness. Restenosis may occur as a result of surgery or generalized atherosclerotic vascular disease.

Doppler ultrasonography

Doppler ultrasonography is the primary noninvasive test for evaluating carotid stenosis. [26, 27, 28]

Primary examination of the carotid plaque is somewhat subjective, because terms such as soft plaque or irregular surface are often used to describe the primary ultrasonographic images. The degree of stenosis is better measured on the basis of the waveform and spectral analysis of the CCA and its major branches, especially the ICA.

As an example, consider the following case history. A 70-year-old man presented with a suspected stroke. Symptoms included right-sided hemiparesis and dysphasia. Duplex ultrasonographic findings revealed significant stenosis of the proximal left ICA.

The image showed mostly soft, echogenic plaque protruding from the posterior aspect of the bulb and origin of the ICA. A fairly narrow residual lumen remained. Spectral Doppler imaging confirmed the high-grade stenosis, with peak systolic velocity of 325 cm/s and diastolic velocity of 105 cm/s. In the author's laboratory, a diastolic cutoff of 90cm/s is used to distinguish 60-79% from 80-99% lesions in patients such as this man.

The blunted flow in the distal ICA was compatible with the high-grade, proximal obstruction. The CCA showed narrowing of approximately 40%. The opposite ICA was only mildly narrowed and demonstrated normal findings on spectral Doppler examination. The patient underwent carotid angiography. Angiographic findings helped to confirm an 80% ICA stenosis.

The patient was eventually treated with carotid endarterectomy. Follow-up studies in the author's laboratory (not shown) demonstrated a fully patent ICA. Some residual hemiparesis remained on the right side, but the patient was much improved from his status after the initial stroke.

Many published lists exist of carotid flow velocities, which are associated with a graduated degree of stenosis. A listing of flow velocity/carotid stenosis criteria used in the author's department is shown in the table below.

Table. Carotid Stenosis Criteria (Open Table in a new window)

Stenosis Peak Systolic Velocity (cm/s) Peak End Diastolic Velocity (cm/s) Peak Systolic Velocity Ratio
< 50 < 150 < 50 < 2.0
50-59 150-200 50-70 2.0-2.5
60-69 200-250 50-70 2.5-3.0
70-79 250-325 70-90 3.0-3.5
80-89 325-400 70-100 3.5-4.0
90-99 >400 >100 >4.0
Occlusion Not applicable Not applicable Not applicable

Doppler ultrasonographic findings associated with stenosis

Ipsilateral CCA-to-ICA flow ratios may not be valid in the setting of contralateral ICA occlusion.

CCA waveforms may have a high-resistance configuration in ipsilateral ICA lesions, while ICA waveforms may have a high-resistance configuration in ipsilateral, distal ICA lesions. In addition, ICA waveforms may be dampened in ipsilateral CCA lesions.

Long-segment ICA stenosis may not have high end-diastolic velocity.

Velocities supersede imaging in grading stenosis.

Imaging can be used to downgrade stenosis in the setting of turbulence caused by kinking.

In addition to the typical evaluation of the flow rate in the proximal ICA, it has been shown that the flow directly within the ophthalmic artery is highly specific for severe carotid stenosis.

Transcranial Doppler ultrasonography

Transcranial Doppler imaging is sensitive and specific in the detection of hemodynamically significant intracranial ICA stenosis. By using a mean flow velocity of 100 cm/s, transcranial Doppler images help in identifying most intracranial stenotic lesions, with good specificity.

Degree of confidence

The success of duplex ultrasonography (see the images below) depends on careful technique. Results vary somewhat among laboratories. The author's practice has chosen to base its results on a composite mix of the published results comparing the degree of proven stenosis versus flow velocity and ICA-to-CCA velocity ratios. Results should be reported in the context of established criteria as a percentage of stenosis. The table above represents the criteria used in the author's practice. The results should be confirmed with carotid CTA or carotid MRA before surgery.

Carotid Artery, Stenosis. Duplex carotid sonograph Carotid Artery, Stenosis. Duplex carotid sonography in a patient with sudden onset of aphasia. The peak systolic velocity was greater than 400, which is most likely significant. The images are taken from the common carotid artery.
Carotid Artery, Stenosis. Duplex sonographic image Carotid Artery, Stenosis. Duplex sonographic image taken from the common carotid bulb several hours following the sudden onset of aphasia.
Carotid Artery, Stenosis. Proximal duplex sonograp Carotid Artery, Stenosis. Proximal duplex sonography of the left ICA in a patient who presented with the sudden onset of aphasia.
Carotid Artery, Stenosis. Duplex sonography of the Carotid Artery, Stenosis. Duplex sonography of the external carotid artery in a patient who presented with the sudden onset of aphasia.

