Paul D. Dimusto
John E. Rectenwald
Gilbert R. Upchurch Jr.
Presentation
A 67-year-old man is referred to your office after a right-sided neck bruit was detected by the patient’s primary care physician on routine physical examination. The patient has a past medical history significant for hypercholesterolemia and hypertension that are managed medically with a statin and a beta blocker. He also takes an aspirin daily. The patient has a 40 pack-year tobacco use history and continues to smoke 1 pack per day of cigarettes. The patient denies any neurologic symptoms, including difficulty with speech, sensory or motor deficits, or amarosis fugax. He denies any history of transient ischemic attack (TIA) or stroke. On physical exam, a right neck bruit is confirmed, and bilateral upper-extremity pulses are equal. There are no deficits on complete neurologic exam.
Differential Diagnosis
The most likely diagnosis in this case is asymptomatic internal carotid artery (ICA) stenosis given the patient’s history of smoking and hypercholesterolemia. Other pathologies that could cause a neck bruit include a carotid aneurysm, dissection, carotid body tumor, or reversal of flow in the vertebral artery secondary to “subclavian steal.” All of these can be detected on duplex ultrasound exam.
Workup
The initial diagnostic imaging test for suspected carotid artery stenosis is duplex ultrasound. This allows for gray-scale evaluation of the degree of stenosis along with Doppler estimation of the blood flow velocities in the area of stenosis. The peak systolic velocity (PSV) in the ICA and the estimate of the percent occlusion caused by the plaque are the primary factors involved in determining the degree stenosis (Table 1). The ratio of the ICA to common carotid artery (CCA) PSV and the ICA end diastolic velocity (EDV) are additional parameters that can be used to classify the stenosis. The degree of stenosis can be estimated as none, <50%, 50% to 69%, 70% to 99%, or total occlusion based on the duplex results. Occasionally, the extent of the lesion will not be able to be appropriately visualized with ultrasound, usually due to a high lesion. In this case, computed-tomography angiogram (CTA) is useful in defining the extent of the lesion and the degree of the stenosis (Figure 1). While the gold standard for measuring the degree of carotid stenosis is angiography, it is rarely used now given the reliable results from noninvasive duplex ultrasound scanning and CTA. Most surgeons will make operative decisions based on ultrasound alone. However, angiography does have a role in carotid stenting.
FIGURE 1 • CT angiogram demonstrating a patient with high-grade right carotid artery stenosis in (A) axial section (arrow) and (B) 3D reformat (arrow).
The patient undergoes a carotid duplex scan (Figure 2) with the following results:
FIGURE 2 • Preoperative duplex scan demonstrating high-grade carotid stenosis with elevated peak systolic velocity and high EDV in right ICA.
RIGHT CAROTID DUPLEX:
Images:
CCA: Evidence of minimal and smooth heterogeneous plaque
BULB: Evidence of irregular calcific plaque with acoustic shadowing
ICA: Evidence of extensive calcific plaque with acoustic shadowing
ECA: Within normal limits.
Doppler:
CCA: Within normal limits
BULB: Within normal limits
ICA: 70% to 99% diameter stenosis
ECA: Within normal limits
Vertebral: Antegrade
IMPRESSION:
The right carotid reveals evidence of 70% to 99% stenosis involving the Bulb/ICA.
TABLE 1. Ultrasound Criteria for Diagnosis of ICA Stenosis
CCA, common carotid artery; ICA, internal carotid artery; PSV, peak systolic velocity; EDV, end diastolic velocity. de Weerd M, et al. Prevalence of asymptomatic carotid artery stenosis in the general population: an individual participant data meta-analysis. Stroke. 2010;41:1294–1297.
LEFT CAROTID DUPLEX:
Images:
CCA: Within normal limits.
BULB: Evidence of minimal heterogeneous plaque
ICA: Evidence of minimal heterogeneous plaque
ECA: Within normal limits.
Doppler:
CCA: Within normal limits
BULB: Within normal limits
ICA: Within normal limits
ECA: Within normal limits
Vertebral: Antegrade
IMPRESSION:
The left carotid study reveals no hemodynamically significant disease.
Diagnosis and Treatment
Based on the carotid duplex results, this patient has a high-grade right ICA stenosis without significant disease on the left side. Given this patient’s history, physical examination, and duplex ultrasound results, the diagnosis in this case is high-grade asymptomatic ICA stenosis. A right carotid endarterectomy (CEA) is recommended given the patient’s relatively young age and the results of randomized controlled trials demonstrating a reduction in stroke risk over medical management alone. Smoking cessation, along with continuation of the patient’s statin, beta blocker, and aspirin are also recommended.
The patient is quoted a risk of 3% for combined ipsilateral stroke and death, and a risk of 10% for cranial nerve injury (usually transient). The patient agrees to proceed with CEA. An EKG is obtained at his clinic visit that is normal. He has a good functional capacity, able to walk up two flights of stairs without becoming short of breath. No further cardiac testing is indicated given his young (<70) age, normal EKG, and good functional capacity.
