Page 8 - Carotid and peripheral vascular interventions textbook
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                    PATHOPHYSIOLOGY                                 plaque  buildup  and  greater  carotid  intima-media
                                                                    thickness. The global prevalence of carotid disease,
                        The most common pathophysiology of carotid artery   def ned as greater carotid intima-media thickness by
                    stenosis is the progressive narrowing of the carotid artery   1.0 mm or greater in people ages 30-79 years, was estimated
                    caused by development of atherosclerosis plaque, which   to be 27.6%. However, the prevalence of carotid stenosis,
                    is composed of lipid substances, calcium, and thrombus.   def ned as 50% or greater stenosis, was only 1.5%. These
                    These plaques have a tendency to develop at the points of   numbers are consistent with another study that revealed
                    carotid bifurcation and along vessel areas of curvature (10).     the incidence of carotid stenosis in the general population
                    Hemodynamic forces acting at carotid bifurcation     to be about 3% (18). This f nding suggested that routine
                    locations have a function in restricting intimal thickening     screening to detect carotid stenosis should not be
                    in these areas. Both in vitro and in vivo studies have     recommended for general adults.
                    reported that disrupted f ow and low-shear conditions
                    cause endothelial dysfunction and cause stenosis (11,12).  ETIOLOGY

                        The  two  primary  mechanisms  of  stroke  in
                    extracranial  ICA  disease  are  distal  embolization       The  most  common  etiology  of  carotid  artery
                    and  low-f ow  phenomenon  due  to  insuff cient     stenosis  is  atherosclerosis. The  other  causes  are
                    collateral circulation distant from a hemodynamically   f bromuscular dysplasia (FMD), vascular injury, and
                    signif cant occlusion or stenosis (13). A diffuse-weight   carotid dissection or radiation therapy. Patients that have
                    imaging MRI study showed that an acute ischemic     vascular disease at other territories as well as risk factors
                    injury in ICA occlusive disease is mostly multiple (14).    such as hypertension, diabetes mellitus, hyperlipidemia
                    These results reinforce the fact that embolism from     and smoking have greater risk for developing carotid
                    an  atherosclerotic  plaque  rupture  is  the  principal     artery atherosclerosis. The lesion is normally unifocal
                    mechanism of ischemic stroke. In addition, thrombosis     and 90% are identif ed within 2 cm from the ICA origin.
                    and low cerebral blood f ow are other possible mechanisms      FMD  is  a  rare  disease  that  mainly  involves
                    which are caused by gradual plaque growth and luminal     medium-sized arteries. The vessels involved are usually
                    narrowing. Hemodynamic insuff ciency can occur when   at the mid and distal ICA and renal arteries (19). This
                    any conditions that interfere with cerebral perfusions   disease most commonly affects middle-aged females.
                    such as orthostatic, hypotension or volume depletion   The clinical manifestation varies from asymptomatic
                    are added on to the carotid occlusion, particularly if    to TIAs or cerebral infarction, associated with stenosis,
                    the contralateral carotid disease has severe stenosis.     dissections, aneurysms, or complete occlusion.
                    This low f ow mechanism can explain the infarction in      Vascular injury can cause subsequent carotid stenosis.
                    the border zone areas or so called ‘watershed infarction’.  Torsion and transient occlusion have the effect of creating
                                                                    a temporary functional arterial stenosis. Sometimes this
                    EPIDEMIOLOGY                                    vascular injury results in an intimal tear and thrombus

                        The prevalence of atherosclerotic carotid disease      Dissection of the extracranial ICA can happen
                    differs between studies, depending on the def nition     spontaneously or linked with trauma, such as penetrating
                    used, race, population risk factors, and investigative     neck injuries, intraoperative lacerations and percutaneous
                    tool used for diagnosis (15,16). From a recent study     carotid angiography. The etiology of carotid artery
                    using ultrasonography on people aged 30-79 years   dissection results from an intimal tear. That tear may cause
                    (17), there were substantial variations in prevalence     complete or partial occlusion, traumatic pseudoaneurysm,
                    between each region worldwide. The Western Pacif c     cerebral emboli, or dissection. Cystic medial necrosis
                    region experienced the biggest share of global cases,   with deterioration of muscle f bers together with internal
                    followed by the regions of South-East Asia, Europe,     elastic laminae have also been identif ed.
                    the Americas, the Eastern Mediterranean, and Africa.      Radiation therapy is normally used to treat malignant
                    Current smoking habits, hypertension and diabetes    neck tumors and can affect extracranial carotid vessels.
                    were conf rmed as general risk factors for both carotid     Such radiation-induced carotid stenosis has been linked
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