Discovery of a reversed direction of flow in the ophthalmic artery is closely associated with high-grade ipsilateral ICA stenosis, with a sensitivity of 55%, a specificity of 100%, a negative predictive value of 82%, and a positive predictive value of 100%.

Transcranial duplex ultrasonography with a threshold of 100 cm/s helps in identifying hemodynamically significant lesions, with a sensitivity of 93.9% and a specificity of 91.2%.

The use of duplex ultrasonography is not valid in the setting of contralateral ICA occlusion. CCA waveforms may have a high-resistance configuration with ipsilateral ICA lesions. ICA waveforms may have a high-resistance configuration in ipsilateral distal ICA lesions. ICA waveforms may be dampened with ipsilateral CCA lesions. Long-segment ICA stenosis may not have high end-diastolic velocity. Velocities supersede imaging in grading stenosis. Imaging can be used to downgrade stenosis in the setting of turbulence caused by kinking.

After carotid surgery, recorded flow velocities may be elevated more than those recorded during preoperative examinations. Comparison of the results of the current examination to those of a prior study is essential.

After carotid surgery, recorded flow velocities may be elevated more than those recorded during preoperative examinations. Comparison of the results of the current examination to those of a prior study is essential.

Degree of Confidence

The reports of the results of carotid sonography are not always consistent with clinical purpose of the examination. The use of the term "significant" stenosis is not always consistently used in a manner that is actionable for patient care. The degree of stenosis as estimated by carotid stenosis (except for complete occlusion) should be reported in the appropriate range of stenosis such as 50%-69% rather than as a specific degree of stenosis. [29]

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Nuclear Imaging

Single photon emission CT (SPECT) scanning and positron emission tomography (PET) scanning of the brain may demonstrate areas of cerebral ischemia versus areas of complete cerebral infarction. [30, 31, 32] However, these studies provide only indirect imaging information related to carotid stenosis.

By using a dynamic imaging method, an assessment of the inflow of technetium-99m (99m Tc) hexamethylpropylamine oxime (HMPAO) can be used to estimate the hemispheric cerebral blood flow. If such an assay is combined with a provocative challenge with acetazolamide, it is possible to differentiate patients with migraine from patients with an irreversible cerebral ischemia.

There may, however, be confusion in the findings between an infarct of the brain and a low-grade brain neoplasm or abscess. Moreover, in the evaluation of stroke, false-negative findings may occur in small areas of infarction, which may be below the resolution of a nuclear examination. Comparison with other studies (such as CT scanning or MRI), which have higher resolution, is recommended.

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Angiography

Carotid angiography via a catheter injection of contrast agent has been considered the standard of diagnostic imaging of the cervical and intracranial carotid arteries against which other techniques were judged (see the images below). In recent years, catheter-based cerebral angiography has been performed less often, as other less invasive diagnostic techniques have improved. One of the primary disadvantages of catheter angiography is neurological complications. Neurological complication rates for the performance of catheter cerebral angiography have been reported to be approximately 2.6%, with a 0.14% rate of permanent strokes. [33]