Discussion
Stroke was the third leading cause of death in the United States in 2007, with 136,000 deaths attributed to stroke and cerebrovascular disease. The prevalence of severe asymptomatic carotid stenosis in the general population is approximately 0.1% in men <50 years old to 3.1% in men ≥80 years old. The prevalence in women ranges from 0% for those <50 to 0.9% for those ≥80. Moderate asymptomatic carotid stenosis is more common, ranging from 0.2% to 7.5% in men, and 0% to 5% in women.
The Asymptomatic Carotid Atherosclerosis Study (ACAS) compared the risk of TIA and stroke between best medical management and CEA in 1,662 patients from 39 sites across the United States and Canada. Patients with a carotid stenosis ≥60% by angiography (correlates to ∼75% stenosis by ultrasound) were randomized to aspirin and risk factor counseling alone or aspirin and risk factor counseling plus CEA. The aggregate risk of ipsilateral TIA, stroke, or death in the perioperative period was 5.1% in the patients undergoing CEA versus 11.0% in patients receiving only medical management, for a 53% aggregate risk reduction for CEA.
The Asymptomatic Carotid Surgery Trial (ACST) was conducted in Europe and randomized 3,120 patients from 1993 to 2003 who had >60% ICA stenosis by ultrasound to medical management or medical management plus CEA. Ultimately the medical management was at the discretion of the treating physician but generally included antiplatelet therapy, antihypertensive treatment, and lipid-lowering therapy in the later years of the study. After 5 years, the stroke risk for CEA was 6.4% (including perioperative events) compared to 11.8% for medical management alone, again demonstrating a benefit for CEA.
These studies have been criticized for a relatively high stroke rate in the CEA group, and because medical management has improved since they were conducted, mostly due to the benefits of statins. Some claim that aggressive modern medical management can reduce the risk of stroke to at least that of the CEA group in the published studies, if not lower. This option of medical management alone may be best for patients who are at high operative risk; however, it has not been fully evaluated in modern randomized trials.
Additionally, carotid artery stenting (CAS) has become a third option for the management of carotid stenosis. However, trials have not shown CAS to be superior to CEA in terms of stroke outcomes, especially in most asymptomatic patients. Carotid stenting can be useful in patients with high-grade lesions with concomitant high-risk anatomic factors that would make open surgery difficult. These anatomic factors include previous CEA with recurrent stenosis, prior ipsilateral neck radiation, previous ablative neck surgery, common carotid stenosis below the clavicle, contralateral vocal cord paralysis, and the presence of a tracheostomy or stoma.
Until further trials can be completed comparing modern medical management including statin therapy, traditional CEA, and CAS, the issue of how to best manage a patient with high-grade asymptomatic carotid stenosis will continue to be debated. The Society for Vascular Surgery issued practice guidelines in 2008 for the management of atherosclerotic carotid artery disease to help guide physicians. They recommend best medical management, including blood pressure control, glucose control for diabetics, lipid reduction, and smoking cessation, for asymptomatic patients with a <60% stenosis. For asymptomatic patients with ≥60% carotid stenosis, CEA with medical management is recommended, as long as the perioperative risk is low. The committee recommended against CAS for patients with asymptomatic stenosis of any grade, with the possible exception of those patients with ≥80% stenosis with high-risk anatomy (defined above).
Surgical Approach
CEA can be performed under local or general anesthesia depending on surgeon’s preference. The GALA trial, published in 2008, was a large randomized trial comparing the incidence of stroke, myocardial infarction, or death within 30 days between patients who had CEA under local anesthesia versus general anesthesia. No significant differences were found between the groups. An advantage of local anesthesia is that the patient’s neurologic status can be monitored during the time of carotid artery clamping and a shunt inserted if needed. If the operation is done under general anesthesia, EEG monitoring or carotid stump pressure can be used to determine the need for shunting. Alternatively, routine use of a shunt can be employed.
