Carotid stenosis is a narrowing of the carotid artery due to the buildup of plaque. The bifurcation of the common carotid artery is the most frequent site for development of extracranial cervicocephalic atherosclerosis. The most serious consequence of carotid stenosis is a stroke, which has the potential to occur when blood flow to the brain is restricted. The brain's supply of blood may be restricted due to pasts of the plaque breaking off (in pieces called emboli) to cause a physical blockage or due to the decreased diameter of the artery minimizing the amount of blood flowing to the brain. Significant narrowing occurs when the diameter of the vessel is decreased by 70 percent to 60 percent.
Population-based studies reveal that the prevalence of carotid stenosis is .5 percent in the sixth decade and increases to 10 percent in people over the age of 80. Although the vast majority of cases are asymptomatic, carotid occlusive disease is responsible for up to a quarter of the reported strokes in the United States.
Carotid stenosis and even occlusion may remain asymptomatic when the plaque buildup is gradual enough to allow time for collateral circulation. Upon physical examination, a carotid bruit may hint at the presence of asymptomatic cervical internal carotid stenosis. The stenosis can be easily detected with an ultrasound probe placed on the side of the neck near the carotid arteries.
Imaging tests to diagnose carotid stenosis include the following options, selected based on the patient's presenting conditions:
Standard carotid noninvasive studies (CNIS)
- Direct Tests: Assess flow and vascular morphology at the bifurcation of the common carotid artery.
- Duplex ultrasound scanning: B-mode ultrasound image combined with range gated assessment of flow at the bifurcation of the common carotid artery
- Triplex ultrasound scanning: Duplex scanning combined with "real time" two-dimensional flow images superimposed on the B-mode image.
- Indirect Tests: Assess the hemodynamic effect of a stenotic lesion at the bifurcation of the common carotid artery or more distally in the internal carotid artery.
- Transcranial Doppler (TCD): Assess intracranial arterial and ophthalmic artery flow
Magnetic resonance imaging/magnetic resonance angiography (MRI/MRA)
- Time-of-Flight (TOF) uses repetitive radiofrequency pulses to suppress stationery tissues. The unsuppressed protons of flowing blood are then used to create a vascular image.
- Phase Contrast (PC MRA) is a subtraction technique in which moving protons acquire a phase shift proportional to their velocity during the application of a bipolar gradient. The phase contrast sequences provide background tissue suppression and can also provide velocity and directional information.
The prominent interventions for carotid stenoses include carotid endarterectomy or endovascular angioplasty and stenting.
Surgical carotid endarterectomy which entails removing the fatty deposits from one carotid artery, has been a traditional means for revascularization. The efficacy of surgical carotid endarterectomy for treatment of symptomatic carotid stenosis has been examined by numerous randomized, controlled trials.
Endovascular Angioplasty and Stenting
Endovascular angioplasty is performed under local anesthesia, avoiding the major complications of general anesthesia and the local discomfort of an incision in the neck. The technique consists of percutaneous insertion under local anesthesia of a sheath into the femoral artery in the groin. A catheter is then weaved through the femoral artery toward the carotid artery. Angiograms are taken, granting a roadmap of the best passage through the stenosis. An inflatable balloon angioplasty catheter is then inflated in order to achieve satisfactory dilatation. After the dilatation, the balloon catheter is removed proximal to the stenosis. In the case of stent insertion, the spring wire mesh is coiled over a deflated angioplasty balloon and springs open when the balloon is inflated. The stent is then left behind against the wall of the artery to maintain the integrity of the artery.
The risks associated with either treatment of carotid artery stenosis are the potential for embolism, vessel dissection and stroke due to temporary occlusion of the treated artery. The neurosurgeons at The Nebraska Medical Center will address the potential for complications during pre-operative clinic visits.