Common carotid angiogram shows normal findings. Th Common carotid angiogram shows normal findings. The examination was performed using a 5F HN1-shaped catheter. The catheter was positioned in the midcervical portion of the common carotid artery. Contrast was injected at a rate of 7 cc/sec for 2 seconds. Note the slightly dilated shape of the distal common carotid artery and the proximal internal carotid artery (carotid bulb). ec = external carotid artery; f = facial artery; l = lingual artery; ic = internal carotid artery; im = internal maxillary artery; o = occipital artery; p cer = posterior cerebral artery; p com = posterior communicating artery
Lateral common carotid angiography demonstrates co Lateral common carotid angiography demonstrates collateral vessels that form after a long-standing complete occlusion of the internal carotid artery.
CT and CT angiography in a patient with a load lef CT and CT angiography in a patient with a load left neck bruit and symptoms of a transient ischemic attack. A, CT scan demonstrates that the left jugular vein (LJV) is superimposed on the left common carotid artery (LCCA). B, After electronic removal of the superficial left jugular vein, a high-grade stenosis of the origin of the left external carotid artery (LECA) is demonstrated clearly. Dense calcifications are seen (red arrows) near the origins of both the left external carotid artery and the carotid bulb. The left internal carotid artery is not significantly stenotic.
Common carotid arteriogram demonstrates dilatation Common carotid arteriogram demonstrates dilatation (black double arrow) of the internal carotid artery beyond the high-grade stenosis (white arrow). This poststenotic dilatation is associated with hemodynamically significant stenosis.
Lateral carotid angiogram shows that the cervical Lateral carotid angiogram shows that the cervical carotid artery (CCA) is narrowed, but it has a smooth outline. The supraclinoid internal carotid artery (ICA) is occluded. Note the enlarged ophthalmic artery (Opthal A.), which functions as a major collateral.
Anteroposterior intracranial carotid angiogram sho Anteroposterior intracranial carotid angiogram shows absence of the normal middle cerebral arterial branches. Image also shows incomplete occlusion of the suprasellar internal carotid artery near the origin of the M1 segment of the right middle cerebral artery.
Angiogram of the carotid artery near the skull bas Angiogram of the carotid artery near the skull base in a patient with a significant fracture of the skull base. Internal carotid artery compression and focal spasm is due to hemorrhage resulting from a pseudoaneurysm (arrow) of the upper cervical internal carotid artery. Treatment of this stenosis requires vascular control of the proximal and distal carotid artery. In this case, the stenosis is primary spasm, which might be considered a protective response to direct carotid artery injury.

The diameters of stenosis can be measured directly, and luminal diameter ratios can be expressed. All contrast-enhanced angiographic studies depend on the radiographic density of iodinated contrast agent compared with normal blood and the density of the wall of the carotid artery (see the images below).

Thoracic arch angiography was performed with a 5F Thoracic arch angiography was performed with a 5F pigtail catheter positioned in the ascending aortic arch. 20 cc of iodinated contrast was injected for 2 seconds. An oblique lateral cervical arteriogram was displayed by using a subtraction technique. Although the contrast agent was injected into the arch, both the carotid stenosis (arrows) and the carotid ulcerations (arrowheads) are demonstrated. ICA = internal carotid artery.
Oblique lateral cervical angiogram obtained by usi Oblique lateral cervical angiogram obtained by using an injection into the aortic arch. Thoracic arch angiography was performed with a 5F pigtail catheter positioned in the ascending aortic arch. 20 cc of iodinated contrast was injected for 2 seconds. Although a very high-grade right internal carotid stenosis is depicted (rc), superimposition of the jugular vein (v) makes its evaluation difficult. Selective common carotid angiography has the advantage of fewer superimposed vessels. lc = left carotid.
Lateral selective right common carotid arteriogram Lateral selective right common carotid arteriogram. Only the proximal few centimeters of the internal carotid artery are patent (arrow). Selective catheterizations in the performance of carotid angiography provide higher resolution (smaller field of view), high concentrations of intraluminal contrast agent, and extended angiographic imaging (longer runs of images). The almost occluded internal carotid artery is evaluated better by using selective common carotid angiography.

Lesions may be smooth, irregular, or focal, or they may involve a long segment (see the image below).

Thoracic arch angiography was performed with a 5F Thoracic arch angiography was performed with a 5F pigtail catheter positioned in the ascending aortic arch. 20 cc of iodinated contrast was injected for 2 seconds. The examination demonstrates one of the common variants of normal aortic arch (AA) development in which both the innominate artery (IA) and the left carotid artery share a common origin. The right common carotid artery (RCA) and the right internal carotid artery are irregular and narrowed. The long, multisegment areas of stenosis are believed to result from the effects of radiation therapy to the right side of the neck in this patient. Effects of radiation therapy are related to adverse effects on the vascular supply to the carotid or vertebral artery in the radiation field.

The NASCET study was based on images created during catheter angiography (see the image below).

North American Symptomatic Carotid Endarterectomy North American Symptomatic Carotid Endarterectomy Trial (NASCET) stenosis measurement. CCA = common carotid artery, D = narrowed diameter, ECA = external carotid artery, ICA = internal carotid artery, and N = normal diameter.

Angiographic technique

In the author's institution, all cervical-cerebral angiography is performed by using the Seldinger technique. The procedure initially involves entering the lumen of the artery of access with an 18-g or 19-g needle. The right femoral artery is used as access in most cases, while the left femoral artery, the left axillary artery, or the left brachial artery may be used for percutaneous catheterization for cerebral digitally subtracted technique (DSA) when the femoral artery cannot be used because of severe aortoiliac artherosclerotic disease.