The patient undergoes appropriate monitoring including a radial arterial line. A cervical block is placed. After prepping, an incision is made parallel to the anterior sternocleidomastoid muscle. The platysma is divided and the sternocleidomastoid muscle is retracted laterally. The carotid sheath is entered and from this point on in the operation, sharp dissection is utilized to reduce the risk of cranial nerve injury. The facial vein is identified, ligated, and divided. Carotid artery dissection is performed with as little manipulation of the artery as possible. The vagus and the hypoglossal nerves are identified and protected. The CCA and the external carotid artery (ECA) are encircled with vessel loops. The patient is systemically heparinized (100 U/kg) and the ICA is encircled distal to the plaque. After 3 minutes, a test clamp of the ECA and ICA is performed. The patient remains neurologically intact; therefore, the CCA is clamped. An arteriotomy is made in the CCA and extended up the ICA until the top of the plaque is reached. The endarterectomy is begun in the CCA. An eversion endarterectomy of the ECA is performed with good back bleeding. A nicely feathering plaque is removed from the distal ICA. All debris is removed with heparinized saline, and a synthetic patch is sewn in with 6-0 monofilament suture. Prior to completing the patch, the ECA and the ICA are back bled and the CCA is forward bled. The patch is completed. Following patch closure, the clamp on the ECA is released first, followed by the CCA, and finally the ICA. An intraoperative duplex scan shows normal velocities (Figure 3) and no evidence of residual debris or stenosis. The incision is closed in layers, a closed suction drain is placed in the subplatysmal space, and the drapes are removed. The patient is neurologically intact and is transferred to the postanesthesia care unit where he receives an aspirin. The patient is monitored overnight for any neurologic changes or errant blood pressure. The drain is removed the following day prior to discharge (Table 2).
FIGURE 3 • Intraoperative duplex scan demonstrating no residual debris or stenosis in the right ICA.
TABLE 2. Key Technical Steps and Potential Pitfalls to CEA with Patch Angioplasty
Special Intraoperative Considerations
It is critical to identify and protect the cranial nerves encountered during the operation to avoid even temporary paralysis. The vagus and hypoglossal nerves are the most commonly encountered; however, the glossopharyngeal can also be exposed, especially in high distal exposures. Care must be taken to not injure the vagus nerve when applying the carotid clamps.
It is also imperative to see the distal end of the plaque to ensure a smooth, feathered end to the endarterectomy. Occasionally, interrupted sutures will be needed to tack down the intima at the distal endpoint. If preoperative imaging suggests that the lesion is high and that adequate visualization of the distal endpoint may be difficult, subluxation of the mandible can be performed prior to the start of the operation to allow for better exposure. If high disease is unexpectedly encountered intraoperatively, the digastric muscle can be divided, the hypoglossal nerve mobilized, the styloglossus and stylopharyngeus muscles can be divided, and finally the styloid process can be fractured to provide adequate exposure.
Postoperative Management
Patients are typically monitored in a moderate-care setting with arterial line blood pressure monitoring overnight following a CEA as manipulation of the carotid bulb and a change in the flow dynamics can cause variations in blood pressure. Changes in neurologic function should also be monitored as while rare, a patient could have a postoperative stroke related to an embolus from thrombus formation at the operative site. Any new neurologic deficit within 24 hours of CEA should be presumed to be of an embolic origin, and the patient should be promptly taken back to the operating room for exploration and thromboembolectomy. Most patients however are discharged home the following day with aggressive blood pressure, glucose, and lipid control, as well as recommendations for smoking cessation if necessary.
The patient is seen in 2 weeks for an incision check and then in 3 months for a repeat carotid duplex to check for restenosis as well as monitor any contralateral stenosis that may be present. Up to 85% of patients with a moderate contralateral stenosis will progress to severe stenosis and require intervention. Therefore, yearly carotid duplex monitoring is recommended.
TAKE HOME POINTS
· Duplex ultrasound scan is best initial diagnostic test for asymptomatic carotid stenosis.
· Patients with high-grade asymptomatic carotid stenosis (70% to 99% by ultrasound) should undergo CEA along with aggressive medical management to reduce their risk of stroke.
· CEA can be performed under local anesthesia with neurologic monitoring, under general anesthesia with EEG or stump pressure monitoring, or with routine shunt use.
· CAS should be reserved for those patients with a stenosis ≥80% and high-risk anatomy.
SUGGESTED READINGS
Abbott A. Medical (nonsurgical) intervention alone is now best for prevention of stroke associated with asymptomatic severe carotid stenosis—results of a systematic review and analysis. Stroke. 2009;40:e570–e583.
de Weerd M, et al. Prevalence of asymptomatic carotid artery stenosis in the general population: an individual participant data meta-analysis. Stroke. 2010;41:1294–1297.
Grant E, et al. Carotid artery stenosis: gray-scale and Doppler US diagnosis—Society of Radiologists in Ultrasound Consensus Conference. Radiology. 2003;229:340–346.
Halliday A, et al. Prevention of disabling and fatal strokes by successful carotid endarterectomy in patients without recent neurological symptoms: randomised controlled trial. Lancet. 2004;363:1491–1502.
Hobson R, et al. Management of atherosclerotic carotid artery disese: clinical practice guidelines of the Society for Vascular Surgery. J Vasc Surg. 2008;48:480–486.
Lewis S, et al. General anaesthesia versus local anaesthesia for carotid surgery (GALA): a multicentre, randomised controlled trial. Lancet. 2008;372:2132–2142.
Toole J, et al. Edarterectomy for asymptomatic carotid artery stenosis. JAMA. 1995;273(18):1421–1428.