A heparin-coated guidewire is passed through the hub of the needle into the lumen of the artery. Often, a Safe-T-J-shaped guide wire is used initially to avoid intimal trauma. A 4F or 5F pigtail catheter is generally introduced over a 0.035-inch guide wire into the ascending aortic arch. Nonionic contrast (320 mg/mL of organically bound iodine) is injected at a rate of 20-25 mL/sec for a total volume of 40-50 mL. The left anterior oblique projection is most commonly obtained. If imaging is performed using a DSA, less contrast material is needed.

After the shape, smoothness, and patency of the proximal right CCA, the right subclavian artery, the left CCA, and the left subclavian artery are inspected, a catheter is selected to assist in the selective catheterization of the right CCA, the left CCA, and either vertebral artery or both of them. A 0.035-inch guidewire with a soft, straight tip is used to exchange the pigtail catheter for either a simple angle-tip catheter (eg, one with an HN1 shape) or one with a more complex hook or short-radius, curved shape.

The guidewire chosen for the exchange may have a variable degree of flexibility in the distal several centimeters near the tip. With the guidewire leading into the proximal right and left CCA origins, the cerebral-shaped catheter is positioned in the CCAs below the carotid bulb. Vertebral injections are performed with the catheter in the vertebral artery near the origin of the vertebral artery to avoid spasm.

After a small test injection is made to verify the location and security of the catheter tip position, each of the carotid arterial circulations is studied. Images in a 30° ipsilateral left anterior oblique or right anterior oblique projection are obtained to clearly outline the carotid bifurcations. In some cases, the lateral and the anterior projections are needed.

Digital subtraction angiography (DSA) performed by using a C-arm imager permits an optimal degree of rotation based on the patient's anatomic form. Imaging should include the intracranial carotid circulation in most cases. Selective catheterization of 1 or both vertebral arteries should be performed if clinically indicated in patients with vertebral basilar symptoms.

Each injection of contrast agent into the CCA is given at a rate of 6-7 mL/sec for a total volume of 10-12 mL, depending on the estimated flow rate in the CCA. The larger total volume of contrast and the greater flow rate are reserved for adult patients with a rapid heart rate, such as trauma victims. Selective vertebral artery angiography is generally performed using an injection rate of 4-5 mL/sec, for a total volume of 6-8 mL. In general, the DSA technique requires less contrast agent than older cut film angiographic techniques.

The degree to which intracranial arteries beyond the ICA-MCA trifurcation must be studied should be based on an understanding of the patient's clinical presentation and symptoms. Collateral circulation is best understood by having full visualization of the intracranial circulation, as well as the aortic arch and cervical carotid circulations.

Measurements and other findings

The most common method used to express measurements of the carotid artery is the NASCET criteria, which state that a percentage of stenosis is expressed as a factor of 100, ie, the diameter of the normal ICA located above the carotid bulb divided by the diameter of the proximal ICA at the narrowest point.

Special consideration must be given when there is a critical degree of stenosis, often termed the string sign. The presence of contrast agent in a markedly restricted lumen may be an indication of a critical proximal focal stenosis or longer segmental narrowing. Depiction of residual intracranial arterial flow helps to establish patency (see the image below).

Lateral common carotid angiogram shows appropriate Lateral common carotid angiogram shows appropriate measurements (arrows) for calculating the degree of stenosis by using the North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria.

Other findings noted on carotid angiography include calcification, ulceration (see the first image below), fibromuscular hyperplasia, carotid kinking or folding (see the second and third images below), focal thrombus formation (see the fourth image below), and intimal dissection.

Lateral carotid angiogram in a patient who had a r Lateral carotid angiogram in a patient who had a recent transient ischemic attack. Note the multiple areas of deep ulceration in the proximal internal carotid artery and carotid bulb (arrows). Common carotid angiogram shows normal findings. The examination was performed using a 5 French HN1-shaped catheter. The catheter was positioned in the midcervical portion of the common carotid artery. Contrast was injected at a rate of 7 cc/sec for 2 seconds.
Lateral common carotid arteriogram in a patient wi Lateral common carotid arteriogram in a patient with a neck bruit. Note the focal narrowing of the proximal internal carotid artery (arrow). In severe cases, the kink may require carotid artery reconstruction. Common carotid angiogram shows normal findings. The examination was performed using a 5 French HN1-shaped catheter. The catheter was positioned in the midcervical portion of the common carotid artery. Contrast was injected at a rate of 7 cc/sec for 2 seconds.
Anterior left common carotid arteriogram in a pati Anterior left common carotid arteriogram in a patient who presented with a loud left neck bruit. Note the horizontal line (arrow) in the proximal internal carotid artery, which represents a focal folding of the carotid artery. This configuration has been termed a kink. The bruit results from the turbulent blood flow through the focal narrowing. Common carotid angiogram shows normal findings. The examination was performed using a 5 French HN1-shaped catheter. The catheter was positioned in the midcervical portion of the common carotid artery. Contrast was injected at a rate of 7 cc/sec for 2 seconds.
Lateral common carotid arteriogram in a patient wi Lateral common carotid arteriogram in a patient with transient ischemic attacks. A small filling defect is noted in the common carotid bulb (arrow). A small blood clot was found at surgery, with intimal ulceration at the base of the clot. Common carotid angiogram shows normal findings. The examination was performed using a 5 French HN1-shaped catheter. The catheter was positioned in the midcervical portion of the common carotid artery. Contrast was injected at a rate of 7 cc/sec for 2 seconds.

The plaque may become complicated by marked intimal thickening or subintimal hemorrhage.

After a carotid thrombosis forms, extensive collateralization patterns may be demonstrated, or partial recanalization may occur, resulting in a complex pattern of alternating narrowing and dilatation (see the image below).

Lateral angiogram of the internal carotid artery ( Lateral angiogram of the internal carotid artery (ICA) in a patient with a prior complete occlusion of the internal carotid artery. The irregular lumen (arrows) is consistent with recanalization of the thrombosis. Common carotid angiogram shows normal findings. The examination was performed using a 5 French HN1-shaped catheter. The catheter was positioned in the midcervical portion of the common carotid artery. Contrast was injected at a rate of 7 cc/sec for 2 seconds.

Degree of confidence

Findings on catheter-contrast angiography of the carotid artery are accurate if measurements and calculation of the degree of stenosis are made carefully using an enlarged image. Systematic and random errors may occur during stenosis measurement. The calculation of the degree of stenosis should be based on the NASCET criteria if possible.

False-positive examinations may occur if injection of the contrast agent is not timed properly, resulting in a washed-out appearance on the image.

If subtracted images are developed, overlying metal or dense calcifications result in shadowing of some of the plaque-artery lumen, making an accurate measurement of the residual lumen difficult. Movement, coughing, and the presence of metal artifacts may prevent an accurate examination. Rapid injection may cause a standing wave to form, which may appear similar to fibromuscular hyperplasia.

False-negative results may occur if a nonselective angiographic technique is used. Superimposition of other arterial and venous structures may prevent adequate depiction or measurement of the stenosis.

Despite technical limitations, catheter-based angiographic studies remain the most accurate means of assessing the degree of carotid stenosis.

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Intervention

The appropriate treatment for carotid stenosis depends on the presence of ongoing symptoms such as transient ischemic attack or small infarcts, the grade or severity of the stenosis, and the complexity of carotid plaques. Critical stenosis and complex plaques with suspected hemorrhage are often treated in an urgent or emergent manner. The traditional surgical treatment has been carotid endarterectomy. More recently, endovascular repair by carotid stenting has been applied. In cases of bilateral stenosis, carotid stenting is generally performed within the most symptomatic stenosis first. Simultaneous bilateral carotid stenting has been reported to be feasible with acceptable risks. [33] The overall complicaton rate for carotid artery stenting in high-risk patients has been reported to be approximately 8%. [34]

Precarotid Stent Angiogram.
A moderately high gra Precarotid Stent Angiogram. A moderately high grade stenosis is demonstrated in the proximal internal carotid artery. The patient was symptomatic, with episodes of TIA in the carotid artery distribution.
Post carotid stent placement.
Following the place Post carotid stent placement. Following the placement of a stent (white arrows) in the proximal internal carotid artery, there is a residual stenosis near the distal margin of the carotid plaque. Because of the tortuous course of the distal cervical ICA, the stent failed to advance beyond the distal margin of the carotid plaque. The patient was heparinized during the procedure.
Carotid Stent Placement.
This carotid stent has s Carotid Stent Placement. This carotid stent has successfully expanded the proximal ICA with no significant residual narrowing. The patient was heparinized during the procedure.

 

Duplex sonography is the safest and least costly means by which to screen for cervical carotid stenosis. The risks related to contrast agents, endovascular procedures, and carotid endaterectomy represent a difficult balance between the risk of stroke occurring from the carotid stenosis and the risk of an iatrogenic complication. Medical treatment to prevent or delay the generation of carotid plaque and antiplatelet treatment should be considered first. Intervention should be applied when the imaging studies indicate a critical lesion or in the event of new symptoms.

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